Hiss with AC-DC buck supply: how shielding ?

[mauros]

Hi everybody,

i bought two bucks 220V to 9V like this

eBay auction: #https://www.ebay.com/itm/NEW-High-G...hash=item3aedf56b33:m:mU9l2J_hWAfiMR8zs66GTXw]https://www.ebay.com/itm/NEW-High-G...hash=item3aedf56b33:m:mU9l2J_hWAfiMR8zs66GTXw

to power two sets of pedals effects for my guitar. It works all but I hear from the speaker a hiss that changes the frequency depending on the changes I make to pedal effects. A linear power supply with a transformer I have already realized but it interferes with the inductance of the wah wah pedal and i feel hum. In this video, a mu-metal sheet solves the problem of noise, but it costs too much.




Make some changes low cost to improve shielding ?

Cheers !

[PChi]

The noise may be due to them electrical noise on the output (most likely) or from radiated noise. Before plugging in please watch some of the videos by Bigclivedotcom on YouTube.

[mauros]

Thanks for replying but I did not understand if you want to tell me that in Bigclivedotcom's videos I find the solution or whether it is dangerous what I'm doing.

[PChi]

I can't see the Ebay listing.
Sorry I wasn't clear,  some of the power supplies bought by Bigclivedotcom from Ebay have been dangerous. 2 bucks is suspiciously cheap.
The video appears to show the effect of shielding the magnetic field from I presume a conventional 50 Hz transformer. Steel will also work at screening magnetic fileds (if it is the problem) but not as well as mumetal.

[ogden]

i bought two bucks 220V to 9V like this

Make some changes low cost to improve shielding ?

Simply don't use switching supplies for audio applications Video is not related to hiss problem, it's more or less "snake oil" scam

Indeed you can (try to) make EMI filters for high frequency noise filtering, but easiest fix for you is to get Wall Warts. They do not "hiss" but "hum" instead - because are AC tranformer-based. Linear regulator inside pedal most likely will be able filter low frequency hum w/o problems.

A linear power supply with a transformer I have already realized but it interferes with the inductance of the wah wah pedal and i feel hum.

Just don't put those transformer-based supplies close to pedal!! You need to plan your layout of supplies and audio gear - put them as far away as possible. Then you will not need to build shields. Well, if you really have no way to somehow split gear/supplies - put all the supplies in the solid aluminium box. Box made out of ferrite would be even better.

[mauros]

Linear regulator inside pedal most likely will be able filter low frequency hum w/o problems.

What do you mean ?

Edit:

At the moment I did not think audio switching is noisy, I did the purchase and I realized this

although it would be very convenient especially for the small size

[ogden]

Linear regulator inside pedal most likely will be able filter low frequency hum w/o problems.

What do you mean ?

I mean PSRR of linear regulator. The lower frequency of the noise coming into regulator - the better chances it will be filtered out.

For mains tranformer-based DC supply ripple frequency is 100/120 Hz after rectification. Switching supplies usually operate in 50KHz and up frequencies, with harmonics going into MegaHertz range. This noise is able not only propagate through cables, leak through linear regulator unfiltered, but also radiate all around as radio waves.

https://en.wikipedia.org/wiki/Power_supply_rejection_ratio

At the moment I did not think audio switching is noisy, I did the purchase and I realized this

although it would be very convenient especially for the small size

Those indeed are switching supplies. - Crap which MUST be avoided on stage by all means.

In your place I would test every component one by one in minimal setup: guitar+pedal+amp. If you hear hum when tranformer based DC supply is located >= 1m away from pedal - try to change supply. Maybe it's isolation is faulty. Try swapping pedal as well. Why don't you rent equipment which is known to not hum and by swapping check which part of your setup causes problems?

[mauros]

Guitar, cables, amps and all pedals are ok but one thing I have neglected to say is that the problem is generated by the inductance that is inside the wah wah that captures the magnetic fields in its vicinity, and indeed I hear the hum which changes in intensity with the movement of the power supply.

Edit:
If I set the power supply to 50 cm, the noise disappears, but I would like to fix it under the pedalboard so I would avoid carrying pedalboard + power supply separately, even with the risk of forgetting somewhere 

[ogden]

the problem is generated by the inductance that is inside the wah wah that captures the magnetic fields in its vicinity

Then don't put magnetic fields in it's vicinity or get rid of this wah wah and get another one which does not capture magnetic fields 

If I set the power supply to 50 cm, the noise disappears, but I would like to fix it under the pedalboard so I would avoid carrying pedalboard + power supply separately, even with the risk of forgetting somewhere 

So you want to fix power supply under pedalboard and whats worse - route AC mains there, only because you are afraid to forget it somewhere? I would just buy couple of spare Wall Warts... Maybe instead of consulting electronics forum, you shall consult doctor and address your memory problems?

You can try to use 1/2 inch steel plate as a magnetic shield 

[mauros]

Do you are making a fool of me ?  When you are over 50, memory can betray you but that's not the main problem. I want to optimize by assembling everything you need in the pedal and if possible, I would like to eliminate the hum due to the interference of the magnetic fields

[ogden]

Do you are making a fool of me ?  When you are over 50, memory can betray you but that's not the main problem. I want to optimize by assembling everything you need in the pedal and if possible, I would like to eliminate the hum due to the interference of the magnetic fields

Just kidding, never mind. To sum up your case - personally I would not risk to bring AC mains wires close to sensitive pedal you have. What's worth convenience if quality can suffer in result? Who knows what noise will ride in the AC mains wires of next stage? After all I do not see huge difference between low power Wall Wart with DC cable compared to AC mains cable. Even length of cable is close. One just have bigger plug but thinner cable, that's it. Both does not cost much, both can be lost.

In case you are putting supply into pedalboard - 1/2-inch plate indeed was overstretch You shall test with lighter plates first, see results. Just do tests - what can I say. Also consider wah wah pedal upgrade. NEVER ever use switching supplies to power audio gear.

Good luck!

[mauros]

Regardless of my musical need, let's suppose the problem is just to figure out how to reduce EMIs from a switching power supply like an economical AC-DC buck. My question is, can I use such a filter ?
http://ka7oei.blogspot.it/2014/08/completely-containing-switching-power.html

How should the components be sized ?

[ogden]

Regardless of my musical need, let's suppose the problem is just to figure out how to reduce EMIs from a switching power supply like an economical AC-DC buck. My question is, can I use such a filter ?
http://ka7oei.blogspot.it/2014/08/completely-containing-switching-power.html

Indeed you can use filters. Your supplies needs filters on both - AC side and DC. Also EMI shielding cage will not hurt. It is not feasible to buy crap 2$ supply, then invest your money and time building filters, test results, fix errors and so on. In result it will cost more than proper, clean switching supply with filters already built-in.

How should the components be sized ?

Article you mention provides quite enough information. Anyway you need to learn so you can size components yourself and comprehend what you do. To do it safely you need AC mains isolation transformer. Also oscilloscope will not hurt.

[mauros]

wow, for a beginner I would say that the oscilloscope is the best choice 

cheers !

[ogden]

wow, for a beginner I would say that the oscilloscope is the best choice 

Best choice for beginner - avoid choosing switched mode supply projects. Do you really think that you can pick any area of electronics and just by asking question in the forum - succeed?

[janoc]

wow, for a beginner I would say that the oscilloscope is the best choice 

cheers !

No he did say that "it will not hurt" - i.e. will be useful. That's not quite the same thing. And I agree with that - checking noise levels at the output of the PSU without a scope is difficult, not everything can be heard!

You can have e.g. 100kHz noise from one such switching supply superimposed on the power rail, another such supply for another gizmo will produce 115kHz and these get parasitically mixed together somewhere in an amplifier or the console - producing a nasty 15kHz squeal that will be very hard to debug.  If you are unlucky, the superimposed noise could get amplified and blow out your tweeters as well, depending on the setup.

So don't assume that when the output is silent there is no noise there - you can easily have high frequency noise or even oscillations there that you can't hear. And without a scope you will never know.

I also concur with the idea that buying a $2 supply and then trying to improve it by adding filters and what not is a fool's errand. Even if that $2 supply isn't explicitly a deathtrap (most of these are - that's why the link to BigClive's videos - he is an electrician and shows what to look for when checking such gadgets for basic safety), just the components needed for the filter will cost you at least 10x as much. Plus work, time and the risk that something blows up catching fire or electrocuting someone because you are dealing with mains. Is that worth saving the 30-40 bucks you would pay for a proper and safe wallwart? You could probably even get a free one if you scavenge one from an old laptop, printer or a similar device - they are still switching supplies but likely of much better quality.

Re your pedal - the most logical thing to do would be to shield the coil in the pedal (build a metal can around it) instead of trying to shield everything else around. What if your colleague puts his big guitar combo (or whatever) next to your pedal and you start picking up noise from his power supply/amplifier? If you can't shield it, you can try to replace the inductor(s) with toroidal ones, those are "self-shielding" because the magnetic field is confined inside the core.

[mauros]

Re your pedal - the most logical thing to do would be to shield the coil in the pedal (build a metal can around it) instead of trying to shield everything else around.

The last thing you've written is just what could help me, that is shield the coil inside my pedal. Do you say I have to connect the can of metal to the ground of the pedal ?

[janoc]

Re your pedal - the most logical thing to do would be to shield the coil in the pedal (build a metal can around it) instead of trying to shield everything else around.

The last thing you've written is just what could help me, that is shield the coil inside my pedal. Do you say I have to connect the can of metal to the ground of the pedal ?

