Noisy volume pot on pedal - what could be the cause? (Timmy OD)

[jjg]

Hi all,

I've just finished building a Timmy overdrive pedal (using the layout on Tagboard). I'm very pleased with the sound, the overdrive is great, just what I had hoped for.

HOWEVER, testing it today I noticed that when I backed my guitar volume off a tiny bit, say from 10 to 9, the signal becomes very noisy (buzzy). When I roll the guitar volume back up to maximum, the noise reduces - not completely, but down to what I would consider acceptable.

It seems there is a threshold that below which if I reduce my guitar volume, then it suddenly gets noisy.

You can't perceive the noise when I'm playing the guitar. When I am not playing, the noise reduces when I touch the strings.

I don't understand why reducing the level of my guitar slightly would suddenly increase the buzzing...

I presume I've done something shonky inside the pedal. Could this noise result from a bad solder joint somewhere? And/or from an earthing issue? Could it rather be something external to the pedal, e.g. noise from the ring main in my house?

Any help gratefully received!!!

Thanks in advance,

Joe

[aron]

I wonder if there's voltage on the pot. Is it a regular, non active guitar? (No batteries in the guitar?). Measure the tip to ground with a meter on the guitar cord end - where it plugs into guitar when the other end is in the pedal. See if there's DC there.
Does the volume pot sound scratchy when you adjust it?

[jjg]

Hey Aron, thank you so much for the speedy reply, you are a total legend. Much appreciated.

Ah ok, I will try that and take the measurement, see if any voltage is coming up through the lead. (I think that's what you mean?)

The volume pot doesn't sound scratchy.

My guitar has fairly hot pick-ups, but it is not active. And the noise effect still occurs when I split the coil. Not sure if that is relevant.

Can't get to do the check right now, but will post back later when I've had a chance.

Thanks again :-)

[thermionix]

The noise that goes away when you touch the strings is normal, that's why guitars have string grounds.  It will be much more noticable when you increase gain with an overdrive pedal.

[jjg]

Thanks, that makes sense.

I don't measure any voltage along the guitar lead, which I guess is something!

(I did notice a strange phenomenon this time is when ONLY the output jack was connected from the pedal to the amp (i.e. no input jack): when I turned the gain up past 3, a whistling sound occurred, which changed pitch as I dialed up the gain. Weird. It stopped as soon as the input jack was plugged in. Perhaps this is just a shielding issue, in that without the input jack being plugged in, the socket provides an open hole into the pedal? Therefore nothing to worry about?!)

[antonis]

Just for fun  , try to short input tip and sleeve ..

[patrick398]

Do you have another guitar you can test it with? I'd also check the input cap since it's there to block DC right? Shooting in the dark as usual...

[Myampgoesto12]

I've had a similar buzzy sound that specifically happens when my volume is backed of, since I started using a daisy chain power supply. I haven't tried using batteries only for proof, but I think this is my issue.

How's your power setup?

[pinkjimiphoton]

partially shorted guitar cable
bad solder on the input part of the circuit somewhere
misbiased transistor will also do that. reverse beta'd and misbiased even more.
not super familiar with the timmy tho.
gotta schematic?
voltages? we can tell more from that.

but first thing i'd check would be all grounds
make sure there's no bridges between the vero tracks, particularly at the ends of the strips
any suspect joints, solder suck 'em or use braid and reheat with a hot iron and fresh solder.

"tap" each component on the board with a sharpie or something, fairly hard. anywhere you hear a noise, expect to reflow the associated solder.

hope that helps