This is very promising CF circuit, distortion is most certainly very low. Somewhat overdone circuit, a bit more complicated than necessary, and finding J and K output mosfets specified is now difficult. But I like it, too.
BTW, I think that your proposal from other threads to use inverting input in VF amps has some merit and should be examined in more detail. At least, with power amps, it is easy to solve the problem of absolute phase by inverting connections at one side of loudspeaker cable. A number of people reported that VF amps sound better when inverting mode is used. Few years ago there were many amps with power ICs that used that kind of circuit. And John Linsley Hood promoted idea of using shunt feedback in MM phono RIAA stages as better sounding in spite of having 10dB more noise.
Is this some kind of trick question? I am not EE, and circuit is drawn in such way that it is somewhat puzzling to me.
Clearly CFA. Q11, Q12 are simply just bias providers for Q3, Q4 tracking cascodes. Nothing special about the circuit, only to complex for resulting performance. A big question remains how it would sounds, so build and listening test is of utmost necessity.
Dadod, what I would do on last sch is to leave BJT pair at the input, cascoded with j-fets, BJT VAS/TIS with 470 ohm base and 10 ohm emitter resistors and no gate stoppers at output mosfets. Compensation with smallest possible Miller caps and remaining necessary cap compensation to GND or to OUT, just enough to stabilize it.
In latest schema I see you use TMC error correction - symmetric.
I have tried this in simulation for a current fb amp similar to yours.
It works well and lowered distortion with 12-13 dB.
Thanks for asking dadodI've got only 2dB at 20kHz lower distortion. I think this VAS/TIS has to low gain to get more. Could you show your circuit?
This confirms the magnitude improvement is like 13-14dB, with TMC.
Indeed it is.
I did this compensation calibration by measuring 3 MHz signal and rotating all four trimmer caps, so I manage to find the sweet spot that amp was stable and without distorting 3 MHz sine signal. It was really easy.
Thanks for asking dadod
I took VSSA and squeezed it. Then I squeezed it a bit more ...
Yes, I think my circuit has more OL gain.
Because I have to use like 220p for compensation.
Without TMC it has THD 0.00175%
With TMC it has THD 0.00037%. Both at 1 Watt 1kHz 8 Ohm.
At 25 Watt it has THD 0.00031%
As you can see TMC is best at 470p, 470p, 1.2k in this circuit.
Usuallý C3 is 3-5 times bigger, but not in this case.
My amplifier is targetted to give at least 25 Watt RMS at 2x25VDC.
I have another circuit which has even more gain and less distortion with TMC.
It uses darlington VAS = two transistors at each half.
Otherwise it is the same as this one.