Well, that's difficult to say without knowing how your pedal is constructed, but yes, normally you would ground the can to the signal ground of the circuit (not necessarily the metal chassis if there is one).

[floobydust]

mauros, use an old-style adapter with power transformer. I know they are bigger and heavier.

Don't use the SMPS in the photo - no fuse, no safety ground on cheap chinese SMPS that make so much EMI your entire pedal array and audio chain will forever be noisy.
Nobody likes to get electrocuted holding a guitar and grabbing a mic stand.

[vealmike]

Switch mode PSUs can be used with audio, but only with a great deal of care and some expertise.
A ordinary transformer could also be used, but will hum.

By far the simplest solution for powering the Wah-Wah pedal is also the one that will yield the best quality audio for our novice.
[spoiler] [/spoiler]

[IanMacdonald]

I could suggest winding both output wires of the Buck through a  ferrite ring. That often works wonders for induced hiss.

Alternatively if hum is a problem from a linear supply, a small toroidal transformer may be a better option than a rectangular core type.

BTW I would echo the concerns about using any mains PSU from a dodgy manufacturer on music gear.  Stage power is not always reliably earthed, and the combination of sweaty hands on metal strings (or a mike) and a live effect unit case, is a deadly one.  Therefore only use reputable stuff if you want to stay alive. 

[mauros]

I do not think to use that chinese object on stage but the curiosity to understand how to eliminate those noises remains.

[mauros]

I tried an adapter found in a drawer. It works fine but when i activate the wah wah, a pulsating noise comes out of the speaker which in my opinion is always generated by the internal inductance of the wah wah pedal. I tried to surround the inductance with copper tape but the space is narrow and there is a risk of creating a short circuit. The adaptator is this http://truetone.com/1-spot/ , designed exclusively for guitar effects.

[ogden]

I tried an adapter found in a drawer. It works fine but when i activate the wah wah, a pulsating noise comes out of the speaker which in my opinion is always generated by the internal inductance of the wah wah pedal.

Don't you find it strange that any power you throw at your wah wah, results in noise? I would try to swap pedal and upstream audio cables/amp as well. Could be so that power supplies actually are not actual cause of your problems.

[mauros]

Unfortunately it is a problem that afflicts all the guitarists https://tinyurl.com/y9wot8zf and that's why I think the chances are 3, or wah wah away from pedalboard (I prefer not) or the power supply away from wah wah (i prefer not but i could do it) or shield the power supply.

[ogden]

Unfortunately it is a problem that afflicts all the guitarists https://tinyurl.com/y9wot8zf and that's why I think the chances are 3, or wah wah away from pedalboard (I prefer not) or the power supply away from wah wah (i prefer not but i could do it) or shield the power supply.

Wow, lot of hits. Did not know that. - Poor musicians. It is hard to believe that whole music industry is fine with such products that would fail basic EMC immunity tests, would not receive approval at least not as consumer product.

Knowing all this I would drop drop AC power plans, buy 2 or even 3 11V lithium batteries and charger. IMHO such single battery is enough to power all your pedals for 24 hours easily. Just make sure you start with 100% charged battery and have charged spare as well.
 
https://www.rcplanet.com/batteries/battery-packs-surface/traxxas-1400mah-11-1v-3c-25c-lipo-with-auto-battery-id-tra2823x/

If you consider such solution - make sure it's hard case battery. Also would be good to measure consumption of all the pedals so you can size battery (it's mAh) properly.

[janoc]

Wow, lot of hits. Did not know that. - Poor musicians. It is hard to believe that whole music industry is fine with such products that would fail basic EMC immunity tests, would not receive approval at least not as consumer product.

Knowing all this I would drop drop AC power plans, buy 2 or even 3 11V lithium batteries and charger. IMHO such single battery is enough to power all your pedals for 24 hours easily. Just make sure you start with 100% charged battery and have charged spare as well.
 
https://www.rcplanet.com/batteries/battery-packs-surface/traxxas-1400mah-11-1v-3c-25c-lipo-with-auto-battery-id-tra2823x/

You wouldn't believe what sorts of crap is being sold as expensive music/audio gear ...

Unfortunately it is a problem that afflicts all the guitarists https://tinyurl.com/y9wot8zf and that's why I think the chances are 3, or wah wah away from pedalboard (I prefer not) or the power supply away from wah wah (i prefer not but i could do it) or shield the power supply.

On the other hand, "hum" is a very generic term. That could be mains hum (50-60Hz) or it could be high frequency noise. These do not have the same reasons and remedies!

E.g. the low frequency mains hum is most often caused by ground loops because of poor grounding (instruments and the console/amps not on the same ground potential) and rarely by poorly filtered power supplies. If you can't fix your wiring, the way to go is to switch to symmetrical/differential wiring which helps with this - at the cost of some converters. This also helps with common mode noise due to poorly shielded wiring.

The high frequency noise has different sources - poor (switching) power supplies, noisy pre-amps (hiss), amplifiers oscillating, etc. Shielding and differential wiring won't help you here and you need to fix the gear.

Of course, you could always pick up external noise - e.g. because of an unshielded coil or wire acting as an antenna and introducing noise into the system. However, that is a poorly designed/built product and your best bet is to replace it/have it fixed.

So until you know what kind of noise you have and which component is introducing it, you are shooting in the dark and potentially wasting your time and money fixing something that isn't really broken.

[mauros]

So until you know what kind of noise you have and which component is introducing it, you are shooting in the dark and potentially wasting your time and money fixing something that isn't really broken.

The noise i hear with the two AC-DC converters is that of one or more hiss that increase and decrease randomly, but perhaps the idea of ogden to buy lithium batteries is not so bad. Maybe two powerbank ?

Edit:

the absorption of my pedals is less than 700 mA

[janoc]

So until you know what kind of noise you have and which component is introducing it, you are shooting in the dark and potentially wasting your time and money fixing something that isn't really broken.

The noise i hear with the two AC-DC converters is that of one or more hiss that increase and decrease randomly, but perhaps the idea of ogden to buy lithium batteries is not so bad. Maybe two powerbank ?

First try a different supply to make sure the hiss is because of noise on the power rail and not something else - e.g. the pedal picking it up "over the air" from something. Powerbank is not a good idea because they all have switching converters/regulators inside and are not that well filtered (it doesn't matter for their intended use). You are likely to have the same problem if you use one.

Ogden's idea were lithium batteries, not a power bank, i.e. no switching converter anywhere.

Edit:

the absorption of my pedals is less than 700 mA

700mA for a guitar pedal? What the heck is that thing doing? That's one power hungry gizmo ...

J.

[mauros]

Ogden's idea were lithium batteries, not a power bank, i.e. no switching converter anywhere.

I can assure you that there are several power supply switching built for musical instruments, working very well and without noise and i imagine they are well filtered. e.g.
https://www.amazon.com/Truetone-NW1-1-Spot-Adapter/dp/B0002GZLZQ
( I own one, unfortunately in the presence of my wah wah pedal it also generates an annoying pulsating oscillation)

I had bought the two bucks in order to have the GND separated and get the least noise possible. Unfortunately they are coarses and unfiltered

Anyway, i went to buy a power bank 12000 mAh (certainly much less) incredible but it works. No noise no hiss !!!!! Nevertheless I do not trust, I'm afraid that during a concert it can stop working. Maybe it's my paranoia but the power bank I tried is very quiet.

700mA for a guitar pedal? What the heck is that thing doing? That's one power hungry gizmo ...
J.

the pedals are 6 and one only absorbs 500mA  ( http://www.citymusic.com.sg/webshaper/pcm/gallery/lg/p162gr2l2tkg8vbk1omp1shd1d6l2-674-lg.jpg )!

[janoc]

Ogden's idea were lithium batteries, not a power bank, i.e. no switching converter anywhere.

I can assure you that there are several power supply switching built for musical instruments, working very well and without noise and i imagine they are well filtered. e.g.
https://www.amazon.com/Truetone-NW1-1-Spot-Adapter/dp/B0002GZLZQ

I have never said there aren't such supplies or that it can't be done. However, your average Chinese-made power bank is very unlikely to have that level of filtering. If nothing else, you are likely to have high frequency - 200-500kHz - noise from the switching converter "wandering" around. You won't hear that but it could cause issues elsewhere.

( I own one, unfortunately in the presence of my wah wah pedal it also generates an annoying pulsating oscillation)

So that only means it is poorly built as well, regardless of what it says in the marketing spiel or on the sticker. A good supply is not supposed to generate any oscillations!

I had bought the two bucks in order to have the GND separated and get the least noise possible. Unfortunately they are coarses and unfiltered

I do wonder how did you expect to have "GND separated" when your pedal's ground is connected to the rest of the equipment via the signal cable? The power supply doesn't play a role in that - all are galvanically isolated from the mains by a transformer, whether it is a switcher or linear supply (if they weren't, you would have been electrocuted already ...)

Anyway, i went to buy a power bank 12000 mAh (certainly much less) incredible but it works. No noise no hiss !!!!! Nevertheless
I do not trust, I'm afraid that during a concert it can stop working. Maybe it's my paranoia but the power bank I tried is very quiet.

Then why not buying two or even three so that you have a spare, especially when you have found one that works for you? A power supply can also blow up on you on stage, especially cheap junkers like that $2 one you have bought. Having a spare in your kit is always a good idea.

the pedals are 6 and one only absorbs 500mA  ( http://www.citymusic.com.sg/webshaper/pcm/gallery/lg/p162gr2l2tkg8vbk1omp1shd1d6l2-674-lg.jpg )!

