So, as we know (and we discussed the basic Goodies class in the push-pull amplifiers are very good efficiency. However, due to the lack of initial bias current to the output transistors have a very high nonlinear (transitional) distortion. So listen to these amplifiers is not possible. However - if you can't, but really want to, you can.
Your attention is invited to the amplifier In class with the following characteristics:
The voltage, V +/-24
Input resistance, 10 kω
Nominal (maximum) power output, W: 40(60)
The frequency range 20 Hz...20000
Total harmonic distortion, % 0,08
Look at the diagram:
Extreme reduction of nonlinear distortion was achieved by controlling the transistors of the output stage, not voltage, and current. That is, the transistors VT1 and VT2 are the current sources for VT3 and VT4.
Without going into deep details, let me just say that this amplifier was assembled and worked without any setup for a very long time, until some irresponsible citizens did not pleskanul of beer on the radiators of the output transistors. It is why it is not liked.
However, the method of tuning the amplifier described by the author of the scheme.
For starters, without load, the selection of resistors R7 and R8 is established on the bases of the transistors VT1 and VT2 voltage equal to 0.4 to 0.5 volt. Then, the resistor R5 is set to zero, the voltage at the amplifier output. Then, a load is connected and listen, what of all this happened.
The amplifier is not critical to the selection of elements and does not require the selection transistors. Operational amplifier CDA can be replaced by CAD or CAD. The output stage transistors are mounted on the radiator area of not less than 600 sq cm And the transistors VT1 and VT2 to the individual radiators 60 sq cm