Sonos Amp and High level input from Subwooder?

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I have a Sonos Amp, and a Definitive Tech Sub Pro 800 that has both the mono RCA LFE option (What is connected now) and also has the option to connect via high level input. Real Subwoofers have this too.

Can this work with the Sonos Amp? I searched but did not find an answer. So basically I’d connect my Def Tech sub to the left and right speaker channels of the amp, and then I would connect my 2 front speakers to the back of the sub.

Will that work or do I have to keep using the LFE? It’s for music, so I figured using the High Level input may sound better as the sub would get the same signal as the speakers, right? Or am I mistaken?


Best answer by jgatie 10 April 2019, 14:28

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Hi @szymonmr 

What problem specifically did you solve by using Arrow?

I have a similar problem as discussed in this forum. I get a hum when connecting the Amp to a REL T5i using the high level inputs. When I use the RCA cable as indicated by REL the hum reduces massively but not completely. 

hi, i think i have a solution, rel arror solved the problem. Everything works great with sonos amp.

you tried to connect with rel arrow

thank you for the information
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Yeah that does reduce the hum to where it is barely noticeable but doesn’t eliminate it completely.  I haven’t yet tried just removing the ground prong from the sub’s power cable.  That would accomplish the same thing.  I just tried using one of these:

15 Amp Single Outlet Grounding Adapter UPC: 818897010022

It’s less than a buck if you want to give it a shot.  Still doesn’t really address the root issue, though and not sure if there’s any long-term concern running the sub without a ground.


I do not know if it works, I talked to the REL distributor today, he said to try connecting the subwoofer to a power outlet without grounding.

Thank you very much, I will also report to sonos.

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Hi szymonmr,

Still working with them.  I suggest you open a new case and reference my case # (01446377).  The more people that log similar cases, the more likely Sonos is to take this seriously and do something about it.

They haven’t let me speak to an actual engineer, but the support rep Jaymes has been very helpful in relaying information.

At this point, we’re in wait-and-see mode.  They have all the documentation to prove this is an actual issue and all I can do is hope they enable an always-on option like my NAD had (they have the NAD documentation as well).  This doesn’t really consume much more power (maybe .5-1 watt).  The REL sub just needs a small amount of current on the posts to complete the circuit and eliminate the hum when the Amp goes into idle mode (aka “standby”).


Hello, have you already received a reply from sonos?

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I’m having the same issue with my REL T/9i sub.  When the Sonos Amp goes into standby, 60hz hum ensues.  If I hit one of the Volume or Play/Pause buttons on the front of the Amp, the hum goes away for a few minutes but then returns.  While streaming music, there is no hum at all and sounds beautiful.

Before the Sonus Amp, The REL was connected to a NAD D7050 (same room, same wiring) and have reconnected it to make sure I didn’t cause the issue.  The issue is definitely with the way the Sonos cuts signal to the outputs when in standby.  Basically, the “loop” between +/- in the high-level output is cut, so we end up with a ground loop.  If Sonos could provide an option/setting to enable signal to the outputs when in standby, this would solve the issue.  As the OP mentioned, using the low-level RCA connector is low gain and does not sound anywhere close to as good as using the high-level inputs on the REL.

I have a support ticket logged with Sonos to talk to an engineer.  Will let everyone know how that goes.  In the meantime, I have a workaround that makes the standby hum go away:

  1. Connect the high-level wires like normal (Sonos Right-Red, Left Red, Left-Black to REL Red, Yellow and Black respectively)
  2. Connect an RCA cable from the Sonus Sub output to the REL LFE/.1 port
  3. Go into the Sonus App: Settings → System → <Your Room Name> Amp → Sub Audio and turn off the “Sub” selector at the top.
  4. When listening to music, turn the LFE dial all the way down.
  5. When not listening to music, turn the LFE selector up until the hum goes away.  For me, this is 8 clicks.  Note that the hum may get louder as you turn the dial until you hit the magic spot and hum will go away.

Hope this helps those with the same issue until a permanent solution is available. 

Guys forget it, it was the sonos sub on 0 iso 180 so it was cancelling the other bass, loads of bass now, ao forget about the extra sub on the AMP Sonos (when in correct fase and position) is amazing
I think i found it, sonos amp only has a single mono sub out, and the purple line in on my TS11 sub is for LFE only!! Low frequency effect, Sonos amp does not send digital processed audio through that port! The manual of the Harman TS11 Sub reads this: if the receiver has only 1 port for sub out, connect the single cable either to the left or right line in!!!

