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The voltage on U2 output raises and falls like output voltage if I turn current adjustment pot. The lowest voltage on outpu of U2 is 17V, the highest is 35V (I was meassuring pins 6 and 4??)..

No, that's just on my schematic becouse of Kicad (doesn't have BZX85), but actually, I used BZX85C. What could be the reason also? Why is voltage changing when I turn current adjustment pot? I double checked PCB and it's completely short connection free. It's soldered good and everything is checked with Kicad, so all connections are fine. There must be something with components, or my transformer is the problem (24V/250VA).

This is exactly the one I built. So, audioguru, can you answer me, what can I do about my issues to solve them. I also noticed, that PSU has no power. If I connect a load on it, the voltage drops unnormaly.

I think, there is no problem with this schematic and PCB.. @audioguru, C8 isn't shorted.. sch.pdf pcb.pdf

I've noticed something new: If I have pot for voltage adjustment set to maximum value and I am changing current limit pot value from minimum to maximum, something strange happens. At it's minimum, output voltage is 40.5V. Then I am slowly raising it. The output voltage stays 40.5V for about 1/4 of a circle, then it starts to fall to 30V, and then again raising to 35V, and than finally falls to 24V at maximum value of pot for current adjustment. I don't understand. Is my pot broken? PS.: And I am using 24V/250VA transformer.

You've disunderstood me. I am also adjusting voltage with P1 and current with P2, but with RV2 I can set the maximum output voltage. I used schematic that you posted it one page back. PS.: I still don't know, why LED is always on. What is the reason, what can I do?

The newest version with mc34071 opamps.

I built it (3A version) and I have a few issues: - current limiting LED is always on (if I turn current pot to max value it even lights more) - I just can adjust minimum voltage to 50mV with voltage trimmer - what can I adjust with other two trimmers? However, PSU woks fine, the maximum output voltage with no load is 40V.

Nice PCB you have there. But mine is made just for 3A version, so I think the thickness of output tracks is good. Here is final version: pcb.pdf

Here it is: pcb.pdf

This is becouse of .pdf file. When I print it it's ok. I am working on strenghtening pads.

If you have Kicad, you can try mod my verison to 5A. I can try it too, but not this week.

Ok, I re-drawn my PCB, so it's jumper-free. I also strengthened all tracks, so this is my final version I guess. I will try it once this week and I will report. dokumentacija.zip

I am planning to use 24V/250VA transformer for this project, since this is the only one I have now. Is this ok? What is the difference if I use 10000uF instead of 12000uF for C1 (for 3A design)? Has anyone tryed to draw single-sided PCB for new 3A project? PS: I drew PCB in Ki-cad. Can someone, please take a look at it and tell me if it's good? If it is, then others might use it too. dokumentacija.zip

I am working on this. I completed .sch file in eagle and now I am working on PCB project. When I am finished, I will publish it here.

Why it worked then? I mean with LC filter. It reduced oscilating and noice brum..What is wrong with that connection?

I connected it like this:

I repaired this trace. I soldered 1mm wire instead of pcb trace on it..I will get new parts tommorow maybe. Or else latest in monday. I will report. But I am also afraid, that when I will play on full volume for too long, something will die..Even heatsink won't help. Oh, and about oscilations. Would it be good idea to connect 520pF capacitors between base and collector of Q5 and Q6?

Just to report, I made an LC filter to reduce oscilating and brum..I connected it in series with C13 and to power amplifier...It works great, but I burned everything ;D I turned Volume potentiometer to full and played for 2 minutes really hard, when suddenly everything shuted. I checked PCB and saw broken connection between Q6 Collector and ground..(it was verry tinny connection)..I repair it and replace C6. When I turned circuit on, it started to smoke..As I assume, Q4, Q5 and Q6 are dead. One of them was dead before (Q4 or Q5), so it started to smoke...I am wondering, if I am using to small cooling rib or not too good contact from collectors to cooling rib. I am waiting for new parts. I will replace every transistor and check them all to prevent puting in a faulty component. I will report and I just wanted to say, that LC filter solve the problem of oscilating in huge rating..I will report

But in this contribution it says, not to connect them together...Can you draw me, how to connect grounds with use of star grounding..I would very appreciate that. Thank you

Yes I know what star grounding do, but I don't know if I can use it with my PCB. I should separate grounds of preamplifier from grounds of power amplifier, am I right? In that case, I must make new PCB.

Can you tell me something..How can I use star grounding with my PCB. I think, i can't, becouse I used a copper ground...I can't wire every ground to the star connection with different wire. I am confused now.

Yes I will shield everything when I make case from aluminium and put everything in. I will then make grounding on the case and I will insulate case to prevent it to electricute me. So you thing shielding will make this oscilating go?

I disconected preamplifier and power amplifier still oscilated. I connected 1k resistor in series with C9, like you said and oscilation stoped. I hear very quiet hum in speaker, with volume potentiometer set to 0. I must try connect preamplifier back and try put some signal on. I will report. EDIT: Now it oscilates when I turn Volume potentiometer to maximum... ???

i did that. I connected 0V rail to radiator. What is screened cabe? In Slovenian forum, I got advice, to remove C10, becouse this capacitor causes many unwanted effects. It drives signal from power amplifier back to preamp and cause oscilating. Amplification without this capacitor is much lower, but reduces oscilating. What about that?