Try a 0.1 uF film cap of appropriate voltage rating directly across the power supply connections for the power transistors.
Consider beefing up the electrolytic bypass capacitors.
Bypass is your biggest problem.
Look at any commercial build. The power electrolytic capacitors are always together. You should do this too.
Try the film cap too.
I added 0.1 uF film cap, but the high distorted sound still exist.
Yeah, it's already connected with two 4700uF cap on +/- rails in the way that told.
Your physical layout is just all kinds of wrong and introduces inductance in all the wrong places! Even if the amplifier worked OK addressing these issues will clean up the sound. I do prototypes and sometimes they're not pretty but I still have to pay attention to stray inductance in a feedback circuit.
Having those traces non-soldered on top that appear they should be connecting components, but really not, is adding some capacitance and inductive noise plus concerning questions why they exist.
why all the "extra traces" on top?
Before you go any further you have to solder ALL parts on BOTH sides or the circuit will not work.
You are right guys I'll fix it before anything else. When I was making this circuit I didn't notice that I mirrored the layout twice. so I printed on another side.
Oh--and a thought that crosses my mind before i think of building anything audio (or a lot of circuit in general), is that i absolutely need some kind of oscilloscope to figure things out.
We should have everything prescribed as being on a heat sink.
Yes, I agree. But right now the price of a appropriate oscilloscope is a little high for me. I'll buy it later.
That's right, I'll take care of that. It was mounted to a heat sink but I had to use it for another STk amplifier.
You appear to have made a double sided pcb with the same print on both top and bottom - am I correct?
Yes, It happened because of a mistake when printing. So I printed another one at the second side. but I was wrong to didn't clean first side.
mshey, i was was only hinting at what chalky has stated to see if we would all see it the same including you.
this board needs to be redeveloped with traces on one side only.
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Yes Sure Anducer, I'll attach better picture. Do you mean that I take selfie with it?

I'll do it ASAP and report the result.
Right now I changed the heat sink temporary with this small one.
Thank you all for answering and helping.