Ah ok, that's that fancy digital stuff with LCDs and USB and what not. That would explain it.

I was wondering about the power consumption because an effect "pedal" is rarely much more than a few opamps, pots, some passives and a switch or two. There is no reason why that would normally draw more than about 100mA of current, given that it doesn't do any power amplification.

[mauros]

I have never said there aren't such supplies or that it can't be done.

I was not referring to what you said but i was referring to the noise problem since it is widely believed that power switching is not suitable for audio field because noisy, nevertheless there is some switching product that works

A good supply is not supposed to generate any oscillations!

I agree with you, even if electronics are just a hobby for me, but here the problem is that there is a wah wah that generates a magnetic field with its internal inductance. If I remove the wah wah zero noise. Maybe it's a shielding problem ?

I do wonder how did you expect to have "GND separated" when your pedal's ground is connected to the rest of the equipment via the signal cable?

You're right, but i knew that with the separate gnd outputs the noises are cut down, see below
https://www.guitarworld.com/gear/four-best-pedal-power-supplies-isolated-outputs-noisy

[janoc]

I agree with you, even if electronics are just a hobby for me, but here the problem is that there is a wah wah that generates a magnetic field with its internal inductance. If I remove the wah wah zero noise. Maybe it's a shielding problem ?

Could you record a short video of that showing the problem? It could well be something totally different than a noise pickup by the coil in the wah wah.  Also a few good high res pictures of the innards of your wah wah effect would help, if you dare to open it (could be still under warranty, etc.)

Btw, if that wah wah is the Zoom G3 pedal you have posted a picture of, I would be very surprised by this theory being true - that is a digital device, the only inductors in it would be for a power supply for the CPU/DSP in it. And those are not in the audio signal path at all. The pedal in the video about the mumetal shielding in your original post is an analog one, totally different insides (and could well have some big unshielded inductor in it).

My secret bet is that you are picking up radiated high frequency noise from the junk power supply into a poorly shielded cable or the input pre-amp in the pedal. However, it is difficult to say for sure without seeing the problem first hand.

I do wonder how did you expect to have "GND separated" when your pedal's ground is connected to the rest of the equipment via the signal cable?

You're right, but i knew that with the separate gnd outputs the noises are cut down, see below
https://www.guitarworld.com/gear/four-best-pedal-power-supplies-isolated-outputs-noisy

That is not "separate ground" but separate power supplies (don't have to be in physically different boxes, separate power rails out of one supply are enough) for each pedal. Different issue. Having separate supplies helps because noise from one crappy piece of equipment (which isn't supposed to spew noise on the power rails!) does not interfere with other crappy pieces of equipment (they are supposed to be able to deal with and suppress power rail noise!). In your case it wouldn't have helped because you don't have this problem, IMO. Your noise is apparently from the bad power supply for your pedal, not from other equipment.

BTW, separate ground exists too - if you are using differential signals (so called "balanced wiring") then you don't have to connect grounds. This helps mainly with the 50/60Hz mains hum due to ground loops between different pieces of equipment. Not connecting the grounds together breaks the ground loop and eliminates the hum. Another way of achieving this is by isolating the equipment from each other, either using a transformer or something like a fiber optic cable ("TOSLink").

[mauros]

Could you record a short video of that showing the problem?

With the linear power supply with transformer near the wah wah, the problem and noise are identical to that of the video I posted in the first post where you can see that the guy also has the power supply ( inside a toroidal transformer ) right under his wah wah. Anyway, if tomorrow I can I will make a video using switching power supplies where the type of noise is similar to an annoying thin whistle, although I am more inclined to use the linear one.

Btw, if that wah wah is the Zoom G3 pedal you have posted a picture of, I would be very surprised by this theory being true

no no, the wah wah pedal is a pedal distinct from the Zoom G3 like the video in the first post

My secret bet is that you are picking up radiated high frequency noise from the junk power supply into a poorly shielded cable or the input pre-amp in the pedal. However, it is difficult to say for sure without seeing the problem first hand.

the cables are not shielded but to reduce the ground loops I removed the ground from all the pedals except the first one. The pedals without gnd get it from the jack connectors

That is not "separate ground" but separate power supplies

Sorry, you're right, not separate ground because the ground is in common the same through the jack connectors. This is the power supply I made it myself  https://ibb.co/d984kG

[janoc]

no no, the wah wah pedal is a pedal distinct from the Zoom G3 like the video in the first post

Ah ok.

the cables are not shielded but to reduce the ground loops I removed the ground from all the pedals except the first one. The pedals without gnd get it from the jack connectors

Which are two exactly wrong things to do.  Audio cables carrying small signals (i.e. not speaker cables) always need to be shielded unless they are balanced, full stop. You could very well be picking up all sorts of crap there, even if the signal is at line level and not some weak microphone signal.

Relying only on the ground currents to  flow through the jack connectors (and thus signal cables) will only bring more noise/hum into your system due to the ground potential differences between the devices (ground "moving" in 50Hz rhythm is the same as having 50Hz hum at the input of the device - only the difference matters and it doesn't matter which of the "wires" is "moving"). That's not how you break a ground loop! Now your ground loop is closed through your sensitive pre-amplifier circuit's ground instead.

The way to fix that is to do exactly the opposite - you connect the grounds of all your devices (pedals) together using a thicker piece of wire. That ensures that all devices are at the same potential and if there are any differences for whatever reason, they will equalize through this wire and not through the signal wiring (and thus affect the signal ground of the sensitive pre-amps). You will still have a loop but now no noise currents will flow through it where it matters (i.e. in the sensitive parts). If that doesn't help, you will need the transformers I have mentioned above and actually break the loop by isolating the offending device.

Studios also use something called a star grounding but that is likely not a practical setup on stage, where you have multiple power supplies and what not.

You can read a bit about how to properly deal with grounds here (and also how to track down noise issues):
http://analogrules.com/grounding.html

This is a bit more general but goes a bit more in depth in explaining how ground loops happen and why they cause noise problems:
http://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf

That is not "separate ground" but separate power supplies

Sorry, you're right, not separate ground because the ground is in common the same through the jack connectors. This is the power supply I made it myself  https://ibb.co/d984kG

Do the two voltage regulators have each its own transformer winding? Seems like they do, since I see two diode bridges there. If you care about blocking noise I would also consider adding a low pass LC filter at the outputs (choke + capacitor). That will help with any higher frequency noise and will reduce the mains hum. There are also some good tips here:

 https://www.edn.com/Pdf/ViewPdf?contentItemId=4422750

E.g. that capacitor multiplier essentially completely eliminates mains hum from the output without having to use enormous capacitors.

[mauros]

Do the two voltage regulators have each its own transformer winding? Seems like they do, since I see two diode bridges there. If you care about blocking noise I would also consider adding a low pass LC filter at the outputs (choke + capacitor).

Do you want to say something like that? https://upload.wikimedia.org/wikipedia/commons/9/9e/Common_mode_choke_2A_with_20mH_inductance.jpg

In a drawer I found a double choke from 20 mH x 2. Can it also help with the two switching bucks ?

[janoc]

Do the two voltage regulators have each its own transformer winding? Seems like they do, since I see two diode bridges there. If you care about blocking noise I would also consider adding a low pass LC filter at the outputs (choke + capacitor).

Do you want to say something like that? https://upload.wikimedia.org/wikipedia/commons/9/9e/Common_mode_choke_2A_with_20mH_inductance.jpg

In a drawer I found a double choke from 20 mH x 2. Can it also help with the two switching bucks ?

Didn't do any calculations so no idea whether the 20mH is going to make a difference but give it a shot since you have it already. It can't harm anything. It will certainly block/attenuate conducted noise from getting in or out over the power rails - that's why these are used in the power supply filters. It might help with your switching supplies, but that $2 piece of junk likely spews both radiated and conducted noise all over the place, one choke will not fix it.

My original idea was not a common mode choke but a regular one - a classic LC filter.
There are some ideas here:
https://www.murata.com/~/media/webrenewal/support/library/catalog/products/emc/emifil/c39e.ashx

[mauros]

but give it a shot since you have it already.

Interesting article that you have linked. Anyway, i tried to interpose only the double inductor choke (without capacitor) between the AC main and the two bulk switching but nothing changes, i hear equally the high-frequency whistle which remains of the same intensity. If i want to try with an LC filter, the capacitor must be electrolytic with voltage greater than 230V or can I also use ceramics ?

[janoc]

but give it a shot since you have it already.

Interesting article that you have linked. Anyway, i tried to interpose only the double inductor choke (without capacitor) between the AC main and the two bulk switching but nothing changes, i hear equally the high-frequency whistle which remains of the same intensity. If i want to try with an LC filter, the capacitor must be electrolytic with voltage greater than 230V or can I also use ceramics ?

Aaah duh. You shouldn't put it in between the mains and the switchers, that's not where the whine from them is likely to get into your amplifier/effect. What  is a shorter route/path of the least resistance for the noise? Going to the outlet, through the mains, into your amplifier (which I assume is mains powered) while being attenuated heavily by every power filter on the way? Or through the low voltage wire from your switcher to your effect/amplifier?

You need to put the choke on the low voltage side of the supply in this case, between the supply and the device it is powering.

It may still not do much because it is possible the noise is not getting in by conduction (through the wire) but as radiated noise (through "the air"). Only shielding can fix such situation (or, better, tossing the junk power supply in the bin because it obviously doesn't satisfy any EMC compatibility rules and would not be legal to sell in the US or EU at least).

[mauros]

Aaah duh. You shouldn't put it in between the mains and the switchers
You need to put the choke on the low voltage side of the supply in this case, between the supply and the device it is powering.

