Hiss with AC-DC buck supply: how shielding ?

[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