M700 + REL Subwoofer high level input question

Hi all. I am new here. And recently I just ordered a pair of M700. The M700 will be driving my ATC SCM11 speakers and I have an old REL Strata II which I intend to continue to use it.

My question is can I use the same high level input for the REL with a Class D amp like the M700? I read somewhere there’ll be some ground loop hum issue. Is there a way that I can still enjoy using my REL and the M700 using the high level input?


Maybe start here. I used one and no issues.

Since you already own the REL there is no harm in following the directions and setting it up the way the directions state. I can tell you that I followed their directions for a differentially balanced integrated amp and had a hum issue whenever the integrated was switched to standby because doing so lifted the ground and caused a hum issue. The only way around it was to shut down the subs when the integrated was in standby or just live with it.

I had a similar issue with my BHK 250 amp and REL S/5 SHO when the amp was put in standby that was solved by a resistor network from REL (cost $100) that connects to a chassis binding post provided by PSA (free). I don’t know if they have a similar thing for the M700’s but if a hum develops it’s worth inquiring.

Interesting. They never offered this to me. I returned the sub.

If I remember right, I connected to + on one amp and - on the other and left the black wire disconnected. No hum, all worked fine. I believe I remember a REL tech told me if I did get hum, run an RCA from my pre to the REL and that would satisfy the ground issue. never needed to try that. And, That was a while back. Still considering a REL but I have a different amp now (however I miss my 700s)…

My sense was that PSA worked with REL. The network (which just looked like wire Y adapters that connected the binding post on the chassis to the left and right speaker binding posts–I did not try to measure the resistors that must have been built-in) was specifically for the BHK 250 (at least the instructions showed the BHK 250). The dealer from whom I bought the REL made the inquiries and got the network for me. Probably didn’t hurt that Paul is a vocal REL fan.

So are you (we) saying a REL will not hook up easy (to a 250) just like with any A/B amp I have used? I’ll need a resistor network? I have not found my REL yet so this is interesting to know.

I was expecting the hum issue because others on the forum had reported it. You may not get hum at all depending on your configuration. If you do get hum from your REL with a BHK 250, the network is an easy fix. The hum only occurs using high-level (speaker post) connections and only when the amp is put in standby. Even without the network there was no hum when the amp was fully on.

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I don’t think it’s hum when the amp is operational. It’s when the amp is in standby that the hum presents itself. It least that was my case. When I put my amp in standby (off) it lifted ground which ended up causing a hum. Yes I ran the the RCA line and everything REL recommended. I got a slight hum every time I turned my amp to standby.

Got it thanks. I am definitely going hi-level the way I have hooked up previously. Sounds like easy to determine and easy to rectify if needed.

I have a BHK 250 with a REL S/5 connected with the supplied high level cable. Yellow to Left Positive, Red to Right Positive and Black to the PS Audio supplied chassis lug. Power cable to the REL sub is connected to a power filter. There is a 12 volt trigger from my preamp to the BHK 250 and the power conditioner that turns the outlet for the subwoofer on and off with a 12 second delay. I get about 12 seconds of hum while the BHK is warming up before it comes out of standby, and 12 seconds of hum when the BHK goes into standby until the power outlet for the sub switches off.

If you had separate programmable on/off times on the sub power outlet, you could wait until the power amp comes out of standby to turn on the sub, and then turn off the sub before the amp goes back to standby.

FYI - There are other threads here discussing this problem. I have a REL T-9 and a GCD/M700 combo. I followed the REL instructions provided in roninaudio’s post above. I connected the T-9’s .1/LFE input to an open input RCA on my GCD using a male-to-male RCA cable. The RCA cable can be any cheap cable - it’s just providing a ground. Works perfectly.

In another thread another M700 owner followed the instructions in the REL manual. Attach Red to one mono positive speaker post and the yellow to the other mono’s positive speaker post. He attached the black to one of the mono’s chassis by loosening a chassis screw and poking the black wire into the gap between the chassis top and back panels. It worked for him. Hope this helps.

REL also has an article on its website discussing connections to a Class D Amp. REL Article - Connect to Class D Gear .

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I purchased a pair of M700’s this weekend with a Demo P5. I have a Rel R328 that I’ve used in my past systems that I absolutely love. I was hesitant to plugging everything in and worrying about the possibility of humming coming from the subwoofer. Unfortunately I have some problems with the P5, so I hooked everything with a standard power strip. One wire from the sub goes to each positive terminal of the amplifiers and the black ground wire, do nothing with it. Walla, no hum, buzz or feedback. Perfect, with power on or off, dead silent for me.

I leave everything on 24/7 including amps, sub and DAC (DirectStream). I hope this helps others who were wondering about the connection issues.

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I wonder this can possibly be a solution for hum problem? Just connect the black ( ground ) wire of the high output cable to this ground box.

I’m about to buy a REL as well and I have BHK 250. Can you describe or provide a link for the resistor network? That would be much appreciated. Thanks!

I don’t have a link. My dealer took care of it. The instructions refer specifically to the BHK 250 so if you or your dealer contact REL they should know exactly what you need. I think it had to be made to order. I don’t know if it is the same network for all RELs, or if it is needed for all models. I’d suggest contacting REL.

Here’s an update. I have finally hooked up my REL with the M700 by not connecting the ground wire. Works ok no hum.

Yay!!! Nice work and I’ll bet it sounds great.