I tried to put the chuck inductor on the DC input but nothing happens. While, regarding the linear power supply with the transformer that makes the same noise shown in the video in my first post, I understand from the video itself that it is a matter of shielding, but in a few days I should receive the sheets of mumetal and if I solve keeping the power supply under the pedals in my pedalboard, I would say that for me it's okay in this way and I forget the 2 buck switching.

[janoc]

Aaah duh. You shouldn't put it in between the mains and the switchers
You need to put the choke on the low voltage side of the supply in this case, between the supply and the device it is powering.

I tried to put the chuck inductor on the DC input but nothing happens. While, regarding the linear power supply with the transformer that makes the same noise shown in the video in my first post, I understand from the video itself that it is a matter of shielding, but in a few days I should receive the sheets of mumetal and if I solve keeping the power supply under the pedals in my pedalboard, I would say that for me it's okay in this way and I forget the 2 buck switching.

In that case the noise is probably a radiated and not conducted noise - i.e. something in your pedal is picking up the interference over the air. Even if the choke isn't meant for that service, it would have attenuated the common mode switching noise over the power lead at least somewhat.

[mauros]

In that case the noise is probably a radiated and not conducted noise - i.e. something in your pedal is picking up the interference over the air. Even if the choke isn't meant for that service, it would have attenuated the common mode switching noise over the power lead at least somewhat.

It all started because with the power supply I've always used, this
https://www.thomann.de/pics/bdb/115941/9870465_800.jpg, that has never generated any kind of noise, as soon as I inserted a device that I built by myself and which contains Arduino+USB Host Shield, another kind of noise was generated, a pulsating noise. From there I started my odyssey.

[mauros]

Anyway, now I can fix just holding the power supply transformer away even 30 cm from the pedalboard, although it is more convenient for me to have the power supply wired under the pedalboard. I have to wait and hope to definitively solve with the mumetal.

[janoc]

In that case the noise is probably a radiated and not conducted noise - i.e. something in your pedal is picking up the interference over the air. Even if the choke isn't meant for that service, it would have attenuated the common mode switching noise over the power lead at least somewhat.

It all started because with the power supply I've always used, this
https://www.thomann.de/pics/bdb/115941/9870465_800.jpg, that has never generated any kind of noise, as soon as I inserted a device that I built by myself and which contains Arduino+USB Host Shield, another kind of noise was generated, a pulsating noise. From there I started my odyssey.

But you have never mentioned anything about an Arduino there, have you? Don't you think that it could be actually important?

Arduino and the USB shield generating all sorts of noise is totally to be expected - both are bare boards and don't have much of filtering and shielding. Digital logic is very capable of producing all sorts of whirring, clicking noises when it is running.  If that USB shield is the USB host shield, then it even has a DC-DC (aka switching) voltage regulator on board ...

You will want to have that isolated and away from anything handling low level signals.  If the noise disappears when you unplug it, that is not your power supply being noisy but your Arduino causing the problem.

[mauros]

But you have never mentioned anything about an Arduino there, have you? Don't you think that it could be actually important?

You're right, I had discovered a few months ago but I had forgotten because I spent some time on the high frequency noise of the AC-DC converter and equally on the hum of power supply with transformer (like video my first post), ie observing that with one I did not have the noise of the second, unconsciously I had removed from my mind that the cause was Arduino but that I could solve either with the AC-DC or or with the transformer. I admit, I'm very distracted
Anyway, disconnecting my footcontroller with Arduino everything is silent but unfortunately it is a necessary device and must be together with the other pedals.


Edit:

I add that Arduino and all the device is inside an aluminum enclosure

[janoc]

But you have never mentioned anything about an Arduino there, have you? Don't you think that it could be actually important?

You're right, I had discovered a few months ago but I had forgotten because I spent some time on the high frequency noise of the AC-DC converter and equally on the hum of power supply with transformer (like video my first post), ie observing that with one I did not have the noise of the second, unconsciously I had removed from my mind that the cause was Arduino but that I could solve either with the AC-DC or or with the transformer. I admit, I'm very distracted
Anyway, disconnecting my footcontroller with Arduino everything is silent but unfortunately it is a necessary device and must be together with the other pedals.


Edit:

I add that Arduino and all the device is inside an aluminum enclosure

Well, if the problem is the Arduino/USB combo, then fiddling with replacing power supplies will not help you much. It will only add more problems.

What are you using that Arduino + USB shield for? It is well possible that the problem can be solved differently, in a more "audio friendly" manner. If nothing else, put the Arduino on a separate power supply, in a separate grounded metal box and if you have any audio cables connected to it (or something sitting in the USB shield), put low pass filters there. If it doesn't help, you will likely have to replace it with something else.

My guess is that the Arduino itself is relatively silent but the USB shield is the source of the noise due to its  high speed logic and the switching converter.

[mauros]

What are you using that Arduino + USB shield for?

I realized this

If nothing else, put the Arduino on a separate power supply.

If i use two separate wall adapters power supplies ( both switching !!), one for (Arduino + USB) and the other for pedal effects, it's indeed all silent.

Edit:

but I want to use only one power cable

[mauros]

I want to say that because I don't want too many cables under the foot, i would prefer to leave the pedalboard with a single power cord. It would have been perfect the idea of the two AC-DC converters, both for the clutter that negligible weight, but i am not able to shield the produced noise well. Anyway, if the mumetal work i will use the enclosure with two separate linear power supply fix just below the pedalboard and from here I will go out with a single power cable up to the electric socket.

[janoc]

I want to say that because I don't want too many cables under the foot, i would prefer to leave the pedalboard with a single power cord. It would have been perfect the idea of the two AC-DC converters, both for the clutter that negligible weight, but i am not able to shield the produced noise well. Anyway, if the mumetal work i will use the enclosure with two separate linear power supply fix just below the pedalboard and from here I will go out with a single power cable up to the electric socket.

If the noise is getting there because of  a shared and poorly decoupled power rail, swapping the supplies for linear ones will only add weight, heat and other problems (like the stray mag. field from the transformer requiring extra shielding).

If the system is silent with two switching supplies, then you don't need to swap them for linear ones - they are not the problem! It is kinda like fixing a flat tire by replacing the car engine.

The issue with the single power cable can be solved in two ways:

- You use a single supply but connect the grounds of the circuits only in one place (at the supply) and possibly insert some filters in each power rail (large capacitor + choke) to prevent any digital noise from getting into the pedals. Then you have only a single low voltage wire going into the box.  That would be the preferred solution.

- Or you can transplant your power adaptors inside of your enclosure. Then you have only one mains wire going in. However, that is likely going to be too large unless you remove them from their cases and do some mains wiring. If you want to do that I would strongly recommend asking an electrician to do it for you to make sure it is up to standard - getting electrocuted on stage is not fun! Also shielding could be required.

[mauros]

If the system is silent with two switching supplies, then you don't need to swap them for linear ones - they are not the problem! It is kinda like fixing a flat tire by replacing the car engine.

Evident and this will be my last chance in case the mumetal does not work.

The issue with the single power cable can be solved in two ways:
- You use a single supply but connect the grounds of the circuits only in one place (at the supply) and possibly insert some filters in each power rail (large capacitor + choke) to prevent any digital noise from getting into the pedals. Then you have only a single low voltage wire going into the box.  That would be the preferred solution.

I must say that the idea of adding a filter every time I add a pedal discourages me a lot, but it does not guarantee me to solve the problem.

Anyway, a single power supply would be the solution I prefer in absolute and is what I currently do in this way
http://guitargearfinder.com/wp-content/uploads/2017/03/guitar-pedals-daisy-chain.jpg

and at the moment in the daisy chain above, I have ONLY the first cable with the + and - that connect to the board containing Arduino, while on the other connectors i removed the ground, significantly reducing the noise of ground loop: what remains is very normal.

Trying to put the first connector on an analog pedal and a cable with only the ground on Arduino, the noise becomes infernal 

But, as I wrote, with the power supply above everything would be ok until the wah wah switch turned on, otherwise I have this sound ticking

https://instaud.io/_/1wlF.mp3

[mauros]

Instead, the power supply I use in this video consists of the two AC-DC converters and I show the noise generated as soon as the wah wah is inserted

https://streamable.com/hozsj

[janoc]

The issue with the single power cable can be solved in two ways:
- You use a single supply but connect the grounds of the circuits only in one place (at the supply) and possibly insert some filters in each power rail (large capacitor + choke) to prevent any digital noise from getting into the pedals. Then you have only a single low voltage wire going into the box.  That would be the preferred solution.

I must say that the idea of adding a filter every time I add a pedal discourages me a lot, but it does not guarantee me to solve the problem.

No no, you add the filter to the power rail going to the pedals (they share the same power, no?), not for each pedal! It wouldn't hurt but it would be an overkill. We assume the pedals don't introduce noise, the digital stuff does. So basically you split the power into the "dirty" digital part and "clean" analog/pedal part by putting the filter in.

Anyway, a single power supply would be the solution I prefer in absolute and is what I currently do in this way
http://guitargearfinder.com/wp-content/uploads/2017/03/guitar-pedals-daisy-chain.jpg

and at the moment in the daisy chain above, I have ONLY the first cable with the + and - that connect to the board containing Arduino, while on the other connectors i removed the ground, significantly reducing the noise of ground loop: what remains is very normal.

