Tube DIY Asylum

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Re: Cathode Feedback

Posted by Triode Kingdon on January 27, 2004 at 10:20:44:
Well, now you're stretching my memory. However, I think I tried cathode FB alone, not with NFB. I was hoping it might serve as a non-global substitute. In the end, I decided the amp sounded pretty good with lots of NFB, so that's what I used.
I'll add that I think NFB is generally unavoidable with pentodes. All my pentode amps (PP and SE) exhibit an odd sound when NFB is removed, a sort of paper-like rubbing sound or breathing underneath complex tones. I think it's due to IM, but that's just a guess based on some tests I performed many years ago (produced the same sound). Unfortunately, I no longer have an IM analyzer. :(