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SS Amp needs repair


OLLY

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I have a diy amp that a mate built me just before he passed away and I cannot find anyone who will attempt to find  what sounds like an earthing problem. They take one look inside the chassis and walk away. Does anyone in Perth (South Of River) know a retired tech who would be interested in helping out. I have a feeling that the problem started when he tried to get the LED display working evenly.  Any help appreciated

Cliff Amp 1.JPG

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Hi,

That is because there's no diagram for it.

Ask the widow for the technical notes left behind and maybe you'll have better luck.

Is the buzz only in one channel or both?

Disconnect speakers or move balance in the preamp to check for this.

I can see heat discolouration on the right side (left channel), near the aluminium heatsink.

Cheers 

Roman

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Only one channel has a problem. No circuit diagram as he built everything that way.  Used old boards he had laying around and that is why you see the heat marks in the left channel.  Any good tech will be able to trace back to the source the way Cliff did when fixing gear.  To watch him was something. Pity he tried to improve something that really did not need fixing when he was in the condition he was in was asking for trouble, hands shaking all over the place, not good.

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I could be wrong but the main amp modules look like an old Playmaster Designed by the boys from ETI.  The pcb layout looks so familiar.  If it is, the cuicuit diagram will be published in one of the old ETI editions.  That smaller pcbs I'm not familiar with, the one with all those yellow wires are obviously introduced for either a display  or control for the front panel, no idea what the bread board is! 

Any buzz via one channel only then the best you can do is look for bad solder joints on the module that's the issue.  I can see on the right side of that module that some of the resistors have over heated and may have been replaced.

Edited by Addicted to music
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3 minutes ago, Addicted to music said:

I could be wrong but the main amp modules look like an old Playmaster Designed by the boys from ETI.  The pcb layout looks so familiar.  If it is, the cuicuit diagram will be published in one of the old ETI editions.  That smaller pcbs I'm not familiar with, the one with all those yellow wires are obviously introduced for either a display  or control for the front panel, no idea what the bread board is! 

Any buzz via one channel only then the best you can do is look for bad solder joints on the module that's the issue.  I can see on the right side of that module that some of the resistors have over heated and may have been replaced.

I agree the amplifier boards look like a Playmaster, it is not the Electronics Australia "EA 89 ma 11" board.

It does use the same Hitachi mosfets as the "89" board.

The boards (3?) with the yellow leads is possibly a VU meter type arrangement.

The vero board near the power transformers may be a power up delay circuit.

The vero board near the front right of the photo may be a phono stage?

Your local library may be an option for old EA/ETI magazines that would have circuits and build articles.

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When you say an earthing problem can I assume that it is a humming sound . 

Is the hum coming from the l/h channel (the one with the burnt board ) and does it vary with volume level .The amplifier modules could be a ETI project .

It looks like it was a dual mono design and he added an led display and some sort of preamp ( top rhs board ) and a volume control . He built a new power supply to power the led display and preamp? .The small transformer between the two large ones  is sitting right on top of the inputs  ( not good ) .There may be an earth loop in his wiring or a faulty o/p channel .Don't think you could get parts for this if they are needed .

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If you are not in a hurry you can drop it off at my place.

I am a hobbyist and like a challenge.

No guessing from me what the problem might be. To many possibilities.

Free of charge. Just pay for parts if needed.

Stephan

 

Edited by Ihearmusic
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