It should work.

1. Have you enabled Line-In Autoplay?
2. Does the turntable have a phono preamp?
3. Have you tried increasing the Line-In level setting?

Hi 

1. Yes
2. I have a Marantz TT5005, with inbuilt pre amp
3. I’ve also tried other level settings to no avail. 

I was having the same issue, got a Technics SL1210, into Preamp and into Sonos Amp, out to Play 1 abs One speakers. Autoplay wasn’t working - spoke on the chat, via email, and video examples of switching between streaming audio and then trying to use my turntable, Autoplay wasn’t working. after testing other line in sources to ensure Line In to see if Autoplay would work that way (if didn’t) I spoke with one of the Sonos advisors on the phone - we reduced the Line In Source Level from 10 down to 2 and Autoplay began working. We kept going until we got to Source Level 5 and Autoplay kept working. 
 

At the time (couple of weeks ago) I couldn’t even notice a difference in volume between streaming and Line In audio. However, I’ve just had to unplug my Amp and have now noticed volume is really low when going from streaming audio to my turntable’s audio. So not entirely sure what is happening how. 
 

In short, if the Source Level is too high, try dropping it down, close the app, reopen to check the settings have saved abs try again and see if Autoplay works. 

Thanks. 
 

I have changed the level down from 10 through to 1.  To no avail. 
Bear in mind, I am trying to get Autoplay to work on the turntable while I’m watching tv (which is connected to the amp via hdmi arc. The only way I can get the turntable to work is by selecting the turntable via input services. 

Hi @Cr1st0f001 

Welcome to the Sonos Community!

Are you still experiencing this issue?

Your last statement is key - the Autoplay for your HDMI input is overriding the Autoplay for your Line-In. This is expected behaviour and will continue as long as the TV is on. You should find that if the TV is off and you’re listening to a streaming service or Music Library, playing a record on the turntable will make the Amp switch source automatically. If this is not the case, please get in touch with our technical support team. 

There’s more details on this post: 

Just tested this. Started playing a track via Spotify, then put a record on. It worked . The volume was way loud though. 

Hi @Cr1st0f001 

Thanks for keeping us posted with your results.

I recommend you adjust the Line In levels again until switching between sources isn’t so jarring. Bear in mind that the TV source isn’t good for this as changing channels and content can vary the volume by annoying amounts. Best for you to switch between Spotify and Line-In for comparison.

In settings under Autoplay you can set a default volume level.  Right now it might be set too loud.  
 

There is also in settings under Line-in, a Source-level setting which should be adjusted.  I matched it somewhat close to the level I get when streaming.  Corey alluded to that in his post.