Hello!
In this topic i will share some tips that could help you solve your problems with K8060 audio amplifier kit.
The strong Hum from the speakers:
- TIP147 and TIP142 are connected in the wrong orientation. Follow the silkscreen on the PCB and connect them the right way.
- One or more transistors are damaged. If you don’t know which transistor is damaged, i suggest replacing all of the transistors with new ones. Otherwise if you replace one that is okay but leave the damaged one, then the damaged transistor can damage the new transistor.
- Check if the white resistors have a resistance of 0,47Ohms. If they have a resistance of 100Ohms or even higher then the resistor is damaged and must be replaced with a new one.
- Don’t set the bias too high. The manual says to set it to around 10mv to15mv.
Distortion at low volume:
- Something is not soldered properly or something has a loose connection. From my experience i had a bad solder joint at one of the TIP147 pins. When i soldered that pin properly, the amplifier worked without any problems.
- You’re using wrong transformer. The manual says that a dual polarity transformer is needed for the amplifier to work correctly. From my experience i tried to connect 30v transformer with only one secondary coil while the amplifier needs a transformer with 2 secondary coils.
- Check if the big capacitors C13 and C12 are soldered properly. For better performance i suggest adding higher capacitance capacitors in parallel to C12 and C13. Remember about capacitor polarity and the voltage rating!!
And now some additional info on how to not blow up your amplifier.
- Don’t set the bias too high. I suggest leaving bias at 10mv because the higher the bias the hotter the transistors will get.
- Don’t connect loads below 4 ohms(such as 2ohm speakers or even electromagnets/coils with low impedance) to the speaker terminals. From my experience i had 1 subwoofer and 2 speakers connected to the same speaker terminals with a total impedance of 2,66 ohms and the amplifier could handle the load but it got pretty hot at higher volumes and required a fan.
- When you first assemble the amplifier, monitor the temperatures and test how hot the amplifier gets and what components get hot. The reason why you should pay attention to the temperature of the components is to avoid overheating. If one transistor fails there is a big chance that the others will fail too and repairing the amplifier can be difficult.
The reason why i made this topic is because i have 4 of these amplifiers. When i got the first one i burned the transistors and resistors, and decided that it would be cheaper to buy another board(it was actually cheaper to replace the transistors and resistors, but at that time i didn’t think about that). Then i purchased another amplifier and it burned because i accidentally shorted the output terminals.
After some time i bought another one and i destroyed because i was experimenting with and electromagnet and a magnet. I was basically trying to play music through the coil and the magnet would vibrate. Unfortunately the amplifier couldn’t handle the low impedance of the electromagnet and the amplifier burned.
Later i participated in a electronics contest and as a prize for 3rd place i won this amplifier. What a coincidence 
I built the amplifier and it was working like it should. I played music with it and everything was good.
Then one day i had an idea to at least repair one of the amplifiers so that i can have 1 for the subwoofer and the other one to the speakers.
I managed to repair it and made it so that Right audio channel is connected to subwoofer and the Left audio channel is connected to the speakers.
Recently the amplifier was plugged in and i didn’t play any music through it and the subwoofer part of the amplifier caught fire. I quickly noticed the fire because i heard the loud hum from the subwoofer. Also the speaker amplifier had short across TIP147 collector and emitter.
Nevertheless i fixed both amplifiers by replacing all transistors and the burned resistors and now they’re working fine.
These amplifiers have a very good sound quality but a simple mistake can ruin/damage the amplifier so be extra careful when using this amplifier.
I hope i helped to fix your problems with K8060 amplifier! 
Have a nice day!
-Salins