Trying to put the first connector on an analog pedal and a cable with only the ground on Arduino, the noise becomes infernal 

That's because you have the grounding done incorrectly. You should not rely on the ground to be connected by the signal wires only! The best way to wire something like this would be to have the power & ground connected to every pedal & Arduino, but the power grounds meet at a single point only (a "star" system). I.e. not daisy chaining - that causes problems because any voltage drop due to the increased current draw of some of the devices on the chain will be seen right away by the other things on the chain, propagating noise.

Then the signal wires should have ground lifted (the shielding on the signal wires will be grounded only on one side) and your console/amplifier cable should get its reference ground from the above common grounding point instead.  That would very much eliminate issues with ground loops between your pedals/Arduino.

If nothing else, the ground in your daisy chain setup should be a thick piece of wire (or even a copper bar), so that you have a nice low impedance path back to the power supply and the voltage drops between the devices are kept to a manageable level. It is not as good as a proper star ground but it gets close.

Here is a good explanation of this:
http://www.lh-electric.net/tutorials/gnd_loop.html


If would actually help if you could draw a diagram how is everything wired together because I am starting to suspect we may not be talking about the same thing.

But, as I wrote, with the power supply above everything would be ok until the wah wah switch turned on, otherwise I have this sound ticking

https://instaud.io/_/1wlF.mp3

Hmm, that's a weird noise. That's doesn't sound like a switching power supply problem (that would be likely a continuous whine). That tap-tap-tap noise seems to be either something oscillating in the wah wah or your Arduino periodically doing something (e.g. trying to enumerate/communicate with the USB shield) and the pedal is picking up that noise through a poorly decoupled power rail. Does it do that even if you remove the USB shield? Try to pull it off and see whether the noise is gone. If yes, then the Arduino likely needs a better power rail decoupling (assuming the rest of the wiring is done correctly, see above).

[janoc]

Instead, the power supply I use in this video consists of the two AC-DC converters and I show the noise generated as soon as the wah wah is inserted

https://streamable.com/hozsj

Yikes - that is a nasty power supply noise, indeed. But given what you have there -  the converter has no shielding, not much (if any) filtering (likely only a single capacitor at the output!), it is not surprising. I am not sure I would dare to run those cheapo modules as a mains supply - that's asking for getting electrocuted (or a fire), IMO!

Get a proper (i.e. UL certified) mains supply for that, especially if it is meant to be used on stage where you can potentially get water in it, liquids spilled, etc. That will likely solve both the safety and the noise issues - the supplies must be certified for EMC compatibility otherwise they cannot be sold, the cheap junk from China sold on eBay isn't or has fake CE markings. This is not where you want to be penny pinching and good quality power brick will cost you maybe 20-50 bucks tops anyway.

You can even get power bricks that have two different output voltages (e.g. 9V and 5V), if you need that. That will save you the cabling. Alternatively you can get one with a higher voltage to supply e.g. your pedals and then have a low voltage regulator (either linear or switching) to reduce the voltage for e.g. your Arduino (or whatever else you need to power).

[mauros]

Now i have the certitude that i will not use chinese bucks because i do not trust myself, so in alternative i would have:

1) https://ibb.co/d984kG
2) https://www.amazon.com/Truetone-NW1-1-Spot-Adapter/dp/B0002GZLZQ

The first, if i want to keep it together with the pedals, is fine if i put the mumetal under the wahwah as in the video of my first post or, without mumetal, if i keep it away from the pedals.
The second is sensitive to the TAC TAC TAC of Arduino and if with the mumetal also disappears the TAC TAC, then i prefer it to the first because at least it is certified since the first is a do-it-yourself. How do you suggest me to do?

[mauros]

If would actually help if you could draw a diagram how is everything wired together because I am starting to suspect we may not be talking about the same thing.

https://www.photobox.co.uk/my/photo/full?photo_id=500345703815

This diagram refers to the second power supply (1Spot). The ground only on the first pedal and the other the ground comes from the signal cables.

[janoc]

Now i have the certitude that i will not use chinese bucks because i do not trust myself, so in alternative i would have:

1) https://ibb.co/d984kG
2) https://www.amazon.com/Truetone-NW1-1-Spot-Adapter/dp/B0002GZLZQ

The first, if i want to keep it together with the pedals, is fine if i put the mumetal under the wahwah as in the video of my first post or, without mumetal, if i keep it away from the pedals.
The second is sensitive to the TAC TAC TAC of Arduino and if with the mumetal also disappears the TAC TAC, then i prefer it to the first because at least it is certified since the first is a do-it-yourself. How do you suggest me to do?

I don't know your voltage and current requirements for the entire setup, but I was more thinking in terms of something like this:

https://uk.rs-online.com/web/c/power-supplies-transformers/power-supplies-psus/desktop-power-supply/?applied-dimensions=4292047706,4293173688,4293175092,4293174793,4293175046,4293174860,4293175078,4293175088,4294510413

There are also dual supplies, but those have usually 5 and 12V outputs, not 9V. But if that Truetone adapter works, why not. On the other hand, they don't list any FCC/UL certifications, nor any specs whatsoever on their website, so their adapter could well be a cheap supply from Shenzen with a Truetone sticker on it ...

That shape of the case is extremely common in low cost crappy power supplies from there, e.g. this one:


 I think the Truetone one is better than the junker in BigClive's video but the lack of published specs and certifications is a big red flag to me.

The mumetal shielding will certainly not fix that tap-tap noise - that is most likely being carried by the wiring, not radiated (which is the only thing that a metal sheet can fix). The video where the guy has used the mumetal sheet was fixing a mains hum from a 50/60Hz transformer under his pedal, not a digital noise.

What I  suggest to do would be the following:

- Fix your wiring first - i.e. proper star grounding, a single grounding point for all devices on your pedal board. If you don't do this, you are going to be chasing your own tail forever because e.g. 3 devices will work together and connecting the 4th one will introduce hum or noise due to ground loops and noisy ground. It is very likely that once you do this, a lot of noise issues you have with the Arduino and your wah wah pedal will just disappear.

- If the Arduino is still causing trouble, put it on a separate power rail - that could be simply a separate pair of wires to the power connector with a choke and a few capacitors next to the Arduino, to make sure that any noise doesn't propagate from it to the pedals. Also make sure the Arduino is away from any sensitive analog circuitry of the pedals.

- If you still can't solve the above and you want to use the linear supply with a transformer, try to find a toroidal one (like this: https://uk.rs-online.com/web/p/toroidal-transformers/6718956/  or, even better an encapsulated one like this: https://uk.rs-online.com/web/p/toroidal-transformers/2239418/ ). Toroidal transformers will produce much less hum compared to what you have there because the toroid concentrates the magnetic field inside of the ring, very little gets out. An especially good option is an encapsulated one which is magnetically shielded already. That will save you messing with any mumetal sheets (risk of short circuits and what not) and is easier to mount as well - one needs to be careful when mounting a toroid to not create a shorted turn by the mounting hardware.

[janoc]

If would actually help if you could draw a diagram how is everything wired together because I am starting to suspect we may not be talking about the same thing.

https://www.photobox.co.uk/my/photo/full?photo_id=500345703815

This diagram refers to the second power supply (1Spot). The ground only on the first pedal and the other the ground comes from the signal cables.

That link doesn't display - it redirects me straight to the Photobox front page.

[mauros]

That link doesn't display - it redirects me straight to the Photobox front page.

Very strange, if I click on it works for me. Try this

[mauros]

I don't know your voltage and current requirements for the entire setup
.....
But if that Truetone adapter works, why not. On the other hand, they don't list any FCC/UL certifications, nor any specs whatsoever on their website, so their adapter could well be a cheap supply from Shenzen with a Truetone sticker on it ...

I need just under 600 mAh and Truetone provides up to 1700 mA

The mumetal shielding will certainly not fix that tap-tap noise - that is most likely being carried by the wiring, not radiated (which is the only thing that a metal sheet can fix). The video where the guy has used the mumetal sheet was fixing a mains hum from a 50/60Hz transformer under his pedal, not a digital noise.

but I would use it for the same reason as the video adopting the power supply https://ibb.co/d984kG, although I imagine it will not work with digital noise. I would put the mumetal sheet under the wahwah, in what sense do you speak of a shortcircuit ?

- If the Arduino is still causing trouble, put it on a separate power rail - that could be simply a separate pair of wires to the power connector with a choke and a few capacitors next to the Arduino

I powered Arduino separately in two ways:

a) using the linear power supply above with two isolated output
b) using this other type of power supply https://www.solidrop.net/photo-8/hot-sell-caline-cp-05-guitar-effect-pedals-power-supply-ten-isolated-outputs-9v- 12v-18v-voltage-protection.jpg which has outputs in parallel but filtered individually

But only in the first case I tried to put a CLC filter on the input of the power supply without succeeding. Perhaps the values of inductance and capacitors should be better studied 

- If you still can't solve the above and you want to use the linear supply with a transformer, try to find a toroidal one

Initially I did not think about the toroidal, otherwise I would have opted for that, but for now I do not want to spend any more money, and if I do not resolve in any way use this https://ibb.co/d984kG and keep it away from the pedals.

[ez24]

2) https://www.amazon.com/Truetone-NW1-1-Spot-Adapter/dp/B0002GZLZQ

There is also this (from same page as above)

https://www.amazon.com/dp/B012VQ5A7S/ref=sspa_dk_detail_1?psc=1

[janoc]

That link doesn't display - it redirects me straight to the Photobox front page.

Very strange, if I click on it works for me. Try this

I think it works for you because you are still logged in into that page (so a cookie is set). It likely won't work for anyone else unless they create an account or something.

