Problem hum / buzz from Power Supply

[Spur07]

Hi

I recently acquired a home brew Dac from a Hi-fi enthusiast in Italy. It sounds great but the PSU (housed in separate box) has a slight hum / buzz which is amplified through the speakers.

The buzz is apparent when you take the lid off but I can't identify exactly where its coming from. The power lead is 2 pin Schuko - the 13 amp 2 pin adapter I'm using is earthed. I'm guessing something in the circuit isn't quite performing as it should.

I'll try new fuses (when they arrive).

Any suggestions as to how to identify the offender? I'm not qualified to go messing around with power supplies. Does anyone know someone in the London / Surrey area, or further afar, who could take a look for me if needed? Any ideas from you good folk much appreciated. Renumeration provided and a chance to play about with a cool Dac.

https://s2.gifyu.com/images/20190324_081201.jpg

[struth]

might not be 240v tx's and they are humming

[Barry]

I was going to suggest that you may have some DC on your mains supply, which often can cause toroidal transformers to buzz. However the size of the transformers in your power supply look to be too small for that to be the cause.

Is the hum/buzz mechanical, or is it electrical (i.e. can be heard through the speakers, but will disappear when the amplifier is switched off)?

[Jazid]

Send it to Juancho or toprepairman, either will sort it out no worries.
My money's on an earth loop issue but could be overvoltage Trafos just as easily.
What kind of DAC is it, valve output perchance?

Sent from my BLA-L09 using Tapatalk

[Spur07]

might not be 240v tx's and they are humming

thanks Grant

[Spur07]

I was going to suggest that you may have some DC on your mains supply, which often can cause toroidal transformers to buzz. However the size of the transformers in your power supply look to be too small for that to be the cause.

Is the hum/buzz mechanical, or is it electrical (i.e. can be heard through the speakers, but will disappear when the amplifier is switched off)?

I'm no expert but I'm guessing it must be electrical Barry - if I switch the Dac off the buzz disappears. My Quad power amps are extremely quiet with minimal white noise. I'm pretty sure the buzz I can hear from the power supply is the same I here from the speakers, if that's possible.

Last night I moved the earth wire to a lone location on the chassis but no change unfortunately.

Someone else on DIY audio suggested I rewired the Schuko to standard 3 pin plug.

[Spur07]

Send it to Juancho or toprepairman, either will sort it out no worries.
My money's on an earth loop issue but could be overvoltage Trafos just as easily.
What kind of DAC is it, valve output perchance?

Sent from my BLA-L09 using Tapatalk

Thanks for the heads up James, that's really helpful.

Yeah, its valve output from a Buffalo III board. Ill post a photo of the dac when I get a chance.

[Jazid]

Buffalo 3 has excellent CMRR so it'll be a ground loop or crap on the HT at a guess. Did you give David a bell?

Sent from my BLA-L09 using Tapatalk

[Barry]

I'm no expert but I'm guessing it must be electrical Barry - if I switch the Dac off the buzz disappears. My Quad power amps are extremely quiet with minimal white noise. I'm pretty sure the buzz I can hear from the power supply is the same I here from the speakers, if that's possible.

Last night I moved the earth wire to a lone location on the chassis but no change unfortunately.

Someone else on DIY audio suggested I rewired the Schuko to standard 3 pin plug.

What I would do is to only power up the DAC, leaving everything else switched off. Now if you can hear hum/buzz when listening near the DAC, the problem is mechanical, and can most likely be cured by tightening the fixings of the toroidal transformers.