Having recently changed my amplifiers from vintage Quad to a vintage Leak Stereo 20 with a passive preamp, I’ve been plagued by ground loop issues. I’ve managed to get silent vinyl playback by using a phono stage without attaching the turntable ground wire to it. However digital is proving very difficult to solve.
I have a Nucleus and had until recently been using a Chromcast via optical output into a Quad 99 CDP-2 to play Roon. But I sold that CD player as I wanted something more modern to play my DSD files. I had a Pro-Ject Stream Box S2 Ultra and DAC Box S2+ combo (which connect to each other via USB) lying around so decided to try them out, which resulted in a ground loop. I tried going directly from Nucleus to DAC Box S2+ and that too made a ground loop. I then tried an old Arcam airDAC (with Chromecast via optical) and that made a ground loop too. Two days ago I received an iFi Defender+ USB isolator as I thought the USB ground was causing the problem, but it did nothing at all when used between the Pro-Jects or the Nucleus and DAC.
One thing I have noticed is that the hum seems to be present when I’m using devices with separate wallwart PSUs (the exception being the Chromecast when used via its line out into my preamp, which is quiet). When I’ve used devices with internal linear PSUs like my Quad CDP or old Sony Minidisc there is no hum. Does anyone have advice, should I just buy random digital sources with fingers crossed? It’s giving me a headache these last few weeks.
EDIT: bit rate
If you’re really having a ground loop and don’t plan to go beyond 192kHz/24bit, there’s a rather cheap true USB isolator that HiFi measurement blogger Archimago tested recently - and more to be found on the net.
If you’re planning on higher sampling rates than 192kHz/24bit, AFAIK there’s only one company selling a working solution these days: Intona
The linked unit will suffice, but they also carry units with even higher isolation voltage rating and/or USB3.
We’re not talking snake oil products here, these are truly isolating USB power and data lines and thus eliminate ground loops.
If one of these devices doesn’t fix your ground loop, then it wasn’t one to begin with - in that case, please refrain from posting negative comments about the device in question!
Hi Woo, I looked at the devices you are using and it seems that none of the analog outputs are balanced. Can you confirm? Using balanced analog connections is one of the most effective ways to get rid of ground loops. I would start by trying a DAC with balanced outputs. If the preamp/amp does not have balanced inputs, you can use XLR-to-RCA cables.
After some thinking and testing today, I’ve established that there isn’t a ground loop as there’s only one path to earth - via my Leak power amp - so there can’t be a ground loop. The problem seems to be noise pickup. Digital sources like my old Quad CDP and my old active preamp both with linear power supplies seem to have filtered it out in the past, but now I’m using a passive preamp the noise created by the Pro-Ject and Nucleus’s SMPSs are making too much noise and the Leak - being so sensitive - is amplifying it. Seems I need to choose a digital source with a proper well-designed PSU rather than the inexpensive and basic wallwarts.
The power amp, a Leak Stereo 20 is from 1965 and uses RCA inputs, as does the Khozmo passive and Pro-Ject DAC Box S2+.
As mentioned above, I’ve established that it’s not a ground loop this time (although I had two of those recently with the Leak when changing equipment in the system). It seems some digital sources I have are able to filter out the noise better than others, so I just need to test any new sources in my system first.