Hi guys, this amp came with distortion problem on one channel. First, the amp produced clean 1khz sine wave test tone, but after a minute the positive wave started to cut. Infact, now it has 0.5V stable dc offset and one output transistor is off and the sine wave is always cutted. So it seems there is an unbalanced stage. All transistor seems to check good. Trying to swap transistor from the working channel doesn't solve the problem. Differential input transistor are also been swapped, but didn't work. Bias resistors check good. Any suggestions?
Thanks
Thanks
If I'm not mistaken, the supply voltage is ok but the Vbe of the TIP142 on the faulty channel is lower that of the TIP142 on the working channel. I'll check them and post here the measure tomorrow. Thank you.
Supply voltage is always stable at about +/-19 volt. Now with 4 ohm load, the upper side of the sine wave is always completely cutted. Without load, the output signal is a dc component (that increase if I increase the signal) and a 0.5 volt peak sawtooth like signal. Vbe of the output transistors (TIP142 and TIP147) is under 100mV. With 4 ohm load connected, there is always 0.5 V DC offset
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