Through the use of powerful constituents (Darlington) transistor T4, T5, final stage managed to produce a sufficiently powerful amplifier of the five transistors, and three of them are shallow.
The output stage operates in B, the displacement at the bases of transistors is defined by two diodes D1, D2, which excludes the building process. The input stage, the differential pair supports a “zero” level “to break” and closes the negative feedback circuit of AC.
When you build should pay special attention to placement of elements on the board and the amplifier power supply to eliminate self-excitation of the amplifier, which can damage the output transistors connected to an amplifier and acoustic systems.
Note : Separate and adequate heatsink is needed to reduce heat in the transistor TIP142
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I built the Amplifier but it sounds like there is a leaking capacitor, Audio is very low and slightly distorted. Initially I thought that one of the Darlingtons was gone but after testing them they are ok. I then discovered that my power supply voltage was at 49 - 0 - 49. I am still working on it, any helpful hints are much appreciated
I took a look at the schematic and know what the problem is. It is called crossover distortion. This results because the two diode drop does not provide enough voltage to bias the output transistors when they are idling at zero volts. The output transistors are Darlington types that have twice the base-emitter voltage drop as regular transistors. To correct this problem, you need to add one more diode and a small resistor, 22 ohm, in series with the two diodes between the bases of the two output transistors. Simulations indicate that this should eliminate the crossover distortion. The T4 and T5 emitter resistors should have 6 to 8 mV across them with no signal input. This means about 20 mA is flowing through the output transistors at idle, which eliminates the crossover distortion. Hope this helps. Good luck.
i use same circuit with a power supply of 25v positive negative and find it working perfectly