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Re: Since you asked...

Charles,

I don't know if what I described qualifies as NFB but that's probably a semantic dead-end. What I'm thinking of has no forward gain and there's no virtual earth but, anyway, I was curious if you'd tried it. On a related topic, I've been toying with a power amp design and set myself a goal to make it as simple and linear as possible without any overall NFB. I'm going for a diff pair voltage gain stage and balanced follower outputs - hence my interest in the follower related threads. From what I've read about your amps they are simple (not many stages) and have no overall NFB and are balanced.

From a circuit design point of view one limitation I see is the finite output resistance of the diff pair stage driving the output power FETs - the non-linear input capacitance sets the distortion limit. An obvious thing to do is to add a second set of followers to buffer the voltage gain stage from the output stage and that improves things as expected. However, I recall a review of one of your amps where bandwidth was discussed with comments from you that the limitation is in driving the input capacitance of the output power FET followers. You tried adding a buffer which improved the bandwidth as expected but the sonic performance was much degraded. As the bandwidth without a buffer was adequate, if not stellar, you left it alone for superior sonics. I'd be interested any comments or advice on driving followers simply.
Can you really 'design' it well or do you just have to build & tweak ..etc.

TIA
13DoW

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