Schaller Tremolo Repair

[dperry]

Hi all,

I have a Schaller tremolo that needs repair.

Almost overnight it developed a lot of white noise in the background, even when the effect is not turned on.  As soon as the pedal is in the chain it generates white alongside the signal.  I have checked all the ground connections and they all buzz out, and I have tried powering it with a few different psus and batteries - it does the same on all of these.

It was bought in the 90s, so I suppose it's not really vintage, and none of the caps look like they've leaked. 

How would one go about tracing the issue ?

Thanks

[kaycee]

Is it true bypass I wonder? If it is then I'd look at reflowing the switch and jack connections as they are all that are common in on and bypassed state.

If it isn't true bypass, then my distinctly uniformed guess would be Q2 introducing the noise, either through poor connection or gone south.

[JerS]

Audio probe the circuit to see which part of it is adding the noise. Although after looking at the schematic, I would target Q2 as a possible source since it is really the main active component in the signal path.

[dperry]

Is it true bypass I wonder? If it is then I'd look at reflowing the switch and jack connections as they are all that are common in on and bypassed state.

If it isn't true bypass, then my distinctly uniformed guess would be Q2 introducing the noise, either through poor connection or gone south.

As far as I am aware, it is not true bypass - the signal does not pass when the unit is off and there is no power applied.

Thanks for the help - I will look at Q2 - the existing trannies are all bc549c - I don't think I have any spare of those, would a 2n5088 work? Or any other NPN for that matter?

[MikeA]

Thanks for the help - I will look at Q2 - the existing trannies are all bc549c - I don't think I have any spare of those, would a 2n5088 work? Or any other NPN for that matter?

Yes, a 2N5088 or pretty much any NPN should work. Just watch the pinout, the BC549 and 2N5088 pinouts are opposite.  And you're right, this unit is buffered bypass, so it's the output buffer transistor that's most suspect since it's always in the circuit.  It could be one of the others, but not as likely.

[dperry]

You guys were right

I swapped out the Q2 BC549C for a BC549B and now it works as good as new.  Thanks!