Same issue here guys, i have the Sonos AMP hooked up to 2 kef r300’s and i get decent 50hz bass, when i add the sonos sub, i find that the Sonos sub is not at all a musical sub sound, clonky. So i tried to add my ST11 Sub from Harman Kardon (200watt 10”) connected it to the purple tulip sockets. And almost no sound was coming out no matter what i played. Then i turned the crossover up a bit, to 100hz still not much. Then i turned the sub itself to the max value (analogue knob on the sub itself) then a little sound came out. I am used to play this sub with my onkyo txnr616 and i had rich bass even when the knob on the sub was set to 20%!!! So why is the sub out of the Sonos AMP so silent when it comes to outputting sub? What am i doing wrong? Sonos support doesnt know anything about this, cant help. I thought it was plug and play and bang i would have the Onkyo loud sub bass in my room, but its not even getting close!!! Its super silent... is this port not powerful enough? Am i connecting the ST11 wrongly? Who can help me out?
In many respects, Sonos product design is for a target market that does not want/need such information or flexibility. Which is why audiophiles won't buy into Sonos, but I don't think Sonos cares about the consequent loss of that little market.
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I remember seeing that the Sonos Amp offers this option for third party Subs as well, so that should address your needs. I can't see that much would be lost regardless of how capable the main speakers are for low frequencies, if the crossover is set to as low as 50hz.
Yes, the amp does work with 3rd party subs this way. That is how I am using it, with the 50hz crossover setting (my main speakers go to about 45Hz). But with main speakers that go a little lower than this I might not want to run it this way. I appreciate when manufacturers try to give customers as much flexibility as reasonably possible, and also when they are open about providing technical information. I think Sonos comes up short here, even though I have been happy with their products.
I just don't understand why Sonos would not have the option to output full range to the main speakers with sub output connected.
No idea; it isn't there in the Connect Amp either. And in the Connect Amp, the crossover is set at 80hz, no choices; of course if a Sonos Sub is being added, crossover can be chosen from 50Hz to 110 Hz. I remember seeing that the Sonos Amp offers this option for third party Subs as well, so that should address your needs. I can't see that much would be lost regardless of how capable the main speakers are for low frequencies, if the crossover is set to as low as 50hz.
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Just curious; why do you need this? To present the main speakers with the full signal or to do the same to the Sub, using the Sub crossover for filtering?
And for getting either/both, won't high level connections work - the REL seems to have hum issues with these, but that seems to be a REL thing, not one related to high level connections as such.

I like to cross over with a sub as low as possible, if main speakers go there. If they roll off smoothly at the low end then I just cross over using the filter in the sub while feeding main speakers full range. As you say, an option with the Sonos Amp is to feed the sub a speaker level signal to do this. But that is not always the nicest option, Or there might be a problem with this, like hum that the OP of this thread is having. I just don't understand why Sonos would not have the option to output full range to the main speakers with sub output connected.
Just curious; why do you need this? To present the main speakers with the full signal or to do the same to the Sub, using the Sub crossover for filtering?
And for getting either/both, won't high level connections work - the REL seems to have hum issues with these, but that seems to be a REL thing, not one related to high level connections as such.
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Just my opinion, but I I find fault with Sonos for not allowing the sub output to be used without engaging the crossover. They could easily fix that with a firmware update, I would think. Maybe they will if enough people bug them. I sent an email asking for this a month or two ago.
No idea; I haven't used REL. The only additional information I have gleaned is that where the Sonos Amp is concerned, the frequency stripping at the speaker terminals happens only if something is plugged into the Sub out on the Amp AND that Sub is turned on in the Sonos app, under settings for the Amp in room settings. Even if that something is just a blank jack. So if you make sure that the Sub is turned off, you should not lose anything by wiring the Sub out to the LFE in as suggested by REL for hum elimination. If you do this, and let the black lead of REL float unconnected, according to REL there should be no hum for high level connections to class D amps like the Sonos Amp.
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So i've not had luck with the high level connection, still getting a hum regardless of how I tried to do the ground.

I'm testing between using the Low level connection, and the LFE now to the Amp Sub out.

