Tonepad DS-1 -- Whining sound?

[isher1992]

I checked all my solder joints, no cold ones.

It doesn't matter what power supply I use, it's still there, effect engaged or not.  It sounds like a high pitched whine/squeal.  Is this a grounding issue?  I have the DC jack, switch LED, and PCB grounded to the input jack at one point.  The Output jack has no ground going to the sleeve, just the input.

Would running a ground wire from input to the output jack solve this?

[MrStab]

does the effect still pass signal, despite the whine? does the Gain/Distortion pot affect the whine?

[isher1992]

Yes, it passes signal when engaged and bypassed.  The gain knob has no effect on the whine.  Neither does the tone control.  The volume knob seems to.

[MrStab]

which version did you build, the TA7136P or the TL072 one?

one approach would be to make an audio probe ( http://www.diystompboxes.com/pedals/debug.html ), check signal at the Emitter of Q1, see if it gets to the Collector of Q2 okay, then see what happens when you reach the other side of C2 and the whole op-amp area. Ofc, the oscillation could be happening as early as Q1.

suggestions include temporarily shorting the un-named 100k resistor just before the Gain pot (i THINK it's sandwiched between C3 & C4 on the layout), seeing if that affects the gain by the minimum being reduced to 1, and also generally checking resistor values in that region.

by "It doesn't matter what power supply I use", you do mean you've tried just a battery too, right?

[isher1992]

No, I hadn't tried a battery, but I have tried an isolated power supply and a non-isolated.

I feel embarrassed to say, the noise was actually coming from a totally unrelated part of my effects chain.  It was normal noise and hiss from distortion layered on top of power supply noise from another pedal!

There was also an issue with the bypass switching, it wasn't wired with the input jack to ground properly.  I used Tonepad's switching layout this time and that solved a lot of the noise problem.  I think a lot of the noise is coming from this newer JRC4558D opamp.  They seem to have a lot of hiss.

[MrStab]

Glad you found the cause! don't be embarrassed, on the upside you've identified that your pedal is fine and that maybe another could do with some better power supply filtering. plus all debug experience is good experience. win-win!