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Hi all, 

Thanks in advance for any help you can offer. I’ve seen another post that never got resolved, so hoping to finally nail this one. 

The setup is simple. Sonos amp connected to two speakers (working perfectly), and a sub RCA line which is split into two RCA going into a FOSI subwoofer amp. I don’t know why, but the Sonos AMP is just not passing a signal to the FOSI.

 

I can confirm that everyting from FOSI to the sub is working correctly, as if I play music via bluetooth to the FOSI (it is a BT receiver as well) the sub functions well. I have confirmed that when trying to use the Sonos AMP I have the FOSI set to the connected inputs and not BT, so it’s not that. 

 

So…. any ideas? Oh, and I turned on the SUB option in the Sonos App, so it should be functioning properly. 

 

Thanks so much for any thoughts. 

Seems like there are 3 potential points of failure here.

1 - The amp isn’t sending output to the sub.  Do you have another sub or something that can take input from the RCAs and see if you get audio?  I’m not sure if any with RCA input would work, but it seems like it should still play some of the lower frequencies to confirm operation.

 

2 - You have a bad cable.  This seems like the likely issue.  Again not an expert on this, but sub cables I’ve used in the past (it’s been awhile) did not split into two channels.  Just a single channel connected to either left or right RCA depending on what the sub/sub manual stated.  I would try using a different cable, or use the cable with a different amp to test.

3 - The sub amp isn’t taking audio through the input.  The first test will also help figure if this is the issue.  If the Amp and cable work with another output device, then your sub amp is the issue.

Thanks for the reply Danny!

All are very good ideas. I don’t have any RCA speakers hanging around these days, but your suggestion made me think that I should use my high quality multimeter to see if any current is even getting through the cable. 

The cable I’m using is this
https://www.amazon.com/gp/product/B0B51416ZM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
Which seemed like the right thing, but perhaps not. Anyway, I’ll try the multimeter and report back. I also just thought to try a different output (I have headphone → RCA) and can just see if the sub is receiving and processing a signal. 

Thanks again!!!

It could very well be that the split cable is attenuating the signal enough to be below the level that wakes up the amplifier.  Usually a sub with two inputs has one that is used with a single sub out.  The other is for twin sub outputs.  I’d try it with a non-split RCA cable into one channel on the Amp. 

Does AMP acknowledge that something is connected to subwoofer output? AMP incorporates a detector switch. If the RCA plug is not inserted far enough the switch will not be triggered.

Hi buzz, thanks for the comment. How would I know if it acknowledges the subwoofer output? If the answer is because the subwoofer menu becomes available, then yes, it does know that something is connected. 

Just turning the gain up on the sub and touching the RCA connector you should hear something, which proves your sub is working.

Using the RCA to my sub I dislike how it filters what goes to my speakers.

I prefer the sound of using high level connection but the hum I get is too annoying 

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