Sonos Amp and real low-level support for subwoofer?

If your sub can take high level outputs from the amp speaker terminals, you can use these.

That was my primary plan, and what the sub manufacturer (Rel) recommends, but i’m getting an annoying hum that I can’t get rid of. Grounding the sub to the amp got rid of the loud low frequency hum, but there’s still a more high pitched hum left, which I don’t get when I connect low level.

I had a quick look at the linked thread that discusses the hum issue with REL/Sonos. It may give some useful suggestions, but not fully conclusive I suspect. Worth a look:

https://en.community.sonos.com/components-228996/sonos-amp-and-high-level-input-from-subwooder-6822917/index3.html

From the link: try connecting the REL Sub to a power socket that does not have an earth jack.

Yup, I’ve tried both grounded- and non-grounded power outlets. I also read the entire thread you linked to and I have spoken to Rel support and my grounding should be correctly set up. I even tried Rel’s wireless module that is also connected via high level. Then ground is not applicable since there’s no galvanic connection between Amp and sub, but the high pitched hum is still there.

I don’t see Sonos taking time to implement a bypassable filter for the sub out. So if the hum does not go, and you must have a Sub, another amp that does not cause hum may be the only option. If you still want a Sonos front end, adding a Port to such an amp would be the way to go then.

Or, try a sub from some other make than REL.

Yes, I’m considering both options. I chose the Sonos Amp over a Port + traditional amp for the small footprint and ease of use (this is my living room/family stereo setup), but there’s obviously some trade-offs. I might try another sub brand, like an SVS, to see if it works better, it’s just and that I’m using this 100% for music and the Rel integrates fantastically with my main speakers. But sometimes you just can’t get it all. :)

In your place I would even reconsider the presence of the Sub itself, if the main speakers go down as low as you say they do. But if you must have one, integration is all important where music is concerned, so another amp of small footprint? And why must you have Sonos at all, unless you want to integrate with other rooms?

I have small bookshelf speakers (Guru Junior) that can go very low for its size (34 Hz at -6 db). But I would still like a bit of more bottom in the low end. And yes, my living room is part of a multi room setup.

I can of course live without the sub, it just sounds fuller and better with it. Not sure it’s worth the cost of the sub itself AND a new amplifier though. Will need to think about it for a while.

That actually isn't very low...more relevant is the -3dB number which may well be in the region of 50Hz. I assume you have tried using the Sonos amp Sub out into the low level input on the REL, with the crossover on the amp set to 50Hz. What do you find lacking in that configuration?