Differential Monoblocks with twin REL subs

However, there is a post marked as 'Ground' on the rear of teh Pre-amp, so I guess I can assume that this would do the trick as well? Can I connect both subs' black wire toteh same pre-amp ground post?

Although in some systems that approach will provide reasonable results, I would not recommend doing that in this case, at least without first making some multimeter measurements to see if that ground point is directly connected to the ground sleeve of the preamp's RCA output connectors. And looking at a photo of the rear panel of the preamp, which I found via Google, my guess is that it is not. Depending on the specifics of the designs, the result could conceivably be a big-time hum. Or even if that direct connection exists, you might still get a slight ground loop hum and/or slight sonic degradation.

Personally, I'd get an inexpensive multimeter to eliminate some of the guesswork, and some inexpensive Mogami Gold Studio balanced cables, and proceed as I indicated earlier. I wouldn't be surprised if you were to get better sonic results with those cables than with your present RCA cables, even if the RCA cables are far more expensive.

Regards,
-- Al

Heck I would just hook it up and see if it works. If it seems OK when you power up the subs, maybe it is. If there is a problem it will tell you right away and you turn it off and see what you can do.

Most subs that I have dealt with run right off the amplifier output terminals and don't interfere even if the output of the amplifier is floating (which ours are- we make fully differential amps).

I would thus not worry about the ground wire unless you encounter a hum.

Well, I have taken your advice and hooked it up. As discussed, I connected up the subs (yellow/red to +ve terminals, nothing to -ve, and black from both subs to the ground post on my pre-amp), and everything seems fine with absolutely no trace of hum at all.

And what a difference the subs make to the scale of the music! I had grown used to the bass limitations of the of the Magnepans, but after correcting my original temptation to krank up the bass (sounded fantastic for a while though), and some experimentation about where to position the frequency roll-off on the subs, the results have by a long way exceeded my expectations. Some more experimentation with positioning and in particular with the frequency roll off on the subs will probably be required over a period of a few weeks, but I am already convinced that the relatively small cost of the upgrade has been well and truly justified, and that the subs are here to stay.

Incidentally, I have also been in touch with a dealer (Hi-Fi of course) close to me who still keeps in touch with the amp's designer, and he has kindly offered to get me a definitive answer as to whether or not the amps truly are a differential design.

Lastly, Almarg, I have taken your advice that I should try a pair of Mogami balanced cables for the amps to replace my existing RCA leads. I can't resist giving this a go as well, so they are now on order. Hopefully my last 'upgrade' for a while.

Many thanks to all those who have helped, especially Almarg, and yes, I am now also the proud owner of a multimeter (thinking about going back to University to figure out how to use it properly though).

Hello,

The following is a response I received from REL:

Chip,
Connecting a pair of RELs to a balanced amp in stereo is only a little different form the standard REL connection scheme. Your subs should have come included with the REL High Level cable. That cable consists of three wires, Black, Yellow, and Red. The Red and Yellow are positive leads and eth Black wire is your ground lead. You need to pair the Red and Yellow wires from the first sub to a single positive binding post (right side). The Red and Yellow wires from the second sub will be paired together on the other positive binding post (left side). Both Black wires need to be attached to a dedicated ground post or chassis screw. You cannot connect the Black wires to a negative binding post because there is enough current on the negative side of a balanced amp to potentially damage eth ground circuit on the RELs.       

Paul Greene
Service Department Manager
SUMIKO | 2431 Fifth St | Berkeley, CA 94710
ph 510.843.4500 | fax 510.843.7120
www.sumikoaudio.net