The Imgur picture loads ok:



Now, lets see whether I understand what  you have done correctly:

• You have a guitar pickup connected to something called "over" (I guess some sort of an effect - sorry, I am not a musician!) using a shielded cable (most likely not a coax ...). That then goes into the Zoom effect box and the wah wah effect and out to the amp. OK.
• The Zoom box is powered & controlled by the Arduino using the USB shield. OK.
• The power wiring is, umm ... interesting. So you have decided to distribute only the +9V and the return path is over the shields of all that signal wiring, through the USB shield & the Arduino back to the power supply? And you are wondering why are you having weird noises in the signal?

Guess what happens when the Arduino or the Zoom produce a larger power spike (e.g. because something internally just turned on). More current flows into the ground wire - the ground "jumps" up for a moment (the current doesn't flow back to the power supply instantaneously because of parasitic inductances and capacitances of the wiring).  Because your wah wah, your over  and even the amp get signal ground level from this unstable ground, they see it as a spike in the signal (remember - voltage is a potential difference between two points, it doesn't matter if it is the "red" or the "black" wire changing!) and will happily amplify it - and you suddenly hear stuff like your "tap tap" noise. 

I believe you are doing MIDI control of the Zoom G3 with the Arduino and MIDI happens to have an Active Sense message sent every 300ms to detect whether the device didn't get unplugged. Guess what is the period of those tap-tap noises in the MP3 file you have linked before. Yup, every ~300ms ...

If you have used the star grounding system, each device would have its own power and ground wire back to the supply. Then the above cannot happen because even if the Arduino makes a current spike, that spike will affect only its own ground wire. The rest will still keep their "clean" ground connected to the power supply. The supply has a very low impedance output, so any spikes that get to it will get "eaten" by the large output capacitors and won't propagate to the other devices.

You definitely do need to rewire this - not only because of the noise problems but also because it could literally fry something. The signal circuits aren't designed to carry the power currents of everything you have there. E.g. the USB shield is rated only for 500mA of current - and you are using it to return the current consumed by everything in your setup to the power supply.

but I would use it for the same reason as the video adopting the power supply https://ibb.co/d984kG, although I imagine it will not work with digital noise. I would put the mumetal sheet under the wahwah, in what sense do you speak of a shortcircuit ?

I was thinking about you trying to put the metal foil inside of the power supply case. Sure, if you put it under the wah wah pedal, it will be unlikely to cause a short.

I powered Arduino separately in two ways:

The problem with your Arduino is not the power supply but your bad wiring setup. See above. Once you fix that, the problem will most likely go away.

Initially I did not think about the toroidal, otherwise I would have opted for that, but for now I do not want to spend any more money, and if I do not resolve in any way use this https://ibb.co/d984kG and keep it away from the pedals.

That toroidal trafo costs ~20 bucks. How much did you spend on that mumetal sheet? If you are building something that should last you for a while, you want something that is robust and reliable so that you won't have to do a rubber chicken voo-doo dance around it to get it to behave every time.

However, I would still rather replace the supply with something that is hermetically sealed and professionally made, whether that TrueTone adapter of yours or another one. That homebuilt supply of yours is a problem waiting to happen. The linear voltage regulators will get hot in the plastic box, no components are mechanically fixed to anything ("flapping in the breeze" - imagine what happens after tossing this in your travel case few times - the PCB tracks will break/peel off), there is no fuse, the vent holes will allow dirt & water ingress - I don't know what kind of music you play but I have seen both gear getting rained on and gear getting beer (or worse!) spilled on at events. Do you want to risk that with a mains device?

If some drunkard gets fried because they have spilled beer in your kit and someone finds this gizmo of yours there, you could be in a nasty legal mess even though it was his fault and your power supply was not the source of the injury. In many countries you have no right to do anything with mains unless you are a licensed electrician.

[mauros]

So you have decided to distribute only the +9V and the return path is over the shields of all that signal wiring
through the USB shield & the Arduino back to the power supply? And you are wondering why are you having weird noises in the signal? If you have used the star grounding system, each device would have its own power and ground wire back to the supply.
You definitely do need to rewire this...

Would you tell me how to make the star connection ? I do not know if it can help but in every pedal the ground of the signal is connected to the ground of power.

However, I would still rather replace the supply with something that is hermetically sealed and professionally made, whether that TrueTone adapter of yours or another one. That homebuilt supply of yours is a problem waiting to happen. The linear voltage regulators will get hot in the plastic box...

Some time ago I had kept the home-made linear power supply switched on for more than 2 hours to check the temperatures with a thermometer on the two 7809 regulators and it did not exceed 45 ° C, if this is the problem.
On the fact that I reduced the enclosure to a sieve, I agree, but at most I would keep it behind my back and away from the stage just to avoid water and beer, otherwise I can always buy a new, more sealed enclosure...On the fact that I have reduced it to a sieve, I agree, but at most I would keep it behind my back and away from the stage just to avoid water and beer, otherwise I can always buy a new, more sealed enclosure. I absolutely do not want to risk with the mains power supply 

If some drunkard gets fried because they have spilled beer in your kit ...

You're right, in fact, I had also thought about this, until nothing happens everything is ok, otherwise they are bitter cocks     

[ez24]

Just thinking outside the box

Since mains voltage seems to be a concern, how about using a good used bench power supply, like HP or Power Designs.  You could even use current limit to save things.  OP said he did not want to use a separate supply because he is afraid he would forget it.  So you could come up with a way to attach a lock box to the PS and put your keys inside it so you could not get anywhere.  Just don't be last man out the door.

[mauros]

...using a good used bench power supply, like HP or Power Designs.

They would be too heavy and bulky.

OP said he did not want to use a separate supply because he is afraid he would forget it. 

Of course yes. I use it for jams, record in the studio and at home and of course to go play live and I can not risk not being able to use the pedalboard just because I forgot to put in a suitcase a power supply or a cable.  It is more practical to open the suitcase and connect a plug to the power strip that pull a lot of things out of the suitcase and assemble them at the moment. It seems easy but when you find yourself doing it you always have so many logistical difficulties. Anyway, it's like that
Anyway, usually for practicality the pedalboards are wired with everything on board

https://tinyurl.com/ycw4cs3c

[mauros]

If you have used the star grounding system, as not the source of the injury. In many countries you have no right to do anything with mains unless you are a licensed electrician.

To have a single point of reference for the ground, i could try to put in the mammut the grounds  instead of the positive, that is to reverse the connections. What do you think about it ?

[mauros]

I believe you are doing MIDI control of the Zoom G3 with the Arduino and MIDI happens to have an Active Sense message sent every 300ms to detect whether the device didn't get unplugged. Guess what is the period of those tap-tap noises in the MP3 file you have linked before. Yup, every ~300ms ...

Let me understand, would Arduino send a periodic impulse that has a period of 300 ms? But with the software I can not inhibit it in sending this impulse? Change some libraries ?

[janoc]

If you have used the star grounding system, as not the source of the injury. In many countries you have no right to do anything with mains unless you are a licensed electrician.

To have a single point of reference for the ground, i could try to put in the mammut the grounds  instead of the positive, that is to reverse the connections. What do you think about it ?

I am not quite sure what are you referring to as "mammut". Is that a slang for some sort of a terminal strip? However, if you just reverse the polarity, that will not help you that much - the noise will be still there and now you will also certainly overload the USB shield because it will need to power everything. And that is rated 500mA max. So it will likely die.


The way I would wire your setup:

- Put a DC barrel jack for the power input (you likely have that already).
- Put a decent sized terminal strip there, connect it to your positive pole of the power supply. This is where everything will be getting power from. Don't daisy-chain - that would have the same problems like your current setup.
- Put there a large screw on a chassis where you connect the negative pole of your power supply. This will be your ground.
- Now each device that needs power will have two wires. One that goes to the positive power strip and the other one to your grounding point. It should look somewhat like this (see why is it called a "star" ground?):



- For the signal cables between the devices - use a shielded cable and connect the shielding to ground only on one side. This is important - usually people solder the shielding braid on both sides but then the shielding carries return current too and you get ground loops. We don't want that - we want the return current to go through the common grounding point instead. If anything needs a separate signal ground (i.e. the common power ground isn't enough for some reason), you will run a wire to the star grounding point you have made above. That will avoid any ground loops between the devices.

- The output to the amplifier needs to have both signal and ground connected because it needs to get the reference level - run a ground wire from the connector to your common grounding point again.

Also have a look at the links I have posted earlier, they explain quite well the basic rules of how this works.

Let me understand, would Arduino send a periodic impulse that has a period of 300 ms? But with the software I can not inhibit it in sending this impulse? Change some libraries ?

It could well be your Zoom sending it - it is the side that transmits that sends these when there is nothing else happening on the wire. It is part of the MIDI standard. You could disable it (it is an optional part of MIDI) but that wouldn't help you any - it is a MIDI message as any other, so once you start sending other MIDI messages (Controller, Note on/off, whatever), you will "hear" those as well. You need to fix the wiring, then this will go away.

Some time ago I had kept the home-made linear power supply switched on for more than 2 hours to check the temperatures with a thermometer on the two 7809 regulators and it did not exceed 45 ° C, if this is the problem.

45C is okay, but the rest about your supply still applies. That's not a supply that will withstand the rigors of portable use.

