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Listener666
16-05-2010, 21:50
help... I have a buzz!

I use a yamaha MXD-1 digital pwr amp and a Copland pre.

The Copland only has RCA O/Ps the Yamaha has RCA or XLR

I am getting a buzz (prob earth although its a bit high pitched for mains hum) through the speakers when the DAC is connected (either fixed or variable) and either through the pre or directly into the power.

I can get rid of the buzz by connecting the dac to the pre and using an XLR
cable to the power and adaptors from the RCA O/P's of the pre....not ideal!
...and I like it connected directly....(i have a little project in mind to run my turntable into a ADC:stalks:)

I have swapped all the mains cables about and tried different blocks etc. I think the power amp is very sensitive to mains noise as the mains lead has 3 big ferrite thingys on ( i tried two other leads).......or.......

could it be that noise from the switched mode dac power supply is being picked up by the power amp?

any ideas?

Stratmangler
16-05-2010, 22:53
You've got ground loop issues by the sound of it.
Try running a wire from the case of the DAC to the case of the amplifier.
It may cure the problem.

Notice the use of the word "may" - curing ground loops is not an exact science in itself.

Fingers crossed that this works;)

Rare Bird
16-05-2010, 23:14
Can't you just strip the lot down the barebone essentials & build up a bit at a time.. Check you not using 3 core mains cables on things that only need two.

Listener666
17-05-2010, 16:27
Can't you just strip the lot down the barebone essentials & build up a bit at a time.. Check you not using 3 core mains cables on things that only need two.

Yep...I have done the strip down bit........everything is fine until the 7520 dac is connected.....then buzzzzzzz!

I will try an earth wire from the case...........

I didnt think of the three wire mains when no earth is needed thing....mmmm Just remembered the buzz got worse when i swapped the digital power amp lead for a different one....which has three wires (the amp has 2)......I will try the other leads.......thanks

What puzzles me is why there is no buzz when using the XLR connectors....................Power amp earthing through the pre amp via the XLR perhaps maybe?????