- Feb 18, 2018
Sometimes high gain amps have negative feedback loop between pre amp stages. If there is and you have cancelled stages perhaps it has turned to positive feedback which can cause oscillation?
Well, it started out as a very low gain amp. There are technically 3 gain stages in the stock PA 100. Similar to a BF/SF amp in that respect. But even with the stock master volume and the first small mods I did to the inputs and cathode values, it was still a very clean pre-amp. That's when I decided to cascade the first channels (V1A and V1B) and convert to a cathode follower driven tone stack. I guess I just figured that it wouldn't make this much of a difference, even with V5 still in the circuit. Since I set V2 up similar to a Marshall JCM 800, I really failed to take into account the added gain stage of V2A, in addition to the less loading of the tone stack. There's just too much gain. More than a very high gain amp. And that's not really what I want. If I can lessen some oscillation just by reducing gain (taking out a gain stage), then I should do that next. My plan was never to make a super high gain amp. I just wanted it to be like a JCM800.