[mauros]

...I am not quite sure what are you referring to as "mammut". Is that a slang for some sort of a terminal strip?
...For the signal cables between the devices - use a shielded cable and connect the shielding to ground only on one side.
...The way I would wire your setup:...
- The output to the amplifier needs to have both signal and ground connected because it needs to get the reference level - run a ground wire from the connector to your common grounding point again.

yes, mammut is properly a terminal strip.
From what you write, if I understand correctly, I deduce that I can use two terminal strips, one for the positive reference and the other for the negative reference. But if the chassis on which the pedals are fixed is made of aluminum, like this https://cdn.marcmart.com/ebay/EC916/3.jpg, could not i drill a hole and make all the ground converge here ? Or do you say that there is some impropriety and better to use two terminal strips, one for the positive reference and one for the negative one ?

45C is okay, but the rest about your supply still applies. That's not a supply that will withstand the rigors of portable use.

Why do you say this ? what problems could I go to?


Edit:

Today the postman gave me the sheets of mumetal and placing them under the wah wah the hum of 50 Hz or 100 Hz disappears. I remember that the hum is generated when I use the power supply with the transformer putting it under the pedalboard together with the pedals. Now I have to try the power supply of Truetone with the star connection of the grounds.

[janoc]

yes, mammut is properly a terminal strip.
From what you write, if I understand correctly, I deduce that I can use two terminal strips, one for the positive reference and the other for the negative reference. But if the chassis on which the pedals are fixed is made of aluminum, like this https://cdn.marcmart.com/ebay/EC916/3.jpg, could not i drill a hole and make all the ground converge here ? Or do you say that there is some impropriety and better to use two terminal strips, one for the positive reference and one for the negative one ?

You don't have to drill a hole into chassis. It would be better if the chassis was grounded but it doesn't matter all that much in this case. Just make sure the chassis is insulated from the pedals in such case in order to not create another ground path, circumventing your star ground.

Of course, if the pedals are screwed down onto the chassis it would be probably better to install the ground there to avoid problems.
You can still use two terminal strips, one affixed directly to the chassis for the ground and one for the 9V.

45C is okay, but the rest about your supply still applies. That's not a supply that will withstand the rigors of portable use.

Why do you say this ? what problems could I go to?

See my comments about the lack of any mechanical support for the components - they are held in place just by soldering. If you drop the supply or toss it in you baggage, the solder joints and the tracks will be stressed - the component leads and the large size work like a lever. After a while they will crack and the components will not have good contact anymore. E.g. if the ground pin of the voltage regulators gets loose you will have a full input voltage at the output - likely quite a bit more than the 9V the gear is meant to work with, frying it. I have seen components even detaching from the board completely and causing a short circuit - quite a problem in a box where you have mains voltage.

Then there is the issue of the mains wiring (lack of fuse), the possibility of water/liquid ingress due to the holes you have made, etc.

Today the postman gave me the sheets of mumetal and placing them under the wah wah the hum of 50 Hz or 100 Hz disappears. I remember that the hum is generated when I use the power supply with the transformer putting it under the pedalboard together with the pedals. Now I have to try the power supply of Truetone with the star connection of the grounds.

Yes, don't leave it like that, happy that the transformer hum is gone. The current wiring will certainly cause you problems in the future.

[mauros]

You don't have to drill a hole into chassis....Just make sure the chassis is insulated from the pedals...

The pedals are held with Velcro, then insulated from aluminum

You can still use two terminal strips, one affixed directly to the chassis for the ground and one for the 9V.

ok

See my comments about the lack of any mechanical support for the components...

I do not know what you mean by mechanical support but the pcb is fixed on two wooden slats through 3 screws

Then there is the issue of the mains wiring (lack of fuse), the possibility of water/liquid ingress due to the holes you have made, etc.

I drilled the holes because I did not find an enclosure of adequate size with provision for ventilation, even if I would not use for more than 3 hours at most and the temperature does not exceed 50 ° C

Yes, don't leave it like that, happy that the transformer hum is gone. The current wiring will certainly cause you problems in the future.

By chance do you refer to the wiring without the star connection of the grounds ? In this case, if the star connection solves the problem, it means that I will use Truetone's power supply


Edit:

I had also foreseen the fuse but I removed it momentarily during the design of the PCB to recover some space to modify the circuit but I forgot to put it back

[janoc]

I do not know what you mean by mechanical support but the pcb is fixed on two wooden slats through 3 screws

What I mean is that the large components need to be mechanically secured to the PCB/box as well, not only soldered. Soldering is insufficient. That's why the voltage regulators have a hole for a screw, for example - so that you can screw them down to a heatsink that is hopefully fixed to the case/board. The large capacitors need to be glued down or strapped to the case. The mains wire must have a proper strain relief to prevent it being torn out of the box. Etc.

I drilled the holes because I did not find an enclosure of adequate size with provision for ventilation, even if I would not use for more than 3 hours at most and the temperature does not exceed 50 ° C

Yes, of course. However, the holes are a serious hazard if you are going to use this somewhere where liquids could get to it - such as when playing at some event.

By chance do you refer to the wiring without the star connection of the grounds ? In this case, if the star connection solves the problem, it means that I will use Truetone's power supply

I mean the wiring you had in the hand-drawn diagram with the only ground connection through the Arduino and the USB shield.

[mauros]

What I mean is that the large components need to be mechanically secured to the PCB/box as well, not only soldered...

Ah ok, the regulators are fixed with a screw to the respective heatsink but often I have seen the heatsink anchored only to the pcb, like mine. To fix the big capacitors, actually some hot glue can put it. About the main wire, not finding a strain relief in my drawers, I opted for a tripolar panel plug like this https://tinyurl.com/y8wrdave but if everything works I'm going to get a smaller enclosure with ventilation and to add a strain relief.

I mean the wiring you had in the hand-drawn diagram with the only ground connection through the Arduino and the USB shield.

Anyway, in a few days I will dedicate myself to "the star", and I hope to resolve definitively 

[janoc]

What I mean is that the large components need to be mechanically secured to the PCB/box as well, not only soldered...

Ah ok, the regulators are fixed with a screw to the respective heatsink but often I have seen the heatsink anchored only to the pcb, like mine. To fix the big capacitors, actually some hot glue can put it. About the main wire, not finding a strain relief in my drawers, I opted for a tripolar panel plug like this https://tinyurl.com/y8wrdave but if everything works I'm going to get a smaller enclosure with ventilation and to add a strain relief.

If the heatsinks are soldered/screwed to the board it is ok. They looked a bit loose to me, especially the bottom one which seems a bit non-standard and without the mechanical support pins.

I wouldn't use hot glue there - the hot glue softens with heat, so it will not do you much good - the parts will come loose over time. It is better than nothing but if you can find Silastic it would be much better. Here is a discussion about it, including some product names:
https://www.eevblog.com/forum/beginners/questions-about-silastic/

I would also probably prefer a fixed power cable with a proper strain relief grommet and even some sealing against moisture. A regular IEC plug is not optimal as it isn't really waterproof in any sense. Also your setup isn't earthed so a three pin plug may not be "cosher" there, depending on the regulations in force in your country. But that question I will leave to an actual electrician to answer, I am not one.

I mean the wiring you had in the hand-drawn diagram with the only ground connection through the Arduino and the USB shield.

Anyway, in a few days I will dedicate myself to "the star", and I hope to resolve definitively 

Good! Let us know how it went.

[mauros]

For the signal cables between the devices - use a shielded cable and connect the shielding to ground only on one side.

Inside each pedal effect the shielding of the signal is connected to the ground of the power supply, so to realize what you say I have to open the pedal and disconnect all these shielding from the ground of the power supply, leaving it connected only on the first or last pedal. Do you confirm this ?

[janoc]

For the signal cables between the devices - use a shielded cable and connect the shielding to ground only on one side.

Inside each pedal effect the shielding of the signal is connected to the ground of the power supply, so to realize what you say I have to open the pedal and disconnect all these shielding from the ground of the power supply, leaving it connected only on the first or last pedal. Do you confirm this ?

You can simply make a cable where the shielding is soldered to the connector only one side, you know 
Probably easier than messing with your pedals.

What you need is that any wire going between two devices  has the shield connected only on one side (doesn't matter which one).

[mauros]

You can simply make a cable where the shielding is soldered to the connector only one side, you know 
Probably easier than messing with your pedals.
What you need is that any wire going between two devices  has the shield connected only on one side (doesn't matter which one).

I did the test only with the two critical pedals, ie the Zoom / Arduino + Wah Wah + a single cable, with shielding connected only on one side, to connect the Zoom output to the input of wah wah but unfortunately the TAP TAP did not go away and it was added even the noise of an airliner parked during taxiing

https://youtu.be/zWUQr6lTicM?t=108

[janoc]

You can simply make a cable where the shielding is soldered to the connector only one side, you know 
Probably easier than messing with your pedals.
What you need is that any wire going between two devices  has the shield connected only on one side (doesn't matter which one).

I did the test only with the two critical pedals, ie the Zoom / Arduino + Wah Wah + a single cable, with shielding connected only on one side, to connect the Zoom output to the input of wah wah but unfortunately the TAP TAP did not go away and it was added even the noise of an airliner parked during taxiing

https://youtu.be/zWUQr6lTicM?t=108

How did you connect the power? Did you use the star grounding? If you only remove the ground and don't fix the rest, it will not work! In fact, it will be worse because now the ground return path for the signal is even worse than before.

[mauros]

How did you connect the power? Did you use the star grounding?

I used two terminal strips, on one I set the positive of the power and on the other the negative of the power. In the first I then connected the positive of the two pedals and on the other terminal I connected the two negatives.

If you only remove the ground and don't fix the rest, it will not work!

"fix the rest"... what do you mean?

Edit:

I mean that I seem to have done as you said or I missed something ?

[janoc]

How did you connect the power? Did you use the star grounding?

