I recently bought a Peavey Classic 30. I like the amp but it has a problem. On either channel, with the channel volume all the way down, a slightly muffled clean tone signal comes through. On the overdrive channel, the clean signal persists (staying at the same volume) as I turn up the channel volume, giving me a mix of clean and dirty, which is not good IMO. Once you get to about 3 or 4 you can’t discern the clean sound anymore, but the amp is then too loud for most home use.
Last night I pulled the chassis and did some minor tests, stuff I could do without removing the PCB, using only my multimeter.
here’s the schematic http://www.bustedgear.com/images/sch...classic-30.pdf
All of the volume controls’ CCW tabs have continuity to ground; all of the cathode resistors and bypass caps have continuity to ground; the capacitors at the preamp power supply nodes seem fine, though I don’t think I have what I need to thoroughly test them.
I tried grounding different signal nodes to see what would make the signal bleed disappear. Only grounding the output of the last preamp stage got rid of the bleed, along with any other signal. Strangely, if I ground out the grid of the last preamp stage, the bleed gets louder. That last stage is a mixer stage and has a 2.2M feedback resistor, and I wonder if that has something to do with the strange behavior.
I’m thoroughly baffled. Anybody have any ideas about what might be causing this?
Last night I pulled the chassis and did some minor tests, stuff I could do without removing the PCB, using only my multimeter.
here’s the schematic http://www.bustedgear.com/images/sch...classic-30.pdf
All of the volume controls’ CCW tabs have continuity to ground; all of the cathode resistors and bypass caps have continuity to ground; the capacitors at the preamp power supply nodes seem fine, though I don’t think I have what I need to thoroughly test them.
I tried grounding different signal nodes to see what would make the signal bleed disappear. Only grounding the output of the last preamp stage got rid of the bleed, along with any other signal. Strangely, if I ground out the grid of the last preamp stage, the bleed gets louder. That last stage is a mixer stage and has a 2.2M feedback resistor, and I wonder if that has something to do with the strange behavior.
I’m thoroughly baffled. Anybody have any ideas about what might be causing this?
Comment