I recently put together a small amp from my so called junk box of parts and the amp is up and running with no DC offset, overheating or other problems except bad distortion.. I used an unregulated power supply board fed with 24 volts on both rails but after measuring the voltages on the Vcc and Vee pins of both boards it is higher then the recommended 35 volts max. My readings show 38.7 on one channel and 38.9 on the other. This is a bit over the maximum suggested by the board manufacturer and possibly the issue for the distortion.. Is there a way to reduce the output safely and reliably down to say 30 volts or even 25 without too much trouble.?. I could change the transformer to a lower voltage one but this is an added expense. I also measured the ac coming of the transformer and it is higher then the 48 volts CT then it states.. Any suggestions would be welcome.. I did read somewhere that you can use a zener diode to reduce the output but this does bot sound reliable or safe in my view Thanks for reading Cheers Wayne

 

Do you have the schematics of your power supply and power amplifier modules?

 

Do you have the schematics of your power supply and power amplifier modules?

Thanks for the reply.. I will try and get them for you. Nothing came with the boards.. Might have to go back to supplier in China.
Give me a little time on this.. Thanks again.. Cheers Wayne

 

Do you have the schematics of your power supply and power amplifier modules?

Contacted seller in China for schematic of modules.. I do not have a schematic for the power supply board. The supply is a simple split one powered by a transformer with a 24-0-24 ct secondary and fed to a bridge rectifier with two caps in each line of 4700 mfd .. My calculations indicate that it should generate about 33.6 volts DC but it is coming out much higher due to higher AC input at transformer end.. I will try another transformer if I can find one just to confirm higher then required voltage is the cause.. Thanks for your reply..I will contact you when I get the schematic.. Wayne

 

You can trace the circuit and draw the schematic.

 

You can trace the circuit and draw the schematic.

Thanks Joe.. I was able to substitute a transformer with a lower secondary voltage and the modules are now getting 26 volts and the distortion is gone.. Thanks for your input on this.. Seller in China was not able to supply schematics... Thanks again..Wayne