Author Topic: Hiss with AC-DC buck supply: how shielding ?  (Read 6575 times)

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Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #50 on: December 10, 2017, 03:25:45 am »
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
 

Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #51 on: December 11, 2017, 01:49:28 am »

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  :palm:


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).

« Last Edit: December 11, 2017, 01:59:44 am by janoc »
 

Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #52 on: December 11, 2017, 02:07:30 am »
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).
« Last Edit: December 11, 2017, 02:18:07 am by janoc »
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #53 on: December 11, 2017, 03:21:24 am »
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?
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #54 on: December 11, 2017, 05:19:35 am »
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.

« Last Edit: December 11, 2017, 05:21:36 am by mauros »
 

Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #55 on: December 11, 2017, 06:21:20 am »
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.

« Last Edit: December 11, 2017, 06:26:56 am by janoc »
 

Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #56 on: December 11, 2017, 06:23:44 am »
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.
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #57 on: December 11, 2017, 08:17:29 am »
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

 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #58 on: December 11, 2017, 09:07:59 am »
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.
 

Offline ez24

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Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #60 on: December 11, 2017, 10:24:32 am »
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.

« Last Edit: December 11, 2017, 11:03:58 am by janoc »
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #61 on: December 11, 2017, 11:59:27 am »
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     ;D
 

Offline ez24

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #62 on: December 11, 2017, 01:19:48 pm »
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.
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Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #63 on: December 12, 2017, 01:14:46 am »
...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
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #64 on: December 12, 2017, 01:20:20 am »

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 ?
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #65 on: December 12, 2017, 06:30:02 am »

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 ?
 

Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #66 on: December 12, 2017, 08:24:18 am »

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.
« Last Edit: December 12, 2017, 08:28:12 am by janoc »
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #67 on: December 13, 2017, 01:55:05 am »
...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.
« Last Edit: December 13, 2017, 02:38:12 am by mauros »
 

Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #68 on: December 13, 2017, 04:21:19 am »
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.
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #69 on: December 13, 2017, 05:05:27 am »
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
« Last Edit: December 13, 2017, 05:11:35 am by mauros »
 

Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #70 on: December 13, 2017, 07:23:22 am »
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.

« Last Edit: December 13, 2017, 07:29:28 am by janoc »
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #71 on: December 13, 2017, 08:35:05 am »
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  :-+
 

Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #72 on: December 14, 2017, 01:49:26 am »
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.
 

Offline mauros

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #73 on: December 14, 2017, 10:07:50 am »
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 ?
 

Online janoc

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Re: Hiss with AC-DC buck supply: how shielding ?
« Reply #74 on: December 15, 2017, 08:19:44 am »
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).
 


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