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Help Please - Sonos Amp Sub Out with Buckeye NC502MP and passive sub


May 24, 2022
I could use some wisdom, please. I have been running a small patio 2.1 setup for 3+ years and it's been great. Sonos Amp powering a pair of Polk Atrium 6 and then sub out from Sonos to an old Polk SWA500 subwoofer amp and the polk amp wired (4 conductor) to a Polk Atrium Sub100 (dual 8ohm voice coils). It worked well.

Fast forward and I added a Buckeye NC502MPx4 to my home theater for LCR. (kicking myself for not buying the 6-channel now). So, I thought hey, why don't I get rid of this old ugly Polk SW amp and run the Sub100 off the Buckeye's 4th unused channel--I can use the Sonos app crossover and subwoofer "level control" settings, right? So, I gave it a shot and ran into what I suspect is line level voltage gain issues/mismatch. The sub works, but I now have to turn the Sonos app subwoofer level to somewhere around +12 to +15 (max) and it's still a little anemic. With the old Polk amp, I was typically around 0 to +2, but I had gain/volume control on the polk amp as well as the sonos app.

I've double-check wiring and even rewired down to a single pair of conductors from the Buckeye so that I'm running the DVC sub in parallel at 4ohms. I believe further evidence of possible gain structure issues is that when I turn the Sonos MV up, the subwoofer seems to come to life, but it's at a volume that I wouldn't typically listen at outside due to respect for neighbors.

What am I missing? Is there anything I could do to help resolve this? Was wondering about maybe a line level amplifier, but really hoping not to mess with that. I'd really like to avoid putting the polk amp back in my rack.

Would I be better served picking up a Buckeye NC252MP 2-channel (lower input sensitivity) and feeding the sub both channels, one per voice coil?

Thanks in advance for any suggestions or guidance.
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