Buzz and Computer Noise When Coax Plugged Into DAC

[BakaOuji]

Noob here, so I apologize in advance for not really knowing what I'm doing.

Backstory: I've been running the Crack 1.1 with Speedball upgrade happily for around three months into HD600s (it really does sound fantastic).  My setup has been optical out of my computer into a Geshelli Labs Enog Pro Dac split into a JVC SP-UX7000 receiver and the Crack. 

Problem: Fast forward three months with no problems and I decide I should hook my Blu-ray player up to the DAC as well.  As soon as I plug it into the DAC via coax, a noticable buzz starts in both channels on the crack, but I do not hear it through my speakers. The buzz changes when I move the mouse on my computer or run programs, so I unplugged the optical from my computer (about 5 feet away from the Crack), but the buzzing and mouse movement changes persisted.  I shut my computer down and the buzzing still didn't go away. It stopped when I unplugged the coaxial cable.

Swapping cables didn't help. Unplugging the receiver didn't help. Re-heating the solder joints around the power and rca jacks didn't help.  I was able to run a DIY O2 Amplifier without hum from the DAC with both coax and optical plugged in, and was able to run the Crack off a different DAC I borrowed from a friend using both coaxial and optical without any buzzing. I also tried a different device with coaxial out instead of the blu-ray player and had the same buzz. All the devices are running off the same surge strip.

I'm not sure what else to try or why this is happening.

Any suggestions?

[Paul Birkeland]

It's very typical in a DAC to have an isolation transformer on the coax input. I can only assume that the DAC you're using doesn't have one and the other DAC that you tried does.  Looking at photos of the DAC you have, I don't see a transformer mounted to the board (it's usually a little box that's about the size of the toslink jack mounted very close to the SPDIF jack).

One thing you can try is to unscrew one of the chassis screws on the BRD player and wrap the end of a wire around it, then tighten.  Touch the other end of that wire to the chassis of the Crack to see if the noise goes away. 

[BakaOuji]

Thanks for the reply. 

Attaching a wire to the BRD player chassis and touching that to the crack chassis didn't stop the buzz.

I confirmed with the company that made the DAC that it does not have an isolation transformer on the coax output. They seemed pretty sure it wasn't needed and think I may have a defective unit.

[fullheadofnothing]

Is the Bluray connected to a video system of some kind? Have you tried isolating/removing those connections?

[BakaOuji]

The Blu-Ray Player is plugged into a TV via HDMI (also on the same surge strip), but I got the same buzz and computer noise when I plugged an audio interface (not connected to anything) in via coax instead.

[fullheadofnothing]

Your video system may have a different ground potential, CATV being especially notorious for this.That's why I asked if you isolated your Bluray from the video system; it might fix your problem.