Hi @minimalist,

I’ve had a look around and it seems you can just leave the grounding wire disconnected. If you run into any RF or 50/60 cycle noise issues, then you’ll want to look at connecting it to an un-used RCA port on the Sonos Port. 

This community thread has talk about this, but with the Sonos Amp, and explained how to connect the grounding wire if needed, however I think it’s still relevant:

And also here:

If the instructions don’t mention connecting the ground cable, then it’s likely not needed and just a general cable that Pro-Ject ship with all their turntables. Try without and see if you hear any noise/buzzing. If so, maybe these threads can help resolve that issue, if it arises.

I hope this information helps!

Thanks.  It does feel like it’s just the cable Pro-Ject ships with the turntable (which is really just a Pro-Ject Debut Carbon Esprit SB turntable with a phono preamp added to the Sonos edition).  I left it unconnected and it seems to work fine without it, no buzz or hum.

Even with the preamp set to “line” II did still have to turn the gain way up in the Sonos app to 9 out of 10 to make it play at the same levels Im accustomed to my streaming music to play at. But all in all it sound very nice.  Interestingly I don’t hear much difference between hooking it up to the Port (which is then connected to my AVR) and hooking it (old school) directly to the AVR.  

A ground is almost always required for the connection between the turntable arm and the phono preamp input. Grounds are rarely required between the preamp output and Line-In.

@buzz So it sounds like the ground is taken care of with the built in photo pre-amp and the cable is just a holdover from what’s in the box for a non preamp version of the DC Esprit SB turntables that Pro-Ject sells.

There is very little standardization here. Yes, they might have thrown in the ground wire without thinking. In some cases adding a ground wire will introduce hum, rather than eliminate it. In large studios and concert halls you’d hire a specialized consultant to come in and work out the grounding situation.

Don’t worry about the gain level set for Line-In unless you cannot achieve a usable output. Typical disc player output levels are very high, phono preamp levels not so high. Older European equipment line levels are low.