ADA Preamps > MP-2

Only high gain voicings working

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Thor:
Dug out my old MP2 and only the high gain voicings work; all of the clean and vintage voicings there is no sound passing through. Also seems a bit noisier than I remember. Tried swapping out the tubes to no avail. Any ideas where the problem may be?

MarshallJMP:
Do you feel that the high gain is really high gain, or do you feel there is gain loss?

Thor:
They still seem like proper high gain voices, though perhaps the Input control needs to be juiced a bit more than before. It's been some years since I last used it so I can't recall if this was always the case.

Thor:
I've done a bit of troubleshooting and confirmed the signal makes it as far as pin 2 of U302 (input of 2nd tube stage) in the clean voicings, but there is no signal at pin 7 of U300 (input of 3rd tube stage). The plate voltage at pin 1 of U302 also measures 190V for clean voicings and drops to 155V for high gain voicings, while the other three plates maintain voltages around 130-134V for all voicings. Cathode voltage at pin 3 of U302 is 21.3V for clean and 21.8V for high gain; grid voltage at pin 2 is 17.5V for clean, 20.7V high gain.

Thor:
So it turns out it was a bad Q311, which luckily is a super common 2N3904 I had a replacement for. Now time to clean all the jacks, pots and switches  ;D

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