Return of my differential VAS

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PMA

PMA

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pmacura.cz/audiopage.html
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Started to play as well ... :D
 

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scott wurcer

scott wurcer

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Joined 2004
bear said:
I think I have seen this circuit before... not quite sure where at the moment...

Btw, what was the purpose of the 2k resistors between the jfets?

Trying to follow along in my Libretto... ;)

_-_-bear
Click to expand...

More nodes with "infinte gain" than degrees of freedom. For a particular set of device offsets the DC solution is singular in simulation as well as in reality :) . The 2k resistors allow some differential current to flow when you use current mirrors.
 
scott wurcer

scott wurcer

R.I.P
Joined 2004
Steve Dunlap said:



It is possible you have seen this before. A very similar circuit was published in 1990 by William C. Snyder in "Class A Audio Design".
Click to expand...

As I stated the first time it's was an attempt at a complimentary version of the OPA627. Once you realize the self biased FET's can substitute for the LTP's you can go through and "Muntz" away. I think the first use of this CMFB was by George Erdi at PMI in the 70's. I happen to like this better than the one transistor mis-matched resistor take off, which BTW I don't consider truely full complimentary symmetry. The top and bottom transistors act like an LTP with one side pnp and the other npn.
 
Steve Dunlap

Steve Dunlap

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Joined 2008
scott wurcer said:


As I stated the first time it's was an attempt at a complimentary version of the OPA627. Once you realize the self biased FET's can substitute for the LTP's you can go through and "Muntz" away. I think the first use of this CMFB was by George Erdi at PMI in the 70's. I happen to like this better than the one transistor mis-matched resistor take off, which BTW I don't consider truely full complimentary symmetry. The top and bottom transistors act like an LTP with one side pnp and the other npn.
Click to expand...


Hi Scott,

I wasn't trying to imply anything here, just pointing out why the circuit might look familiar to Bear.

"As I stated the first time it's was an attempt at a complimentary version of the OPA627."

Remember, I'm relatively new here and haven't gone back and read all the older threads. Apparently I missed the thread were you stated that the first time.
 
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