Playmaster 300W amp humming and thumping - Page 2 - diyAudio
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Old 4th August 2004, 10:37 AM   #11
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Location: Newcastle, Australia
The May issue only has the PCB overlays and construction - no circuits. I could deduce the muting transistor on the preamp overlay, with reference to it in the text, but don't have any circuit details of how it is controlled. Still think speaker switching is a better arrangement.

If you are going to move the transformer closer to the front of the box, you might also consider moving the bridge to a position directly between the transformer and filter caps to reduce cable lengths.

Cheers
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Old 4th August 2004, 10:44 AM   #12
ccoutts is offline ccoutts  New Zealand
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Thanks. I've found both editions at a library, so will get those tomorrow. Librarys are still useful! ;-)

Yeah, will shorten the cables when I reassemble it.

Tried shorting the ends of an RCA lead connected to the input while it was turned off and thumping (to try to simulate the effect of the input muting circuit). It changed the rate of the thumping, and its volume, but didn't remove it completely. Weird.

What is "speaker switching"? Do you mean having a relay disconnecting the speaker after power off?
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Old 4th August 2004, 12:58 PM   #13
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Quote:
Originally posted by ccoutts
What is "speaker switching"? Do you mean having a relay disconnecting the speaker after power off?
Yes. There have been a number of designs in EA, ETI and Silicon Chip incorporating DC protection as well, and these used to be available as kits from most suppliers but they don't seem to carry them now. Altronics has a couple of kits but not sure of the details of them.

Another thought on the thumping might be to temporarily remove the input RCA from the case and let it dangle in another position and try it to see if close proximty to speaker terminals has anything to do with the problem.

Cheers
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