Input signal clipping, need to clean it up...

Started by Vesperado, March 29, 2021, 10:37:31 PM

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Rob Strand

QuoteIf you short Drain and Source on Q3, does the clipping go away? If not, it's not Q3.
Without trying that Q3 short test you are pretty much wasting your time.   If the JFET in the circuit really is a J113 (it might not be) it should work find without clipping.

I'm of course assuming the clipping problem is in Effects mode and not Bypassed mode.
Send:     . .- .-. - .... / - --- / --. --- .-. -
According to the water analogy of electricity, transistor leakage is caused by holes.

iainpunk

#21
Quote from: iainpunk on March 30, 2021, 08:44:09 AM
i recommend you grab an audio probe and check where the distortion starts, i honestly doubt its that first transistor.
cheers
i just want to re-state this:
i honestly doubt its that first transistor.
maybe check with an audio probe where in the circuit the distortion ACTUALLY starts

cheers, Iain
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers

antonis

Quote from: iainpunk on April 03, 2021, 11:28:25 AM
i honestly doubt its that first transistor.

Could you plz keep your opinion to yourself, Iain..??

P.S.
Late night with aged tsipouro here.. :icon_wink:
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

Vesperado

Appreciate the feedback, gents.

Next time I get into the FX68 I will bypass Q3 and raise the Vbias to see what happens. The audio probe is a good suggestion. I agree, I do not think Q5 is culprit here, although I suspected it at the beginning.

The pedal is useable now, yet at any rate it wouldn't hurt to get a non-clipping signal at headroom...and preferable, no doubt.

Vesperado

And while I'm in there I might replace the stock TL062, or cut the trace and lower the Vbias with a trimmer there. It is the only other place I can think of...

Vesperado

Replaced the TL062 on the FX68, which removed the clipping. I have Vbias now set to 7.6V and Q5 at 7V. Good headroom, nice chime :)

Before disturbing the transistor on the 460 I will replace the ICs first. Probably all it needs...