[dean0]

Just put together my second o25 PSU build for 5v output. The PSU delivers 5v (4.94v to be exact) but there is a loud buzz/hum noise when connected to my y2 DAC. I'm all out of ideas, any advice would be very helpful.
Thanks
dean0 
 
 
 

 

[FallenAngel]

Ground loop?

 

[digger945]

WHat kind of measurement do you get when you set your dmm to AC volts?
 
Also, what kind of dmm are you using?
 
Is it possible for you to share a picture of your project?

 

[qusp]

sure sounds like a ground loop, but yeah without pics its hard

 

[dean0]

 

[Yoga Flame]

Any change if you disconnect the sigma board from AC ground?
 

 

[dean0]

nope I tried that already, all out of ideas, could a faulty component cause this kind of problem?

 

[sandbasser]

Have you thought about posting on AMB's forum???

 

[MisterX]

Get rid of the black wire that is connecting the "G" pad on the Sigma 25 to the earth ground.

 

[dean0]

Tried disconnecting the ground pad wire and reheated all joints, still no luck. I took some more measurements... 5v when I set the DMM to V- 20 but I get 9v when set at V~200 , any ideas?

 

[KT88]

That's why I don't like cheap DMM's (even though I've had the same issue with a bench top 5.5digits Agilent).
 
Try measuring the DC voltage at the input of the regulator under the same conditions (same load, etc). Perhaps the input is too low under load and the regulator can't keep regulating.