How to connect monoblocks to a single REL sub with ONE RCA input


I just purchased two Quicksilver 60w Monoblock amplifiers and a LineStage Preamp by QS.
To connect this REL 328, normally one uses connect their Speakon cable (Red, Yellow, Black ends that connect to Right+, Left+, and Ground) or a SINGLE "low-level" RCA in. But this preamp doesn’t have a single sub out.

REL’s advice is to buy a second sub and attach one sub to each monoblock. Well, maybe I’ll do that, but in the meantime, I’d like to be able to hook up what I have.

Should I orient the amps so that the speaker terminals are close enough together to attach the strands of the Speakon cables? I have been warned by REL not to hook up high level to monoblocks because it will create a ground problem.

An alternative is that I get a Y cable that will bring two RCA outputs from my Preamp into the single RCA input on the REL?

Or is there another alternative?

Advice appreciated. (But please try not to tell me to just buy a second sub.)
hilde45

Showing 3 responses by imhififan

Or is there another alternative?
You can connect your preamp  second main out to a 
Stereo to mono signal converter
and connect one of the converter mono output to the REL 328 low level input. This converter utilizes an independent 1:1 ratio audio transformer for each channel, which also function as a ground loop isolator.

https://www.ebay.com/itm/MCM-CUSTOM-AUDIO-50-20795-Stereo-to-Mono-Signal-Converter-/164155969190?_tr...

An alternative is that I get a Y cable that will bring two RCA outputs from my Preamp into the single RCA input on the REL?
Unless there’s a resistor in series to the preamp outputs, using a ’Y’ cable that bring two RCA outputs from your Preamp into the single RCA input on the REL is a big no no!
almarg already explained to you:
connect a y-adapter to the two tape out connectors, to create a mono signal for the sub by shorting the signals on the two tape out connectors together, you would also be shorting the signals on the main out connectors together. Thus an identical summed-to-mono signal would be provided to both monoblocks.
Don’t do that!!!
REL’s response: "We would recommend connecting low level from your preamp to the R328 as the safest connection for your current setup. As long as it’s safe to use a Y splitter out of the QS preamp, this will be fine for going into the single input on the sub."
I can’t understand why REL gave you such advise.
Regarding your recent question about the device suggested by @imhififan , when I looked at the links he provided what particularly gave me a fair amount of confidence was the statement on the packaging that can be seen in one of the photos, that "it provides mono output while retaining L/R input isolation." I interpreted that to mean that the left input and the right input are isolated from each other.
Thanks @almarg for clarify, the MCM converter is utilizes an independent 1:1 ratio audio transformer for EACH channel, so the left and right inputs are isolated from each other.