NDX and n-Vi : Adventures in grounding.

I thought i'd share some thoughts on grounding after my experiences over the weekend.

I have two Naim source components plugged into the XS. My previous Weiss and Lavry DAC's connected mains earth to signal ground in the same way as a Naim CD player does so my system always followed the recommended Naim approach with one source component making the 'ground'. The Linn ADS had no issues either. IIRC when i asked this question a while back on the forum, the n-Vi doesn't follow the Naim source component ground approach, probably so it can be slotted into a full Naim system in AV bypass mode without upsetting the grounding scheme. Up until now I've never had any issues with ground loop induced noise in the system.

When the NDX arrived, i followed the guidelines in the manual and set the ground switch to chassis and left it at that. Come the weekend i needed to change the setting on our universal remote, as the NDX had taken over TV sound duties on the TiVo box from the n-Vi. Powering up the n-Vi to check the remote control settings for DVD produced an audible buzz through the speakers. Something that hadn't been an issue before the arrival of the NDX. I checked all the connections and suspecting a grounding issue, changed the ground switch on the NDX to floating which killed the buzz. Listening to the NDX later that day, something wasn't right - it sounded fine, but it's music making seemed to be lacking, missing a bit of bounce. I played a few tracks, then went and set the switch back to chassis and played the same tracks again. The bounce was back. Time to check my grounding.

With the n-Vi powered up again, and the XS in AV mode, the buzz is back. Unplugging the HDMI connection to the n-Vi kills the buzz so it seems to be an issue with a grounding on the HDMI side of the n-Vi. In my setup, the HDMI connection goes to a Geffen 3-1 HDMI switcher which also handles the output from the TiVo box, taking a single feed hidden in the wall to the TV. My concern was although the ground problem noise issue was fixed using the NDX switch, the earthing was less than optimum (being made on the 'noisy' side of the system) causing the loss in sound quality.

Due to the combination of potential ground sources on the video side of the n-Vi (TiVo box cable connection, plasma earth, HDMI switch earth) i couldn't easily sort this side out (and lifting safety earths isn't a good way of doing things) without pulling the rack to bits and checking grounding paths. The video side works fine so what i really needed to do was isolate the n-Vi from the XS, leaving the NDX to be the ground point.

Luckily the NDX comes to the rescue with its range of digital inputs but it only has one Toslink input which is already in use. Then i remember the white paper which mentions the coaxial digital inputs are transformer isolated so i can connect the n-Vi to the NDX via S/PDIF coax, getting rid of the analogue signal connection and keep galvanic isolation. A dig through my odd box of cables turns up a suitable RCA equipped 75 Ohm cable and a quick tweak of the n-Vi setup menu enables the digital output in PCM stereo mode. A check of all modes, and no buzz anymore and the NDX is singing.

I suspect that our recent move from a Virgin media V+ box to the TiVo may have changed the earthing setup - something i'll need to check as although the grounding issue is sorted due to isolation, i'd like to understand why i've not had this problem before with other sources which follow the Naim grounding policy.

James