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power supply high pitch hum


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I've made a +15-0--15 psu for an audio amp and one channel is reading 15v the other 8v.
I'm getting high pitch hum through one channel and distortion after half volume.I've replaced all the caps, diodes, rectifiers and it's still doing it. Checked the diodes they're okay. Can't fully test the caps with the mm doesn't have cap fuction. checked the transformer output and its okay too. I've had it working fine, but I've done something to it. Checked polarities etc all correct. If I wired it up wrong ie got the +- round the wrong way  to the amp obviously the amp doesn't got but can that damage the caps or rectifiers and cause this sort of problem?
I haven't been able to figure out how to test the regulators with the mm.

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Hi Murrmax,
Welcome to our forum. ;D
Please post the schematic of the power supply so we can see what it is.
Maybe it is overloaded by a blown-up audio power amplifier as its load. Try measuring its voltage output without a load, then test it using resistors as a load.
Maybe it can't supply the high peak current required by an audio power amp. Audio power amps usually don't use regulators to feed them DC power.
It is easy to blow-up a regulator if something was connected the wrong way around. The audio amp might also blow-up.

Also please post the schematic of the audio amplifier. Maybe it has a high current unbalance between its supply polarities.

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The psu is much the same as the kit on this site.
I used a similar kit with supplied components and had it working fine(voltage and current output are fine).
I tested the psu on its own and got the 15 0 8 reading. the psu is seperate to the amp (connected with cable). I think the amps okay, I guess i need to get +15 0 -15 off the rails to tell first without plugging the amp in.
How can I test the regulators using mm.

visually everything looks fine, double checked all my solders, grounds etc.
I have a limited electronics knowledge, bought a mm the other day and figured out reading diodes, transistors, voltage and caps. not too sure about current or regulators.
I'll post a pic when I get home;)
the amps a Gilmore dynalo

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Hi Murrmax,
About the only way to test a regulator is to power it and measure proper DC voltages on its input and output. You could also measure for any AC voltage on its input if its DC is low. Without a load on the regulator, its input AC should be nearly zero volts.

So you have a headphones amp. ;D

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Thanks Audio guru, i'll retest everything tonight. there's gotta be a reason somewhere.. yep it's an excellent headphone amp, probably not a good first project though , the learning curve has been fairly steep.. oh well what better place to start than the deep end...(treading water madly)

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