Phase Linear 700 input section question

taj · 10th July 2009, 03:51 PM

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/Schemati...0B-pwr-sch.pdf

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

..Todd

wg_ski · 10th July 2009, 05:24 PM

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.

10th July 2009, 03:51 PM	#1
taj diyAudio Member Join Date: Feb 2005	Phase Linear 700 input section question 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/Schemati...0B-pwr-sch.pdf I'm just curious, trying to learn. Thanks. ..Todd

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10th July 2009, 05:24 PM	#2
wg_ski diyAudio Member Join Date: Oct 2007	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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