...about the 25W MOSFET(or HEXFET) amp...again...

[xtp]

If I supply it with +-12V, I reduce the current of the 2nd current generator (Q5&Q6) ???, I replace the BD139-BD140 pair (Q6&Q7) with small power transistors and I replace Q8&Q9 with normal transistors what else should I change?
More answers please...

 

[audioguru2]

Hi Sasi,
1) I would remove R14, R15 and R18.
2) The driver transistor and its current source are designed to provide a very small current for the Mosfets' gates but not enough current to drive bipolar output transistors. Maybe the output transistors should be darlingtons to operate with the low driver current.
3) With a lower supply voltage, the current sources wouldn't provide enough current, so the values of R4 and R9 would need to be reduced.
4) Of course with bipolar or darlington transistors the amp will oscillate since they are much slower than the original Mosfets. The values of C9 and R8 would need to be changed accordingly.  ;D

 

[audioguru2]

Hi again Sasi,
I nearly forgot. With a total of 66V for a supply, bipolar or darlington output transistors wouldn't have the huge voltage loss of the Mosfet-followers, so the output power would be much more than only 25W and the output transistors and power supply would fail due to too much current. 

I would just use an audio amp IC for power of 50W or less. All expensive parts are included in the inexpensive IC and no tweaking is necessary.  ;D

 

[audioguru2]

Hi Sasi,
You have a good idea to use a coil at the output to isolate capacitive loads.
R14 and R15 should be deleted since they cause severe crossover distortion.