Buffered output Wah oscillates - but not everywhere

[Lino22]

Antonis the pop is caused by oscillation, this is not the leaked DC pop.
My setup is guitar/or nothing > wah > amp.

[antonis]

Antonis the pop is caused by oscillation, this is not the leaked DC pop.

If so, it leads in oscillating buffer..

I'd try a BJT based buffer (don't worry about buffer's input impedance for the moment) of low output impedance..
(about 5mA working current should be OK..)

P.S.
I still can't see any obvious reason for using a buffer in the output of a Wah pedal but it should be "academically" interesting to find the cause of your issue..

[Lino22]

Yes, BJT was gonna be my next move, i will report back.

[GibsonGM]

I'd like to see the pop on a scope.  Or, can you make an audio clip of it?

[anotherjim]

The buffer is so the wah works with low impedance loads such as FF, but a 10k-15k in series with the output to the jack tip works well too if you don't mind a little level drop.

[Lino22]

I'd like to see the pop on a scope.  Or, can you make an audio clip of it?

Good call, here you are. 1.33MHz, but amplitude modulated by something i can hear.

[antonis]

Probably I'm wrong but it seems to me like oscillation due to positive feedback via Gate to Source capacitance..

Could you try a 1k or so resistor in series with JFET Gate..??

[anotherjim]

That's what I was seeing. Where did you try adding a cap?

[Rob Strand]

That's what I was seeing. Where did you try adding a cap?

Also, look at the waveform when you have the added caps in place.

Could you try a 1k or so resistor in series with JFET Gate..??

And a 1k in series with the output lead.   Perhaps see if pulling the output jack,
which will remove any load capacitance, affects things.

I suspect the oscillations are there *before* be buffer.   However, you might
find placing a x1 CRO probe can stop the oscillation, so you need to do measurements
before the buffer with a x10 CRO probe.   A way around that might be to look
for oscillation on the output of Q2's emitter.

[Phend]

Mechanical fix:
Put in a stop so the pedal won't go down so far.

[GibsonGM]

Mechanical fix:
Put in a stop so the pedal won't go down so far.

Or mess w/the R across the wah inductor to adjust the Q a little (trim pot?).  I'd like to HEAR the problem.  Every wah I've ever messed with needed something done with the "33k" across the inductor, to be honest.  Adjusts honkiness.

[Lino22]

Mechanical fix:
Put in a stop so the pedal won't go down so far.

... or maybe when the fellow starts quacking i'll say don't do it. 

Thank you guys, i am pretty sure the solution is at the door. I will have time to deal with it tomorrow, and report back.

[Lino22]

That's what I was seeing. Where did you try adding a cap?

I tried 47p between the wiper and ground as well as across the 10k emitter resistor.

[Lino22]

Probably I'm wrong but it seems to me like oscillation due to positive feedback via Gate to Source capacitance..

Could you try a 1k or so resistor in series with JFET Gate..??

Yes, this may be it, i will definitely try it. Thank you. Or as Rob says one serial 1k at the output - it creates a low pass filter with the cable if i am not mistaken. And my coil cable audibly makes it less loud.

[Lino22]

Heureeeeka! Sorted.