Long story short, amp started pulsing the output loudly while I was listening to a podcast at low volume wired at 4 ohms.
took it to my test bench and found the ka7500 had a bad output, almost all irfp 064n's exploded along with the relative gate resistors, I replaced the ka7500 with an lm494, replaced the 064n's with 064npbf, replaced all gate and pulldown resistors, replaced all resistors in the drive buffer circuit and have changed buffer drivers from c3228/a1275 to bd139's and bd140's.
Upon testing with a variable power supply at 10v everything appears to work fine so far, however with a 4 ohm mid connected for testing there is a faint white noise coming from the output? it's loud enough that you can feel it with your hand on the speaker, could also hear it up to a foot away, The only thing that makes it louder or softer is voltage input, gain doesn't effect it, also
during power down there is also a fast 1 second audible sweep from high to low.
Scoping my variable supply doesn't show any noise, so I doubt it's that, idle current at 10v settles at 2a which seems a little high right? It goes up when I raise voltage.
All transistors input and output did not make any heat on the test bench, the only thing that got a little warm was the power supply transformers.
Anyways how would I go about finding the source of this white noise? It is rather annoying and I don't remember this amp doing that.
I'll try to post an audio file when I get home
took it to my test bench and found the ka7500 had a bad output, almost all irfp 064n's exploded along with the relative gate resistors, I replaced the ka7500 with an lm494, replaced the 064n's with 064npbf, replaced all gate and pulldown resistors, replaced all resistors in the drive buffer circuit and have changed buffer drivers from c3228/a1275 to bd139's and bd140's.
Upon testing with a variable power supply at 10v everything appears to work fine so far, however with a 4 ohm mid connected for testing there is a faint white noise coming from the output? it's loud enough that you can feel it with your hand on the speaker, could also hear it up to a foot away, The only thing that makes it louder or softer is voltage input, gain doesn't effect it, also
during power down there is also a fast 1 second audible sweep from high to low.
Scoping my variable supply doesn't show any noise, so I doubt it's that, idle current at 10v settles at 2a which seems a little high right? It goes up when I raise voltage.
All transistors input and output did not make any heat on the test bench, the only thing that got a little warm was the power supply transformers.
Anyways how would I go about finding the source of this white noise? It is rather annoying and I don't remember this amp doing that.
I'll try to post an audio file when I get home
I had the board out of the case, I wanted to cap voltage and current just in case something else was wrong, I did bring it up to 12v after making sure it was operational.
Do you still have a problem with noise?
Is it a noise that's going to be audible with a subwoofer?
Is it a whistle or is is a noise that covers most of the audio spectrum?
Is it a noise that's going to be audible with a subwoofer?
Is it a whistle or is is a noise that covers most of the audio spectrum?
Oh I am such an idiot, I had my power supply close to the pre-amp section and it was picking up the hum, as soon as I moved it away the noise was completely gone.
I have one more question though, the two 5 watt resistors on the sides of the driver card get hot enough that I can't even touch them, this is just with the amp at idle, is that normal?
