As I mentioned above, network issues can cause intermittent, and missing sound, not distortion. Cartridge miswiring can result in some of your observations. Speakers close together or a mono Room will exhibit more symptoms and headphones less symptoms of the type you are describing if they are due to cartridge miswiring. It’s very easy to check the wiring and this would be my first step If I had your symptoms. Since this is a vintage turntable, the miswiring could have occurred decades ago.

If this is a MM/MC spat, all attempts at playing would be equally effected.

Do things improve if all of these other Sonos speakers are placed in the same room - as a test - as the Sonos Amp that is delivering the complete signal to the passive speakers?

Of course, if there is a network issue it will manifest itself as stuttering or no music and not as poor sound quality. As said by others here.

@Kumar 

Actually yes. The One SLs, which sound fine are in the same room, but they only work when paired in stereo. The Beam sounds quite bad and is in another room. An Era 100 is in the furthest room and seemingly consequently, sounds the worst.

The thing is, my router is not in the same room (it's actually right beside the Beam), so how is distance relevant?

Also my Arc is in the same room as the Amp and it doesn't sound the same as the passive speakers. 

I have confirmed it is an MM cartridge and that my preamp is configured accordingly. But do you have another example of how it could be "miswired"? Do you mean in the turntable itself? Because I'm pretty sure that from the phono out to the Amp, it's wired correctly.

Last point first - Speakers sound different from each other; each has a sonic signature.

The distance is relevant because the other Sonos speakers are getting the sound from the turntable wirelessly from the Sonos Amp, not from the router.

As to the One SLs - if they sound fine getting the turntable signals wirelessly from the Sonos Amp, proof of concept of the turntable as a viable source to other than the passive speakers wired to the Amp, has been established.

Moving on:

I see no reason why the One SL should work only when paired in stereo. The typical problem is reversed - a single One will work fine, but when stereo paired, the other speaker in the pair may either not work, or may stutter. I don’t know how this is done these days, but in the past the solution to this issue would have been to run a diagnostic of speakers that are not working, and send the diagnostic number to Sonos support for troubleshooting. I suggest you do that for this pair.

And do the same as a separate complaint for the Era 100 and the Beam when they are playing. For these note that speakers stuttering due to a network issue is a valid complaint. Speakers sounding bad because you do not like their sound signature cannot be addressed except by a speaker change. Unless you are saying that the Era, for example, sounds fine when playing music from Spotify, but not when it is playing music from the turntable, wirelessly sent to it by the Sonos Amp. In which case, this is cause for a valid complaint to Sonos Support.

Check the wiring to the back of the cartridge in the turntable’s head shell.

Thanks. I'll try both of these.

@swisser 
I’ve been monitoring this thread. What puzzles me that no mention of the brand/model of the TT nor the Pre-Amp being used has been mentioned; nor asked for that matter  (unless I missed it) . Kind’a like going to the Doctor for pain relief and one fails to mention where the pain is felt. Can you please provide the Brand/model of the TT and Pre Amp.

The TT is a Thorens TD318. By "vintage" I just meant that it's not new and by the looks of it, it's from the early 90s. The preamp was a Pro-ject Phono Box, suitable for MM/MC. In my initial panic and stubbornness, I sent it back because I was sure it was the issue. In the meantime I bought a cheap one (LD Systems PPA2) but it showed the exact same symptoms. The weird thing is that they sent me back a NEW Pro-ject Phono Box, even though I'm now sure there was nothing wrong with the first one. So I've now tried three preamps and nothing has changed.

@swisser,

Do you notice any difference in the TT playback quality to other Sonos Rooms mentioned, if you adjust the ‘Audio Delay’ in the Amps ‘room’ settings? (Settings/System//Amp Room Name]/Audio Delay), aswell as increasing the line-in ‘Source Level’ in the Sonos App too.

I've also moved all my Sonos speakers around the apartment and placement makes absolutely no difference. This seems to also point to an issue in the TT.

I think this question has already been answered by @buzz but I'll ask again for clarity: If the turntable sounds fine through a traditional (no Sonos/streaming) set-up, also sounds fine through the Sonos Amp with passive speakers, is it still possible that there is an issue with the turntable?