I used two terminal strips, on one I set the positive of the power and on the other the negative of the power. In the first I then connected the positive of the two pedals and on the other terminal I connected the two negatives.

If you only remove the ground and don't fix the rest, it will not work!

"fix the rest"... what do you mean?

Edit:

I mean that I seem to have done as you said or I missed something ?

By "rest" I meant implementing the star grounding.

How is the arduino connected? Also by its own pair of wires to the two terminal strips? It would help if you could draw a diagram again how did you connect everything together.

Now for debugging it - if you remove the Arduino and leave only the pedals setup like this - is it still noisy? (power the Zoom from 9V directly, not through USB).

[mauros]

Now for debugging it - if you remove the Arduino and leave only the pedals setup like this - is it still noisy? (power the Zoom from 9V directly, not through USB).

I do not remember if I wrote it but I think it has already said in some of my message that without Arduino I have no kind of noise, connecting it directly to 9V ( NO USB ) and even in daisy chain. It is its presence in the pedal board the cause of all the strange noises, from the ticking with the PSU switching to the humming at 50 Hz with linear power supply with transformer.

[janoc]

Now for debugging it - if you remove the Arduino and leave only the pedals setup like this - is it still noisy? (power the Zoom from 9V directly, not through USB).

I do not remember if I wrote it but I think it has already said in some of my message that without Arduino I have no kind of noise, connecting it directly to 9V ( NO USB ) and even in daisy chain. It is its presence in the pedal board the cause of all the strange noises, from the ticking with the PSU switching to the humming at 50 Hz with linear power supply with transformer.

That's a bit of a red herring.

In your original setup (with the bad ground system), the Arduino has been in the ground return path of *every single signal* on that pedal board. So no wonder you had problems. Any noise it generated or picked up got added to your signals.

I suggest the following to make sure we are able to get rid of the tap tap noise first (that one is added by the digital MIDI signal).

Connect only the Arduino and your Zoom. Remove any other pedals from the signal chain - you can leave them powered, just remove any signal wires. (don't forget to connect the shielding of the cable to your amplifier and from your guitar to the ground of the Zoom/pedal board!)

Is it noisy like this? Do you hear the tapping noise or any other unusual noise? Is the noise still there if you short the input of the Zoom to ground?

If it is still noisy (tapping noise), then the problem is definitely with the Arduino/USB shield noise getting into the Zoom and the Zoom not having it properly filtered internally. That could be a really difficult issue to solve without modifying the device. In such case try to power the Zoom from a separate power supply (not just over USB). If it doesn't help even like that, then we are pretty much screwed.

If it isn't noisy like this, unplug power, take your multimeter and measure resistance between the ground of the input plug and the negative power supply wire. It should be very low (ideally dead short). If it isn't, then the Zoom has separate grounds for the digital and analog parts and you may need to add a grounding connection between the input connector and the star grounding point.

Once you have things working and noise free, continue connecting the other hardware one by one. If the setup suddenly gets noisy, you will know why and can investigate right away.

[mauros]

If it isn't noisy like this, unplug power, take your multimeter and measure resistance between the ground of the input plug and the negative power supply wire. It should be very low (ideally dead short).

Between the negative of the Power Supply and the input ground i measure about 17 Ohms .

If it isn't, then the Zoom has separate grounds for the digital and analog parts and you may need to add a grounding connection between the input connector and the star grounding point. 

Signal input connector ?

[janoc]

If it isn't noisy like this, unplug power, take your multimeter and measure resistance between the ground of the input plug and the negative power supply wire. It should be very low (ideally dead short).

Between the negative of the Power Supply and the input ground i measure about 17 Ohms .

Yikes. OK that's not good but not totally unexpected neither (separated signal and digital grounds are common to reduce noise). In that case connect one grounding wire between the input ground of the Zoom and your star grounding point. That should solve that particular issue.

If it isn't, then the Zoom has separate grounds for the digital and analog parts and you may need to add a grounding connection between the input connector and the star grounding point. 

Signal input connector ?

Your Zoom is a guitar effect processor, no? So it has one (or more) jack where the guitar signal comes in and one (or more) jack where the processed signal comes out, doesn't it? That's what I mean by "input connector". In order to eliminate hums and other noises you have to have a low impedance path to ground for the signal. Since you have measured 17 ohms between the input jack and the power connector, we can't rely just on the path through the power supply (17 ohms is not really "low impedance" by any measure).  That's why the added grounding wire is needed.

If you don't want to mess with the wires, try first to connect the signal cables with the shielding connected on both sides (the usual way). That will add that signal ground where needed. It is not ideal (you could get ground loops and hum) but at least if the power wiring is fixed (i.e. separate power/ground wire pair for each device), it is less likely to cause issues than before. Only if this doesn't work then some more drastic measures will be needed.

[mauros]

...connect one grounding wire between the input ground of the Zoom and your star grounding point. That should solve that particular issue.

I understood what you say, to reset the ddp between the two points but connecting the ground of the Zoom input with star ground ( 23 Ohm) i hear a bump from the amp speaker and the Zoom goes off. I immediately terminated the connection for fear of some failure.

[janoc]

...connect one grounding wire between the input ground of the Zoom and your star grounding point. That should solve that particular issue.

I understood what you say, to reset the ddp between the two points but connecting the ground of the Zoom input with star ground ( 23 Ohm) i hear a bump from the amp speaker and the Zoom goes off. I immediately terminated the connection for fear of some failure.

 Oops. Take your multimeter and measure whether the Zoom doesn't have a voltage between the input signal ground and power ground. That sounds like you have managed to make a short circuit somewhere.

And what is the "ddp"? I don't know that term.

[mauros]

Oops. Take your multimeter and measure whether the Zoom doesn't have a voltage between the input signal ground and power ground. That sounds like you have managed to make a short circuit somewhere.

And what is the "ddp"? I don't know that term.

Ops, I wrote the acronym in Italian --> ddp = voltage (difference of potential)

Anyway, i tried to put two separate power supplies and while I remembered that it did not make noise, instead the noise exists, no tapping but high frequency noise, but only when the wahwah is pressed down (all sounds sharp). At this point, the only solution without noise is a pair of power bank or my dual power supply in which the hum would eliminate it with the mumetal (but uncomfortable).
In my opinion, as you said, i should find a drastic solution. What do you mean by drastic?

[mauros]

Since next week I have to play live, today i tried all the possible power supply combinations that i own and for now i found this quite silent solution: the Truetone for the 4 analog pedals, including the wah wah, and the stock power supply for Zoom G3, placing both in a power strip under the pedalboard, as in this photo http://www.johnhendow.com/wp-content/uploads/2012/04/underside-2.jpg

[mauros]

Given the cable Truetone is quite long and fat I tried to replace it with another Zoom AD16E
https://tinyurl.com/yafgllf5
but I noticed that a noise is generated that I never heard, like the roar of a lion I removed one of the two Zoom AD16E and the I connected it to the wall socket and at that point the lion ran away, instead I would rather keep both in the same power strip

[janoc]

Oops. Take your multimeter and measure whether the Zoom doesn't have a voltage between the input signal ground and power ground. That sounds like you have managed to make a short circuit somewhere.

And what is the "ddp"? I don't know that term.

Ops, I wrote the acronym in Italian --> ddp = voltage (difference of potential)

Ah OK. That sounds like the Zoom is a rather particular gadget, with separate grounds and what not.

Anyway, i tried to put two separate power supplies and while I remembered that it did not make noise, instead the noise exists, no tapping but high frequency noise, but only when the wahwah is pressed down (all sounds sharp). At this point, the only solution without noise is a pair of power bank or my dual power supply in which the hum would eliminate it with the mumetal (but uncomfortable).

Hmm, that seems that the pedals are picking up switching noise from the switching power supply. That supply needs more output filtering, then.

Two power supplies will certainly eliminate the tap-tap because now the Arduino is not sharing the power rails with anything else, so any noise cannot propagate further.

In my opinion, as you said, i should find a drastic solution. What do you mean by drastic?

Well, drastic as in modifying some of the hardware or inserting transformers and such but you seem to have found a combination that works for you in the meantime.

Since next week I have to play live, today i tried all the possible power supply combinations that i own and for now i found this quite silent solution: the Truetone for the 4 analog pedals, including the wah wah, and the stock power supply for Zoom G3, placing both in a power strip under the pedalboard, as in this photo http://www.johnhendow.com/wp-content/uploads/2012/04/underside-2.jpg

Why not? If it works, good enough! 

Given the cable Truetone is quite long and fat I tried to replace it with another Zoom AD16E
https://tinyurl.com/yafgllf5
but I noticed that a noise is generated that I never heard, like the roar of a lion I removed one of the two Zoom AD16E and the I connected it to the wall socket and at that point the lion ran away, instead I would rather keep both in the same power strip

LOL! That sounds like a missing signal ground connection somewhere. Or a feedback. The fact that it goes away when the supplies are not on the same power strip points to the missing ground - in such case the signal will "find its way" elsewhere (such as through the supplies on the same power strip), with all sorts of nasty consequences. Check that all your pedals and the Zoom have actually a common ground connection - if you are using 2 power supplies, the grounds need to be connected together at the star grounding point.

[mauros]

For now I leave everything as it is and I will try this assembly when I go to play for two/three hours continued. Instead I would like to solve another problem for which I will open a new thread. I own two Zoom, one is the one I use with the problems of hiss and noise already treated in this thread and the other Zoom identical to the first one where I have to replace the LCD display that the parent company does not release as spare and I have to arrange myself but I would like to understand how to find what is right for me