Cambridge Azur 640A V1 Buzz

Still working on other stuff on this forum. Thought the following would be a no brainer. Sigh... :)

Looking to fix my son's integrated. It buzz's upon start-up then (mostly) goes away after about 30 minutes.

Buzz is there without any signal, only speakers hooked up.

Observed that if you turn the volume up, the buzz disappears around the 9 to 11 o'clock area, then starts again.

I have tried cleaning the volume control pot, and all other pots for good measure to no effect. (MG Chemicals zero residue spray)

I still thinking the volume control, but weird that after warm up the buzz fades.

Any help would be appreciated.

Ed
 
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OK Ed, we are here now. Others may follow now with some better advice once inside the amp. I admit I have never checked inside a Cambridge of this Azur species before but some general principles will apply to all SS amps. I believe this is a conventional class AB type and not the XD type of 740 and 840 models. Anyways, I guess we'll hear from you after the father's day activities.
 
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Assuming you can distinguish between the capacitor types by doing a quick Google search for a wiki with images and explanations, the electrolytic capacitors (usually polarized and marked with +/- or such to ensure you get that part right) are prone to failure and the cheaper the brand/grade, then generally, the shorter the life.....somewhat like batteries.

There is a group of 8 large 2200μF caps that smooth the main power supplies and are located in the centre of the main board. Unless there are indications that the noise only comes when particular inputs or signal sources are used, I'd start with replacing those, test for correct function at least and then work your way through the rest because it's likely none of the electrolytic type are the best quality grade and they're are all going to deteriorate sooner or later. Note, there are some non-polarised (confusingly called bipolar coupling caps) in there too. Replacements for these may be hard to find but don't skimp on them, use something like Nichicon muse (marked ES) if the format is suitable.) The service manual contains a bill of materials for each PCB assembly that you can also use to make up a shopping list.
 
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Yes, these non-polarised electrolytic caps are relatively recent tech. and differ from the standard polarised type by having the oxide layer formed on both foils. It's all about compactness and the high cost and bulk of decent audio film caps. The cheap and cheerful metallized polyester types that once were sprinkled everywhere, just aren't good enough now, unfortunately.
Good luck with the re-cap:up: