Yes, thanks. But not RELs, per their connection guide, page 16. I’ve never understood the electrical reasoning here, but I do recall seeing a discussion here on the forum. I hear you, that you’re doing exactly that (one sub with M700 monoblocs). But for some reason REL prefers you not do that …
I found more than one discussion that touches on this topic, here’s one:
From what I gathered from fast skimming, lo output vs high output connections are involved. (?)
I remember that conflicting information. But here’s a video from last year where Paul explains how a single REL sub is connected to M700’s. Paul says he does it without any problems and virtually endorses it. https://www.youtube.com/watch?v=AGMB3xoLAbE
I float the REL ground wire (black) and connect the red to one mono positive and yellow to the other mono. If I can find the REL video showing this very hookup I’ll share it later.
You can also call REL support and they will walk you through it. I’ve been using it this way for 5 years with no hum, no harm, and great sound!
Thank you, that’s a great workaround to be aware of!
While that connection type may work, it is not REL’s recommended for balanced mono amplifiers such as the M700s.
If I were going to sum the channels, I believe the preferred connection would be RCA connections using a Y-adaptor from the preamp to sum the channels to mono.
In most things audio there are multiple ways to do things, but often the manufacturer’s recommendations should be followed.
It’s a good point, but I trust my 5-year trouble-free experience and Paul’s recent recommendation. I’m still looking for REL’s video showing the floating ground on balanced monos. At one time they supported it publicly.
I would guess that it is in the manufacturer’s best interest to recommend buying 2 REL subs… 
I had that ‘why buy a second sub belief’ and now, after adding a second, a lot opened up in my system. If you can afford it, do get a 2nd or at least demo a 2nd.
I’ll consider that advice!
With a balanced amplifier one always needs to “float” the ground because the negative terminal on the amplifier is not a “ground”, but carries signal opposite to the positive terminal.
Glad your system is working for you, but it is not considered best practice. There are multiple references to connecting balanced monobloc amplifiers in REL internet posts, and including in REL’s owners manuals.
A balanced amplifier is a different beast and requires different wiring conventions.
I may not have understood your comments, my apologies. M700 is a balanced amplifier IIRC, and because the REL manual has references to connecting balanced monobloc amps then isn’t that a valid and supported option? As well as Paul supporting that connection as well?
If we are talking best practice, then I understand that there is possibly a better setup. But if we are talking valid, supported, and usable options, then I should think that the floating ground connection can be recommended on this forum as one legitimate option.
Thoughts?
You are correct. With a balanced amplifier such as the M700, the ground wire from the REL definitely needs to “float”.
My point is this: not knowing the internal wiring of the REL at the speakon connection, and based on their instructions for wiring from monobloc amplifiers speaker connections, if I were going to sum the output to the woofer to mono I would choose to use the line level output from the preamp delivered via a y-adaptor rather than the amplifier speaker connection as a best practice for a single sub from monobloc amps.
No worries if it works for you, there are a lot of ways to skin a cat in audio connections. REL themselves continue to recommend a subwoofer for each channel when using the speaker level connections on monobloc amps.
I’m sorry if I offended you.
A further thought. And I am just wondering because I don’t have the engineering chops to know the answer to this question.
It would seem to me that if you connect both monobloc amplifiers to the speaker level input on the REL that you are effectively “bridging” the outputs of the M700s into the REL which could possibly cause an impedence mismatch or other issues.
When you bridge a stereo amp to mono (if allowed) the 8 ohm tap becomes 4 ohms, and the 4 ohm tap becomes 2 ohms which can cause stability issues under certain conditions.
I dunno. I’m sure PS or REL could provide insight.
No offense at all! You cleared up my confusion and were very helpful in explaining your perspective. I do apologize as it seems I might have come off annoyed - that was not what I intended. It’d be great if @Paul could clarify why he approved the single REL connection to M700s via High output by floating the ground and how that does not cause stability issues in his opinion.
I can confirm that floating the ground wire with balanced monoblocks works flawlessly.
In the rare case where hum is induced, attaching the black ground wire to a chassis screw is a safe solution.
My guess is that REL simply found it less of a load on customer-facing resources to simply recommend using the RCA inputs over high level, though this assumes that there is a line level RCS output, and very few more modestly priced preamps or integrated amps offer such…
I am here. I am confused as to what you’re asking. If you connect a REL sub to a balanced output amplifier like that of the M700, you definitely need to make sure the REL cable is not grounded. That is because the +/- outputs of an M700 are both hot with signal. So, yes, you float the ground wire (or connect it to the chassis) but make sure the two signal wires do not touch ground. Hope I am understanding the question.
Oof, that reminds me of the year I inadvertently shut down a room (for the rest of the weekend) at AXPONA. Pre-COVID. This was for Gayle Sanders’ new company, Eikon Audio, which were a five-way speaker system that used DSP and room monitoring, via a proprietary preamp which sent the signals to the speakers (which had onboard amps) to work their magic. (I can’t go into it fully here, other than to say Gayle’s design provided the same type of uniform wave launch that his electrostatic designs offered with Martin-Logan.) That year, they had two rooms next to each other.
While listening in one of the rooms, I noticed the image was pulled to the right. I pointed it out to Gayle and he also noticed it. I didn’t have time to return to the rooms that year but ran into him at the next show. Turns out they shut down that room as they couldn’t find the problem right away. It ended up being something simple–one of the five interconnects for the speaker had gotten an intermittent connection.
Post-COVID, I haven’t seen or hear anything from the company, and the domain for the site now points to a pro audio company. A shame, since I really liked the product, and Gayle is always so easygoing and friendly to speak with!
I was at that show and heard that system, and in fact spent some time after hours listening and chatting with Gayle. I thought they were quite remarkable, and agree he’s a friendly, pleasant fellow to speak with.
Indeed he is. I enjoyed him telling me about the custom Martin-Logan Summit speakers he had custom made for his retirement, and a few other audio-related things we chatted about. I’m glad Frank had an opportunity to interview him for Copper a couple of years ago.
Digging a little, the eikonaudio.com domain is dead, and there hasn’t been a social media post since 2022 from Eikon. That doesn’t bode well.