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Preamp plate voltage and tone circuit clipping

Messages
1
I've built a Princeton Reverb (AA1164) and am getting clipping right after the first capacitor of the tone stack (250pF). I'm measuring a plate voltage of 196V off pin 1 of V1 (7025), the first preamp stage, and the schematic calls for 160V. The sine wave is unclipped going into the capacitor, but comes out of the capacitor clipped on the positive side of the wave. It also looks like a 2nd-order harmonic has been added to the sine wave as it comes out of the capacitor. My questions:

1) is the clipping due to the high plate voltage?
2) if so, how can I get that voltage down?
3) if not, does anyone have any ideas where the clipping is coming from? Needless to say, it propagates through the circuit to the output. Sounds great, except for a little ghosting in higher registers, but I need to play clean every once in awhile!
 

pdf64

Member
Messages
8,151
I think you may be overdriving the 2nd stage; that will happen when the signal level is such that the (instantaneous) grid voltage attempts to become positive with respect to its cathode.
I guess that the volume control is set very high, perhaps at max? If so, turning the volume down some should get rid of the clipping.
 

Blue Strat

Member
Messages
30,243
What's your signal level going in and out of that stage? Lift the end of the coupling cap toward the second stage and look at the signal again. It'll probably be unclipped which proves that the first stage has nothing to do with the clipping.
 






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