REL subwoofer hum

I own a REL stadium III, and have owned it for some time now. Just recently I noticed that it will produce an audible (although low level) hum when I turn my system’s amplifier off. I have the Stadium hooked up in the recommended manner: I have it hooked up with the neutrik cable to the Speaker B terminals of my amplifier. Speaker A terminals are occupied by my Sonus Faber concertos. When both sets of speaker terminals are on, the sub is quiet. When I turn off the B speaker terminals, or turn off the amp altogether, a low level Hum is output by the REL. I have not noticed this hum before and believe it to be a new occurrence. However, I guess it could be a ground hum. My main amplifier, and the REL are plugged into two different outlets, both outlets have quality AC filters/surge protectors, and I use the stock power cords for the amp and REL. Should I alter my hookup method? Would better power cables help? I really don’t want to have the REL serviced as, I’m sure you know, it weighs 110 pounds, and I don’t want to have to move it. If it is a so-called "ground hum", how do I alleviate it?

If the hum only happens when you turn off your main amp and is not present when all components are fully powered, then the hum is normal and not a problem. I'm not sure about the technical explanation, but this happens with every powered sub I've ever had.
Try connecting the ground to the amp chassis instead of the negative speaker terminal.This cured the hum in my REL,Art Audio setup.
Is that 100% safe?
I second Jw61's answer. I did the the same with my REL an it took care of the hum. Ken
Man, I was tearing my hair out over this hum problem and your suggestion solved it! I tried swapping cables, outlets, even swapping subwoofers (I have several RELs).
Do you think it is good practice in general to use the chassis ground instead of the speaker black terminal?
Mine has a hum all the time and my amp chassis doesn't have a ground on it. What to do? Called Sumiko once and they told me to unscrew one of the screws on my amp to connect. Called the amp manufacturer who said that would immediately void my warranty.
Alas, I still do have a slight hum under the one circumstance that you describe: when the amp is powered off and the sub is powered on. Not a huge problem of course but disappointing.
Hi there i have the same problem with my Musical Fidelity Kw -500 using a Rel R-305 subwoofer , turn the Musical Fidelity of and the hum starts turn it back on and i wait 30 seconds for the preamp section to kick in and the hum goes and the Rel works as per normal , i use the speakon connector , strange thing is i have also got a Redgum Audio RGI - 120 Integrated amplifier as a spare and when i connect it up the same as the Musical fidelity Kw -500 i have no problems and the Rel has no hum , so my hum problem is isolated to the Musical Fidelity integrated and i have also tried grounding it to the chasiss to no avail . Anyone had a problem with hum on M/F amps ?
60hz hum or what some call a ground loop problem is common with subs . Audioquest has a sub interconnect that has a ground lug built in , it solved the problem for me . I've not heard of chassis grounds ever harming a component or causing a warranty problem .
Floyd Toole said everything should be grounded to the preamp , to get the lowest noise floor possible .
I tried again with another wire combination on the
M/F kw 500 , as per the Rel manual : red wire to right channel positive , yellow wire to left channel positive and black wire to negative left channel . I found that if i connect all 3 wires to either the left or right channel the hum stops when the m/f is powered down and runs as per normal when powered up Rel appears to operate fine , would this be due to it having a bridged/dual differential internal design , apparently both left and right channels are
open/hot aand feature a bridged output.
I have removed the hum when the Kw -500 is turned of by connecting the 3 wires of the speakon connector to one channel of the musical fidelity , instead of running the red wire to the left channel i have connected red and yellow to the right channel along with the black ground wire. Not sure if this is an acceptable solution but does not appear to be having a negative affect on the amplifier
So all 3 wires are now connected to the right channel and no hum when powered down and m/f and rel works as normal when powered up.
I have the same problem. I have a new rel g1. Expensive sub for sure. Talked to sumiko and they helped but still have that dam hum. I've tried everything. Using ayre mono mxr. Fully balanced system. Even when I ground to preamplifier. Still get the hum. Im about to build out a critical listening room. In the design stage so I might just have to deal with this. I hope the rel is wired wrong on the inside. Any help.
We had enough clients with this humm problem and others like; distorted audio, static noise.

Unresolved by REL we recently traced out and examined the schematic and found several simple mistakes.

About the humm. The balanced speaker level input is simply miss designed. As a result it does not reject noise or hum. Solved

If using the high level input, there is distortion at anything above watt. A second design flaw, solved.

At high levels using any input the sub sounds like the amp is clipping or the woofer is bad. It can even sound like a flimsy cabinet. A third design flaw limits undistorted ouput to few watts. Again solved.

The woofer, amp and enclosure are fabulous. Once the electronics are overhauled the sound is too.
Had similar problem and was convinced it was some high priced item but it ended up being my DVR.

My Stadium III with speakon is silent.
I have all Krell with a Rel R328 with no hum at all.
I have had similar problems with my REL G1 subs to what Chrisautosound has described. I have been through 3 subs. The first 2 subs had loud distortion while playing music when phase was switched to 180. OK with 0 phase setting. With LFE, there is loud distortion when any low sounds are played. Volume does not need to be very loud.
Chrisautosound, what did you do to correct these problems?
REL/Sumiko has given me a third sub which appears to be functioning properly. They are sending me an new amp board for my second sub.
Steam3642 - Great advice. I've been fighting this with my Strata iii and BAT VK75SE (only a problem when amp is ON). The BAT is also fully balanced dual differential and when I wired to right terminals only, buz is gone and bass notes from sub come through clean and pure . . .Thanks!