sonos era 100 pair issue. plays from one speaker only

Do both work, as a stereo Pair, when streaming? If that works then try these:

Are you sure the 3.5 mm cable you are using is stereo? That it is fully seated in the 3.5 mm socket?

The line-in should show as active on either speaker, the one the adapter is plugged into.

If all that is good try swapping the right and left connectors on the 3.5 mm cable where they connect to the preamp.

Next try swapping at the input to the preamp, and last at the turntable.

Hi. 

Thanks for the reply. 

Both work as stereo pair when on Spotify. 

Will try switching cables again, tried previously as still the same, plays from non line in connected speaker  

Double check too that all app’s and devices are up to date. But my suspicion is a cable or a connector, or possibly the cables on the cartridge on the turntable. 

Make sure the cables are inserted the full amount, especially the 3.5 mm end into the adapter.  Also, check that your cables are stereo.  The 3.5 mm end should have two black bands (see right below) vs. one black band (see left):

Is the Rega pre-amp you refer to built-in or outboard. If the latter which model?

If pre-amp is built-in and the RCA’s are not hardwired you need a 3rd party RCA to 3.5mm cable to attach to the Sonos line-in adapter.

Otherwise please explain the Rega turntable and pre-amp configuration.

Thanks for all your replies. The pre amp is rega a2d. Not built in. Checked and is stereo connector. 

Have tried resetting the speakers. Pair. Unpair. 

Having no luck. 

Did you try unplugging and then reconnecting cables to ensure they’re fully seated? What happened when you switched the left and right rca connectors on the outputs on the preamp? Did you check the cartridge connections?