How to make quasi complimentary MOSFET buffer really symmetrical? For BJTs there is a known solution, the Baxandall diode. But MOSFET GS voltage drop is not constant and can't be simulated by silicon diodes, zeners, LEDs etc.
Why don't put another one MOSFET at the same conditions as top one outside of quasi complimentary feedback loop to create exactly same voltage drop? That can't be so simple. Did I miss something?
Why don't put another one MOSFET at the same conditions as top one outside of quasi complimentary feedback loop to create exactly same voltage drop? That can't be so simple. Did I miss something?
This is interesting but waiting for comments from one of the masters of amp design to chime in. You may need 220R gate stoppers between BJT collectors and MOSFET gate to prevent oscillation. Usually a TO126 like KSA1381 and KSC3503 is used to drive MOSFET gate. Although I have seen TO92 JFETs drive a big TO220 or TO246 MOSFET directly before.
Here is an experiment with diamond-like configuration: https://raw.githubusercontent.com/e-asphyx/ltspice_stuff/master/Buffers MOSFET.asc
Here it almost the same LTSpice file as mentioned in post above https://raw.githubusercontent.com/e-asphyx/ltspice_stuff/master/Symmetrical QC.asc
As you can see, at least with properly matched components, current swings are symmetrical with any load (I always try standard headphone impedances)
It appears sound to me. Alex Nikitin in 2006 did something similar which had good performance and was free of cross-conduction. It replaces a Baxandall network and phase inverter with a Sziklai pair which is problematical at switch off.
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I have designed simple headphone amp to test this idea. I named it "Odd Man Out" referring to third MOSFET. Will order PCB soon.
View attachment amp.pdf
View attachment board.pdf
View attachment amp.pdf
View attachment board.pdf
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Nice design. Although to test concept something really simple like just 4 transistor preamp front end might have been enough and done on solderless breadboard. Let us know how it works.
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