Power supply and leaking signal

[Marbles]

Ok, this is going to sound weird, but maybe there is an explanation.

I have had a few instances when my pedals were 'off', but the (for instance) volume control had an effect on my signal.

Ofcourse the most logical explanation is: The switch is wired incorrectly, and I made a mistake.

It has happened with 2 pedals and I checked everything and it worked perfectly fine in other instances. I could not reproduce it.

Now it got me thinking: I have had problems with a Boss HM-2 (the original pedal) being not able to be powered off, light kept burning. Another pedal has had that problem as well.


So it's not a debugging question, but just for my understanding: Could a problem with a powersupply have any effect on the signal passing through it whatsoever? I know it shouldn't, but could it?

I use a voodoolabs pedalpower in a house that does not have any grounding on the sockets.

[Frank_NH]

I had a "weird" instance like this recently (perhaps not your exact problem).

I was developing a tube screamer circuit, and had a basic TS circuit on my breadboard (see below).  I was noticing that when my volume was fully off, there was still some signal coming through, as if it didn't turn off!  I checked every connection and it seemed OK.  Then I noticed...there is a 47 uF cap to ground on the power section where the reference 4.5V supply is formed (as in the schematic).  The volume control is connected to this reference voltage.  I had forgotten to add this cap to my breadboard, and when I did add it, the problem went away.  Apparently that cap is there to prevent signal oscillations from affecting the reference voltage source (effectively damping them out).

So, yes the power supply components are very important, and making sure you have stable supply and reference voltages is key to reducing noise and unexpected effects such as the one I encountered.  I also believe that some of the high pitched oscillation you get with some high gain distortions may be due to a combination of layout and poor power filtering.  Perhaps for my own designs I may experiment with using an op amp to supply a stable reference voltage versus a simple resistor voltage divider.  Perhaps overkill, but...

[Marbles]

Thanks for your reply!

It was the screwdriver for me. I'll open it up and check what's wrong with it. The controls actually effected the signal when the effect was off. My clean was muddy and I couldnt figure it out. Turns out the controls had effect on my clean signal. With your explanation, that must be an error on my side, because so many effect is not possible I guess..

It may explain however the effect the noise swash had I think. That one has some oscillations controls and the effect was actually oscillating in the background when turned off. I'll have a good look if I can fix that without making it less crazy.. Thanks!