The audio delay and source level settings unfortunately haven't changed anything. I have the level set to 10 now, but I've tried changing both of them every step of the way along with the compression setting

Have you tried generating a diagnostics and speaking to Sonos? That might identify/eliminate any issues with the Amp. 

I haven't yet, but I will tomorrow and update here.

It seems to me that the mono speakers are having the issue, not the stereo speakers. You can quickly test this by switching AMP to mono.

@buzz you nailed it. I hear no audio at all from the Amp when I switch it to mono. 

I'm a bit confused as to what this tells me though?

Check the cartridge wiring.

“Mono” adds the left and right channels of Line-In. If (+) and (-) wires are are mixed up for one channel, the sum is zero. I’m surprised that you have no sound when in mono, I would expect minimal sound and possibly some instruments cancelling, but we now know that there is an input issue for the turntable signal.

Worth testing that the sound is fine when the Amp is set to Mono mode.

If that works, and the TT works when played through a conventional amplifier,  then it would seem to suggest that the TT is ok.

Have you tried using the AMP as the source of a streaming service playing that through the passive speakers and then grouping the amp with your other devices. Next test would be to go to one of your other devices and select the line-in of the amp and see what the sound is like (do not play through the Amp).

You can generate diagnostics at any time just keep track of the scenario you were testing for each diagnostic. If you post the diagnostic numbers here Sonos staff may (but only may) look at them before you have a chance to call them.

I probably can’t add anything that can resolve your issue. However, I’ll share this information:

The Thorens TD318 was introduced in 1984. That said the Technology is 39 years old. All reviews I’ve read about the Thorens TD318 state that is an excellent TT and well worth keeping. The reviews also mentioned that it may perform better with a more modern cartridge and possibly different type of Pre-Amp vs the Project Mono Box and/or the LD Systems PPA2. More on that later.

I assume your basic setup is TT leads to Pre-amp In-put > Pre-Amp RCA-OUT > Sonos AMP RCA-IN > Passive speakers wired to L/R Sonos Amp Terminals. The Sonos Amp is set as a room/zone. If so by all that is Sonos your TT is properly setup and the sound should be great.

When Playing Vinyl the Sonos AMP with passive speakers should be set as the default room with Line-in  set to auto play in the Sonos App.

For reference my setup is a Sonos Project Debut Carbon TT with Sonos Amp, Cambridge Duo Pre-Amp, Definitive Technology D7 Series Book Shelf Speakers and Sonos Sub (G3). I’m able to start the music and group it to any Sonos speaker (Era 100’s in Stereo pair with sub, Arc HT with Era 100’s and sub, Arc HT with Era 300’s and sub & Era 300’s in stereo pair and sub) with no drops and/or static.

The only major difference I assume in our setup is the Cambridge Duo Pre-Amp. Click this link for info on Pre-Amp. As has been suggested submitting a diagnostic to Sonos may be your best course of action.

If this was the case would it not affect how the passive speaker pair wired to the Sonos Amp speaker terminals sounds when played in stereo mode?

SOLVED:

I'm feeling very dumb about this, but after examining the turntable leads for probably the third or fourth time, I noticed the tiniest piece of solder coming off the center pin of one of the coax connectors and just resting on the outer rim. Honestly, it was so small it just broke off when I blew on it.

That was super frustrating, but thank you all for your perseverance because I was convinced it was not an issue with the turntable- as I grew up in the CD era, I probably should have known better...

Side question- Is the Amp meant to run relatively hot? Because mine is.

Thanks.

Well spotted! And now, it’s sorted. How are you enjoying the sound? 

It sounds quite good overall. After this episode, I suspect there might but some other issues in the turntable, so I will probably give it a thorough once over now that I know there's nothing wrong with my actual set-up. At least it sounds the same on all devices now. And I'm still surprised at how differently each individual Sonos product got thrown off by some bad wiring. Especially considering it sounded fine on the Amp... 

The Era 100, which is quite far away from the Amp and router, seems to sometimes be cutting out intermittently (only on line-in). Is there any way to improve the signal without moving it closer?

That flake could have moved around, changing the symptoms, as you fussed with things.

Try the compressed setting for line in.