How to reduce power supply noise without losing voltage?

[Deceiver]

Hi there,
this is my first post here. And I am quite new at this too, building stomp boxes for about half a year and some change. I have encountered a problem that surely has a simple and elegant solution, but I was unable to find it on the internet. Building a Shoe Pixel clone now and it gives an unpleasant hi-pitched noise from the power supply (it is fine with battery), especially when the guitar is muted. Adding a simple power filter with diodes and capacitors helps a bit, but there is a significant drop of voltage I would like to avoid.

My idea is that if there was a simple and functioning circuit that would do the job, I would add one to every similar stomp box I make. I plan to build personalised stomp boxes for my friends and band members, as a gift or as thanks for something... and they, being punks they are, usually don't have a fine filtered power supply, so this would be a great solution.

And... I don't know if it's even worth mentioning, but don't be overly technical please. I teach humanities and I've rarely encountered electrical engineering before. I learned a lot from building my first pedals, but I am an absolute newbie nevertheless

Thank you very much!

[11-90-an]

Hi and welcome to the forum 

For reverse polarity protection with minimal voltage drop...

http://www.geofex.com/article_folders/cheapgoodprot.htm
http://www.geofex.com/article_folders/mosswitch/mosswitch.htm

For power filtering, (disregard whatever diode you see since above circuits take care of that...)

https://www.diystompboxes.com/smfforum/index.php?topic=125422.0

[R.G.]

Not all 9V power supplies are created equal. Some of them are very quiet by design and long efforts to keep them that way, -others are just - um - without special low noise design features. This does not always correlate with price. At least one very low noise 9V supply exists that was designed specifically for powering finicky 9V pedals, and costs US$20 - 25.

You can get very low noise by using a power adapter that puts out more than 9V, then using a simple regulator circuit as well. If you are interested in this approach, we can supply links to regulator circuits.

[PRR]

A power filter is often a resistor-capacitor filter. Diodes are more for reverse blocking.

The voltage drop depends on resistance and current. If Ohms Law is verboten, try 10 and 100 Ohm series resistors and figure what would make a "small" drop (often about a half-Volt).

Knowing R and frequency and required attenuation, it is possible to calculate a good C. But in today's world, just throw 100uFd at it.

High frequency whine can be much easier to filter with low drop than hum/buzz. (But whine also leaks more.)

[Rob Strand]

It's a multidimensional problem.  You need to pin down what you are dealing with.

There's switch-mode vs transformer based supplies.  Different problems arise with each and different solutions are require for noise issues.

Wiring and the presence of on-board DC/DC converters and charge-pumps are another factor.

Based on the whine and the circuit I'm assuming:
- low current pedal
- switch-mode power supply.

A switch-mode power supply can produce whine if the load is too small.   This can happen when powering a low-current pedal.   It would be wrong, and solving the wrong problem, if the power supply is whining due to light loads and you are trying to patch it-up by filtering the DC.   The solution here is to put a dummy load on the power supply.  A load of 1/10th supply rating is a good start but you should definitely try to back off the load as much as possible.

Assuming it's not that then it is likely the HF ripple on the supply is too high.   That can occur on old PSU's that are about to fail.  Assuming it's not that then a DC filter can work.   For the lowest voltage drop a LC filter using an inductor and cap would work.

This came-up a few months ago.

https://www.diystompboxes.com/smfforum/index.php?topic=125422.msg1194134#msg1194134


LC filters have low voltage drop at DC.   Lower than RC filters.

An LC filter on the PSU will help stop noise from the PSU getting to all devices connected to it.   A local RC filter (or LC filter) in the pedal can fend-off some degree of noise from the PSU.   If you power multiple effects from the same supply, filtering the PSU is better because you know that's the cause of the problem.

[bluebunny]

Welcome!

it gives an unpleasant hi-pitched noise from the power supply (it is fine with battery)

Sounds like the power supply is the culprit, doesn't it?  What is it?  The advice about RC filters and protection is all sound, of course, but we might as well fix the problem at source.

[Elijah-Baley]

Sometime I asked about the inductor used in the power supply filter, it has to go in line to the 9v. I finally bought a 680uH inductor, and I have to try it in a pair of fuzz circuits I built: Foxx Tone Machine variation and Woolly Mammoth. With both I got a whine noise if I use my old Boss PSU, that usually works fine and noiseless with all pedals I built.

I told this story sometime here and there, but nobody told me if the inductor is the final solution to this kind of issue.
The inductor should drop less voltage than a resistor but even could filter better noise and whine, (and don't forget 47/100uF cap across the ground). I'm waiting to get less busy to try this trick.
In the Woolly Mammoth, especially after some mods to make it more guitar friendly, I can hear a bit of whine at high volume with at high gain and open tone controls. (It was ok with battery.)
The Foxx Tone Machine is more problematic. I got some months ago the whine tamed just using a 330R resistor in line. I couldn't hear too much difference in the sound, but a 330R seems to me very big.

[Deceiver]

Thank you very much for every suggestion! And also for your warm welcome

I would like to solve the issue on the pedal itself, mainly because this thing seems to appear only in basic designs using only transistors... Everything I made or experimented with that uses ICs works swell.

