I've rebuilt a defunct Stasis 3 amp with blown outputs on one channel. I replaced the outputs in both channels with MJ21195/MJ21196. I recapped and replaced the transistors on the input board. I used the same type of transistors except for the diff pair, for which I used ZTX696a. However, any attempt to replace the 2sa1112/2sc2592 pre-drivers with a variety of subs resulted in immediate oscillation.
A 10k square wave into 4 ohms showed significant ringing, but no overshoot. The ringing was much worse without a load. I replaced the 39pf base-collector mica's on the pre-drivers with 100pf with improvement. Then finally 200pf micas eliminated most of the ringing.
Am I going about this correctly?
I've attached pictures of the 100pf and 200pf scope outputs.
A 10k square wave into 4 ohms showed significant ringing, but no overshoot. The ringing was much worse without a load. I replaced the 39pf base-collector mica's on the pre-drivers with 100pf with improvement. Then finally 200pf micas eliminated most of the ringing.
Am I going about this correctly?
I've attached pictures of the 100pf and 200pf scope outputs.
