ghost power supply buzz?

[Tom_Teddy]

Hey everybody!
I have The same problem with a buzzing device.
So first of all thanks everybody for all the information I got from here. Since I am in Europe I got myself some bridge rectifiers from Conrad electronics. I am a bit unsure if they are the right ones so it would be cool if you guys could give me a go for putting them in.
Thanks 1 million times!

Thomas

[Scodiddly]

Those should work.

[Tom_Teddy]

Cheers mate.

[The Scum]

Does this fix help other devices experiencing the same symptoms?

I've got an old Carver power amp with a humming transformer that I've been living with for far too long, and if a $5 part fixes it, that would be great.

[Tom_Teddy]

That goes to far me.
But I think I would open it up and see what’s inside. If you find bridge rectifiers which are easy to change do it.
I changed two of them a minute ago and now and I can’t hear anything. It worked perfect for me.
My problem is that the Fans don’t start to turn and it gets hot as hell. Even though I changed the fan to the one someone mentioned earlier,..
Someone has an idea?

Cheers

[Scodiddly]

Does this fix help other devices experiencing the same symptoms?

I've got an old Carver power amp with a humming transformer that I've been living with for far too long, and if a $5 part fixes it, that would be great.

I've really only ever run across this issue (and fix) in those Soundcraft power supplies, the CPS-275 and probably some similars. But I don't see why it couldn't work in some other gear.

[jimjazzdad]

Wait. I have a Soundcraft CPS 150. You guys are saying it is the bridge rectifiers causing the buzzing noise, not poor construction of the transformer? I had always assumed that it was loose laminations or windings on the transformer that cause the 60 cycle hum. I have attenuated the buzz to a reasonable level using some special, multi-layer, noise damping foam, but I would love to change out a BR and have it stop. I have already changed BR1 & BR2, as advised in the Soundcraft Service Bulletin as well as R32 and new caps at C1 & C21 (to reduce sag on the 17V rails). It still buzzes.

[Scodiddly]

The transformer buzzes when there is a lot of current through it. Leaky bridge rectifiers increase the current beyond what the mixer draws. But if you're running your PSU hot to begin with then there may be nothing you can do. Other than getting a PSU with a higher output current.

[jimjazzdad]

Got it.

Its the 16 channel Spirit Studio and I think the CPS 150 is spec'ed for up to 24 channels in this instance (I believe the 32 channel version comes with the CPS 275). Anyway, the Soundcraft PSU are notoriously unreliable according to the interweb - that's why I upgraded some components, as recommended by the manufacturer. I suspect the transformer is maybe a bit undersized and is stressed accordingly...good old British 'lecky' stuff