Hi, I've been refreshing this amplifier over the past year in stages. First the PS then on to the amplifier board. I replace all the the electrolytic caps first and it was so far so good. Listened to it for a few months then decided replace the non-electrolytic caps. The outputs transistors are good but the amp is now oscillating. Being somewhat frustrated now I decided to bring into an audio service center in Chicago that is an authorized repair some very high-end gear and is very familiar with V-fets. Anyway, they believe the problem is with the ceramic caps that I replaced with poly-caps in the feedback circuit that is causing the oscillation. Everything else checked out fine on the amp. So my question is it possible the the makeup of the cap is critical here? Ceramic vs Poly? I don't post much here but I would appreciate some feedback on my situation. Thanks!
The caramics are of very low value intended for high frequency. Low inductance is a must as IIwhtt hints.
Use highest quality ceramics, styroflex maybe, high voltage (100V ++) to minimize voltage modulation of the layers.
Use highest quality ceramics, styroflex maybe, high voltage (100V ++) to minimize voltage modulation of the layers.
Make sure that they are COG/NPO ceramic capacitors.
Styroflex capacitors are wound plastic film types, not ceramic.
Ceramic capacitors work much better than polys for bypass applications. They have much higher resonance than any other type of capacitors.
Poly capacitors are much more linear than ceramics. They belong in filter circuits etc.
I guess you must have read some snake oil that motivated you to do such a foolish thing. Always ask an engineer about such topics.
Poly capacitors are much more linear than ceramics. They belong in filter circuits etc.
I guess you must have read some snake oil that motivated you to do such a foolish thing. Always ask an engineer about such topics.
I see you replaced ceramic caps in the feedback loop. Those caps are put there to satisfy Nyquist stability criteria. High resonance is an absolute requirement for this application.