Pearl Octave

Case study in a faulty op amp stage/bad capacitor

Symptom: low effect output.

Method: signal trace.

Clue: Unity gain at IC1A. "Touch-in" a good 10µF cap across suspect C4 and observe good effect output.

Cure: Replace C4.

Why: C4 provides a low impedance ac path to ground allowing R6 and R5 to function as a voltage divider for the negative feedback. Less negative feedback = more gain. If C4 is open, then there is no divider action and we have 100% negative feedback applied. 100% NFB = unity gain.

With the divider action working, gain should be about x4.5.

AVR-1, trim pot for IC6A/D negative feedback, cancels out the fundamental frequency. This is factory set. Adjusting away from the null point blends the fundamental with the octave up. There is only a narrow point where the null appears.

The octave up signal could be a little louder for my tastes. I would try reducing R49 if this was my pedal. This was not a complaint of the customer's.