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Diff amp balanced?

> First things first, I measured only the front end stages...
> I found no measurable un-balance with CCS cathode load diff amps. i don't give them any NFB input

I just realized what you're saying.
You are correct on one point. Without feedback, a differential stage with CCS on the cathode is perfectly balanced.
Your mistake is to assume that the balance is maintained when you close the feedback loop.
Measure with feedback... Imperfection redefined. Been there, done that!

A single diff-stage just won't cut it! Try adding loop gain, but then you have to accept lots of NFB. Not that ideal!
You're not alone here... Some commercial "upgrades" assume the EXACT SAME FAULTY ASSUMPTION OF PERFECT BALANCE...



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