The only issue I have with the low level connection, is that the bass and gain seem to be considerably lower than the LFE, not sure yet if it's normal or just has to be turned up a bit.

I know theoretically LFE is for movies, but I'll see what type of bass response it gives me and if I can still adjust crossover. (The app allows me to, just need to confirm by listening that's working)

I wonder what are the downsides of using LFE for music, aside from the crossover being at 80hz? Does it strip out any other things?
More intriguing results on googling from REL:

I know that this link does not refer to your specific model and this is referenced in the linked article, but I have not been able to find the link for another article mentioned that does.

But this one is interesting because it says that with Sonos, only a low level connection is recommended.

I also think that the article is not being completely honest is using as an excuse the Sonos lack of Hi Res capability to say that if you use low level connection, it is still ok because Sonos does not go the distance anyway as far as sound quality is concerned, so what is a little loss of Sub integration quality by using the low level connection? Hogwash, that excuse.

It seems to me that REL and Sonos are not a happy pairing. Perhaps due to the Sonos sleep mode feature as the article suggests, perhaps something else. After all this research I would not use REL with Sonos kit. In any case, I use the Sonos Sub for music and it does all I expect a Sub to, bonded to a play 1 pair.
This, from the horse's mouth:

Also see if the hum goes away by connecting both the amp and the REL to the same wall power socket, and stays away without the cable from the LFE to the Amp.
It might be useful to open a thread here on the following question:

What happens at the speaker terminals of the Sonos Amp if a blank jack is plugged into the Sub out jack? Are the speaker terminals then denied frequencies below the crossover setting of 80Hz even if there is nothing at the other end of the jack? And then does turning the Sub on/off in room settings for the Sonos amp in the Sonos app have any impact on what happens at the speaker terminals? Are low frequencies restored to the speaker terminals with the jack plugged in, but the Sub setting on off?

And/or pose this question in an email to Sonos Support.

All other questions are for REL to answer. But if you like the sound from the REL sub compared to the Sonos Sub, I would just keep listening to it and not overthink the matter.
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The only way I was able to get the hum to disappear while using the high level connection was:

Black ground to amp speaker negative
Rca cable from LFE on sub to the amp sub out

This exactly what REL says you should not do, as far as the first part is concerned, where class D amps are concerned, and Sonos Amp is from that class.
As to the RCA cable from LFE to the Amp, REL says that a RCA cable can be connected to any RCA jack on the Amp that is free, it need not be the Sub jack only. Grounding is done via the shielding on the RCA cable so plugging the RCA cable to the line in jack on the Amp should also work.
Above two points as per REL videos on how to connect their Sub to an amp. If this is not working for you, I suggest you ask REL for help and return the Sub if they cannot solve the problem, subject to the next paragraph:
Plugging anything, even a blank plug into the Sub out signals the Sonos Amp to strip out the lower frequencies from the Amp speaker terminals. You cannot bypass that - all that turning the Sub off in the Sonos options does is turn off the Sub; this is a new feature and I suspect it does not restore the full frequencies to the speaker terminals. But there is no harm in trying this and seeing if it changes the overall sound quality in a beneficial way. I believe it will not make any difference, but I could be wrong, because I do not have this feature on my Connect Amps.
I don't know why low level isn't working; another question for REL, that.

First, thank you for the detailed answers, I appreciate it.

I did also contact Rel and Sonos, Rel will get back to me after talking with an engineer. Seems like not many people have the new Sonos Amp and a Rel sub and have done this, or at least have not asked about it to them or online much.

To answer your question, using high level input I and lfe at the same time (They recommend having both, for movies and music i guess) and if I turn off “sub” in the Sonos app, I do get a difference in sound. Control seems to be reverted back to the sub, I can adjust the crossover and volume on the sub itself and it seems to be working. When I turn sub back on, it seems to add some sort of digital processing that changes the nature of the front speakers sounds.

The hum I am getting is audible if I turn the crossover up high, and when the sound is idle after playing. It auto standby after a few minutes and the humming seems to stop. The ground on or off, same result. RCA cable to lfe or Rca out, same result with high level. If I remove the Rca all together, I get extremely loud humming on the sub at all times.

I do have a Sonos Sub as well, but that’s paired with my 5.1 system and I do like the sound of this Rel for music, as that is what I use it exclusively for.