Clipping diodes?

[msclford]

Check out D101 and D102 next to V2 in the attached image - are these clipping diodes? The amp is a Peavey Valveking.

[msclford]

Sorry - image was too big. Check it out herehttp://www.blueguitar.org/new/schem/...veking_112.pdf

Page 9

[Enzo]

No, they are noise reduction diodes.

Note they are shorted across by the relay or switch in certain settings. The high gain channel is noisier, so they are switched in. But on the clean channel, noise is less an issue and they are shorted across.

In any case they can't clip the signal there.

CLipping diodes would typically be from signal to ground, not series like these.

[msclford]

I see. I'm an amateur hobbyist (if that), so I don't really know much about these things. I just recognized something similar when I was working on a Tube Screamer once. I really appreciate everything I learn from everyone on this board, though.

Another thing - can anyone suggest a good way to learn a few things about electronics, perhaps a book? Classes are a little out of the question right now, since I'm already taking classes in another field. What kind of credentials are needed to work as an amp tech, or just to work in a repair shop in any way? I'm really interested in tube electronics and guitar-related work.

[cbarrow7625]

I read an article at one point where one of the Peavey amp designers was being interviewed and thes noise reduction diodes came up. His basic explanation of how they reduced noise was that when no signal is present, all that is trying to get passed through the amp is background noise and hiss. At the point in the circuit where the diodes are added, the background hiss is less than 0.6V (the forward voltage drop of the diode). Since the noise level is less than the required forward voltage drop, no signal passes through the diodes. As soon as a note is played, the signal voltage jumps up to many volts and passes pretty much unaltered through the back to back diodes (one passes the positive halves & the other the negative halves of the cycles).

He described it as a poor man's noise gate, which it basically is.

I did try jumpering around these diodes in a different hi gain Peavey amp some years ago and found that there was a minor tonal shift with the diodes in or out. With the diodes in the sound had a mildly "harder edge" to it and was a litte softer with the diodes shorted. I preferred the sound with the diodes in, so I left it alone. But that probably explains why they switch them out for the clean channel. There must be a little bit of crossover distortion going on when the positive & negative halves of the cycles transition from one diode to the other (I can't imagine they take thetime to perfectly match the characteristics of the diodes.)

Chris