I have built two K8060 amplifiers, and at first they worked fine, but after a while one of them emitted smoke from R4 and stopped working. Only hum in that channel. I tried to replace R4 (330 Ohhm), but the same thing happened. What is wrong?
Most likely, one or both power transistors have blown.
Make sure input voltage is within specs.
Make sure unit gets adaquate cooling.
Make sure quiescent current is correct.
In this case, we’d recommend to replace all transistors, not just the power transistors.
I have come to the same conclusion, after stuying the schematic.
If the bias current was too high, the Darlington couples could have blown.
This would put 66 V across R4 (680 Ohm),
which would cause P=U^2/R=66^2/680=6.4 W in R4,
which of course would burn it to a crisp (it’s only a 0.25 W resistor).
I replaced all the transistors, and two resistors, R4 and R16. The amplifier works, but has distortion. What could be the problem?
I should add that the bias can not be set below 38 mV.
Did you replace the power transistors with the same brand?
This can be critical.
Sorry, this is difficult to troubleshoot from a distance.
Maybe you could compare voltages at certain points with the voltages you measure on the amp that is working correctly
Did you replace the power transistors with the same brand?
Yes, TIP142/147.
I suspect that the PCB was damaged when I replaced R4. A tentative solution would be to solder some cables instead. Have not tried that yet.
This kit is more difficult than I had expected. The PCB is extremely sensitive to a tin sucker, the printed circuit will easily come loose. You had better do it right from the beginning! At least this time nothing burned.
That did not work. I got a new K8060 kit, and built it from scratch, now it’s working flawlessly, both channels.