Occasional hum

[Barry]

This is very similar, if not the actual case - https://www.audiophonics.fr/en/diy-e...l-p-14211.html

looking at the photos, all surfaces appear to be anodised. Thus you will need to re-tap the holes, and re-countersink the holes on the external surfaces. It is almost certain the fixings are metric (M3), so I would replace them with un-anodised steel screws. This should solve the problem

Ideally I would remove the anodising from all mating surfaces, but the above should be sufficient.

Good luck.

[CageyH]

I have just disassembled the case, and removed all anodising from the mating surfaces, and rebuilt the case.
Will it make any difference?

I have my doubts, but it can’t hurt.

[Barry]

I have just disassembled the case, and removed all anodising from the mating surfaces, and rebuilt the case.
Will it make any difference?

I have my doubts, but it can’t hurt.

Let us know the result Kevin.

[CageyH]

All I can tell you is that the resistance between the different parts of the case is now reading 0 ohms, where there was a very slight resistance before.
I really doubt it will make a difference.

[CageyH]

As an update, I believe that the hum problem has been fixed.
I replaced the 7805 voltage regulator with a Texas Instruments LM340T-5, as well as doing everything else listed here, and got quite a while I had had no issue.

I am happy.

[CageyH]

But it came back…
I removed all the internal ferrites. And it was no different.
When doing this, I noticed a whiteish circle directly under one of the capacitors, so as a precautionary measure, I fitted some new Nichicon capacitors. At normal listening levels, I can not hear the hum. I really need to wind the wick up a bit.

I am sure that I have not yet found the root cause, but as long as it does not affect the enjoyment of me listening to music, I can live with it.

[CageyH]

The hum is back.
The AG1500 is back in the system. The hum has gone.

So it is 100% mains based.
I am thinking of building and fitting one of these - https://www.atlhifi.com/shop/assembl...nd-tested-pcb/

Do you think it will work?

[CageyH]

This is the noise in question:
Long version/real time (3 minutes - 33Mb) https://drive.google.com/file/d/14aw...ew?usp=sharing
Condensed version (16 seconds - 3Mb) https://drive.google.com/file/d/11W0...ew?usp=sharing

Any ideas on what this is, or more importantly, what is causing it?

[struth]

access blocked

[CageyH]

Access updated

And thanks.