NigelTufnel

Looking around some more I have discovered that there ARE in fact isolation transformers on the galvanic (metalic) inputs. That kind of sucks because that is harder to solve via an external fix. Furthermore, it doesn't actually matter which connection I used. Bad test on my part. So long as the DAC is locked onto an incoming signal, you'll get this pulse on the output, regardless of whether you use RCA or Optical S/PDIF. I had the wrong input selected when I tried optical, that's why I thought it was possibly a ground loop issue. Maybe Telig is secretly not even listening to DAC's, but just using a scope? That would explain his conclusions.

Here is a pic of what I'm talking about. There is the usual power supply related hum but those alternating up and down spikes are only when using coax with Logitech Squeezebox. I'll now have to go see what happens when hooking up USB.

Forgot to also mention, I'm using an after market, linear supply from TeraDAC for the Squeezebox.

I know this is a very old thread, but I just found something relevant. I've been doing some poking around at the circuitry and outputs of my DAC 8, maybe considering a capacitor modification. Anyway, before I did anything I looked at the output and discovered a lot of noise on the balanced outputs. Around 125uV happening at odd intervals. To make the long story short the issue was noise coming from my Squeezebox through the coaxial S/PDIF connection. Switching to optical removed the noise entirely. I'm not sure what's going on, but I suspect some of this could have been prevented if ARC had used transformer coupled inputs, which they seem to have avoided. Note that the Logitech was plugged into the same strip for all these tests. If it was a power supply noise issue, it would still be there after going to optical. It is also possible, if this is a ground loop issue, that a lot of expensive alternatives may have prevented this problem, such as balanced output isolators, lifting the ground from the DAC8 (NEVER do that, it's how fires get started and insurance refuses to pay), or isolating the power via a power transformer (may not work for complicated reasons, but the founder of Jensen wrote a paper explaining why). If you want to do this test yourself, just hook an oscilloscope to the outputs without a signal, and look at the muted vs. non muted output. In my case the unmuted signal showed clear spikes happening every few microseconds.