I have, if you would be so kind, few questions, majority of which are sort of educational for me, because thanks to you I think that I know what the problem is

1) 11-90-an mentioned reversed polarity protection. I use a reversed diode for this, it was already designed with it (and this design also has a filtering capacitor of 100uFs, as can be seen in link below...). The drop of my own filtering circuit that I added before this was large (I suspect) due the combination of another diode i put there in series and another resistor I added between my two filtering capacitors... so, my question is: what is the function of the resistor here? I see that there is one 200r even in the circuit itself... has it anything to do with filtering? Wouldn't it be possible just to get rid of it?
And the most important thing for me: wouldn't it suffice just to change the value of the filtering capacitor right on the vero of this effect itself? To change 100 uF to 470 uF for example?

2) Also, I tried to build a capacitance multiplier to help me with filtering, using one NPN transistor, because I've seen it on youtube... what is even an upside of this? It cuts voltage like hell (around 0,6-0,8) and works worse than any other solution

2)

A switch-mode power supply can produce whine if the load is too small.   This can happen when powering a low-current pedal.   It would be wrong, and solving the wrong problem, if the power supply is whining due to light loads and you are trying to patch it-up by filtering the DC.   The solution here is to put a dummy load on the power supply.  A load of 1/10th supply rating is a good start but you should definitely try to back off the load as much as possible.

This caught my attention! It is true that this whine appears only sometimes on some circuits! Haha... and I just realised that when I daisychain my reverb pedal with this effect, whining stops!!! So I think you nailed it Even with no load here the whine appears only in the "soft mode" that is lighter and has in fact a large volume drop from the "hard mode" (it was designed by Shoe this way).
So my question is sort of daring... but of the most importance for me in this post so I underline it ... forget the filtering for a minute... how could I tweak this effect to make it a bit more current consuming? Ideally to make the effect in "soft mode" louder (a unity with "hard mode" would be swell!) I will experiment with values, but I would like to know with which value I can experiment, and what I need to change here. I've already built it so I would need to know the parts, so would anybody be so helpful to look on it and tell me?

Thank you very much. And again, I am surprised by the amount of good will on this forum, you made my day

Here is the circuit itself on vero, I've built nearly identical one
https://tagboardeffects.blogspot.com/2017/09/shoe-pixe.html

[Rob Strand]

This caught my attention! It is true that this whine appears only sometimes on some circuits! Haha... and I just realised that when I daisychain my reverb pedal with this effect, whining stops!!! So I think you nailed it Even with no load here the whine appears only in the "soft mode" that is lighter and has in fact a large volume drop from the "hard mode" (it was designed by Shoe this way).

You probably have both types of noise.

So my question is sort of daring... but of the most importance for me in this post so I underline it ... forget the filtering for a minute... how could I tweak this effect to make it a bit more current consuming? Ideally to make the effect in "soft mode" louder (a unity with "hard mode" would be swell!) I will experiment with values, but I would like to know with which value I can experiment, and what I need to change here. I've already built it so I would need to know the parts, so would anybody be so helpful to look on it and tell me?

You could do it.   Where the jack enters the pedal just put a resistor across the incoming jack terminals.

I guess the problem with that is if you had 5 low power effects that need to pull a reasonable amount of power, the wasted power starts to add up.  Better is to make a dummy load which has a DC jack with a resistor.   You plug the supply into that load at the start of your daisy chained power.  That way there's only one load which you can easily tuned and has no impact on any of the pedals. 

If you were going to make a filter which filters all the power then you could build a filter box and put the dummy load in that box as well as the filter.

[duck_arse]

always nicer when the poster provides the info, layout, circuit dia, but hey-ho. here, see, your layout and "A" circuit. the cap shown on the circuit diagram as C1 is in the wrong place on the parts layout, and won't work against the 200R resistor as a filter as intended. you can amend your layout by shifting the C1 leg currently going to the +9V line down to the row with the 200R and 200k resistor attached.

shift that cap, let us know if it works, and also welcome to the forum.

[Deceiver]

always nicer when the poster provides the info, layout, circuit dia, but hey-ho. here, see, your layout and "A" circuit. the cap shown on the circuit diagram as C1 is in the wrong place on the parts layout, and won't work against the 200R resistor as a filter as intended. you can amend your layout by shifting the C1 leg currently going to the +9V line down to the row with the 200R and 200k resistor attached.

shift that cap, let us know if it works, and also welcome to the forum.

Sorry for not posting pictures and thank you for providing them! I did the thing you mentioned... but changed 100 uF to 470 uF just to be sure. The result is that it works pretty much as advertised There is still some noise in easy mode when Pinch knob is up, but it is comparable to other pedals I own... and hard mode and now even lower values of pitch on easy mode are without any noise whatsoever, the effect does good job cutting out everything, be it from pickups or source.

The squeal that was loud before is still here, but so quiet it doesn't matter, it doesn't bleed into signal anymore... and I am pretty sure that it has everything to do with the fact I use switch-mode power supply.

Here it is how it looks now. This vero is pretty messy, because I didn't get right values of resistors and now it is pretty hard to get anything, because my country ordered a curfew. There are three resistors instead of one in one case



I have still some questions, but I think it would be better for other topics since it has nothing to do with the power supply. So... thank you all again!