Phase Linear 700 input section question

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taj

diyAudio Member
Joined 2005
Can someone describe to me what's going on in the input section of this amplifier? It looks like a second differential amp in series with the first, but it's drawn a bit convoluted so it's hard to tell. Or is it just a pair of symmetrical diff amps drawn oddly?

I've never seen anything like this.

http://www.audio-circuit.dk/Schematics/Phase-Linear-700B-pwr-sch.pdf

I'm just curious, trying to learn. Thanks.

..Todd
 
It's just two diff stages - one feeding the other. The only weirdness is that Q3's collector goes to ground instead of the - rail. That's a lot of VCE difference. I would have dropped it to the rail.

Two diff stages in front of the VAS adds that much more NFB. And these things were on the hairy edge of stability.
 
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