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Old 15th December 2012, 09:38 PM   #1
diyAudio Member
Join Date: Dec 2012
Location: Dallas
Default Recompensating a Stasis 3

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.
Attached Images
File Type: jpg 100pf.jpg (477.3 KB, 70 views)
File Type: jpg 200pf.jpg (488.2 KB, 66 views)
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