Distortion on bypass

impmann · June 2014

Help!

I've just bought a lovely old Ibanez SD9 Sonic Distortion pedal - it all seems great, except when in bypass notes don't decay cleanly. It's a similar age pedal to the classic Tubescreamer TS9 perhaps someone has had similar with one of these?

Any ideas - I don't want to send it back, as they aren't exactly common...

Thanks!

Johnnyseven · June 2014

This may not be exactly what you're after but i'm pretty sure the 9 series can be modded for true bypass if you can't get the buffered bypass to sound right.

impmann · June 2014

Thanks - but it's not quite what I want to do with this.
Anyone have any other ideas?

ChrisMusic · June 2014

Simple loop switcher to put the SD9 in and out of circuit. They are often on here cheaply, or make your own.

Doesn't solve the pedal issue, but would make it useable if you like the SD9, and it might come in handy later for something else.

ICBM · June 2014

If it's leaking distortion into the bypass signal like the standard problem with the Boss SD-1, running another buffered pedal immediately before it will probably stop it. Not a 'fix' I know, but it might be a simple solution.

The fault may be caused by failing electrolytic caps, they're getting to that sort of age now in a lot of older pedals.

impmann · June 2014

Brilliant @ICBM that 'fixed' it.

What is the root cause of that? I'd like to fix it properly... I also noticed that when the output cable is attached to an amp and nothing is plugged into the input there is an excruciating high pitched whistle.

Thanks for all the help so far.

ICBM · June 2014

I think the problem is caused by the distortion leaking into the input buffer via the V/2 supply. It definitely gets into the audio path there, which is why running a buffered pedal before it 'fixes' the problem - by essentially shorting the leak to ground via the very low impedance of the output buffer before it. I have actually tried fixing it on SD-1s by improving the filtering, but never with 100% success, so it may be inherent to the pedal rather than a fault - I can't remember the last time I listened closely to a Sonic Distortion, although I owned one some years (… cough… decades…!) ago.

The whistle is because the input isn't grounded when no cable is in the jack, so it acts as an antenna.

impmann · June 2014

Thanks, mate.

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Distortion on bypass

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