HI @a_d_t,

Welcome to the Sonos community and for letting us know about your concern. Let me share some information with you. 

In connecting a third-party subwoofer, the Connect Amp has an auto-detecting RCA-type subwoofer output with an 80Hz crossover. Simply connect your subwoofer to the Connect Amp’s RCA output labeled SUB. Note that the Subwoofer and Line-In connections are disabled when Connect Amp is used as surrounds. To check if Sub line-in is being detected by the Connect Amp, I'll be requesting a diagnostic report submitted from your Sonos system. Please don't forget to include the confirmation number in your response to look into your system and find out the cause. 

We can wait for suggestions and feedback from our Sonos community members, they might provide additional information about this. Please do not hesitate to reach out if you have further questions or concerns. We are always happy to help out.

Hi Rowena,

Thank you for your help.

i can confirm I’ve connected the 3rd party sub using the RCA connector labelled subwoofer. It’s actually a ZP120 though it shows up under system information as a connect:amp.

My diagnostic reference is 473088467.

Hi @a_d_t, 

Thanks for your response and for submitting the diagnostic. Upon checking the report, your Connect Amp detected a Sub port connection. 

Let me suggest the next troubleshooting steps to isolate the issue and see if it works for you.

1. Reboot Sonos Connect Amp
   • Unplug and replug the RCA cable from the Sub port
   • Unplug your Sonos Connect Amp from the power and wait 30 seconds before you plug it back in.
   • Once your Connect Amp is back online, reconnect the RCA cable and test the audio.
2. Try another RCA cable if available
3. Connect your bass guitar combo to a non-Sonos device and see if it will work.

If it's still not working, I'd recommend contacting our phone support team to help you out. Please let me know if you have any questions or other concerns, we'll be glad to assist you.

Thanks. One question- if the ZP120 has detected the Sub port connection, should it give me some controls for the sub? If so, where in the app should I find them?

Hi @a_d_t, thank you for your response. In the Sonos app, you can enable Autoplay room to automatically play Line-In audio when Sonos detects a signal is being sent to the Line-In port. Here you can choose to Include Grouped Rooms and set an autoplay volume level. Autoplay is disabled by default. I’d also recommend reaching out to your bass guitar combo manufacturer to check for settings and configurations how will it work with other devices. If you need help with any other information, feel free to reach out.