Strange 300b Push Pull Noise

[david]

Hi,
My WAD 300b push pull clone has developed a strange noise. I would describe it as a fairly regular click, at 1 second intervals. And no it doesn't chime once an hour

It reminds me of the static noise some of us got before we earthed the metal covers of mains txs on Kat 6550s and 34s. But it's not that as earthing the mains tx or metal caps or output txs makes no difference. It occurs on both channels, independent of volume of course as it's a power amp. I might have disturbed something when I improved my speaker wiring last week but I thought it was OK after that.

It will be a few days before I can lift the bonnet, so thought I'd get some other fine, analytical minds working on the problem in case anyone has any bright ideas!
Thanks

[Richard]

Hi David, is it through the speakers or mechanical? If through the speakers it sounds like motorboating, slow phut phut sound. Is your circuit standard spec and are you using feedback?

[bearded fiddler]

Hi David,

I had the same problem when my amp was settling in. It was a sparking noise, but without actual sparks being seen. It disappeared around the time I removed battery bias, but that could have been a coincidence of course.

Jan

[John Caswell]

Hi David,
Following on from Richard's comment, if you are not using feed back is the L/S secondary of the optx earthed? Apart from that it does sound like static discharge.

John

[david]

Hi,
It comes out through the speakers. The circuit is absolutely standard, apart from increased capacitors on the Schottky high voltage diodes, so the speaker secondary negative is earthed.

I'm sure it's not motorboating. It really does sound too regular /more like static. One interesting thing is that it stops instantly when you turn the power switch off, it doesn't fade away.

Up until yesterday evening the amp was very silent over 20-30 hours of use, with very low hum /hiss, and it was not picking up any extraneous electrical noises either. The sound as Jan says is like sparking, and very similar to the self curing noise of polyprops, but pretty regular.
David

[david]

Ok problem solved! It's the noise you get when you don't solder one end of a high voltage Schottky into the psu! I missed it in bad light and it's a little tight in there. So back to audio bliss!