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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.)
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Showing 1 response by hman7

hman7's avatar
hman7
1 posts
 

I have a REL S/812 and two PrimaLuna EVO 400's as mono blocks.

this is what I received from REL

Thank you for contacting us, and for choosing a REL Acoustics subwoofer for your home audio system. While some older REL designs did allow for a single subwoofer to simultaneously be connected High Level to two monoblock power amplifiers at the same time, with all current REL models including the S/812 a single subwoofer should not be connected High Level to two monoblocks at the same time. Doing so will in most cases result in a significant ground loop hum which can be near impossible to eliminate, and in a worst-case-scenario can result in damage to the subwoofer and/or the monoblock amplifiers. 
 
When using a single REL subwoofer in a system that features monoblock power amplifiers, the best option will be to connect it to open outputs on your preamp using the Low Level input. This will allow the subwoofer to safely draw signal from both the left and right output channels, and since the Low Level input feeds through the same filter circuit as the High Level input you will still have full control over the S/812's Crossover dial for tuning it's output to blend with your main loudspeakers. 
 
In this system it is also possible to connect using the High Level input to one of either the right channel or left channel monoblock amplifier. This will of course result in the subwoofer only receiving either left channel or right channel signal, though since sub-bass content in many popular recordings is centered in the stereo mix, meaning that it is common between the right and left channels, it will still be possible to achieve a seamless blend with your main loudspeakers when connecting in this way. When connecting in this way to the Primaluna EVO400, please refer to the following instructions:

  • Twist together the red and yellow wires of the subwoofer's High Level cable, and connect to the 8 ohm positive output terminal on one of the two monoblock amplifiers.
  • Connect the black wire of the High Level cable to the negative output terminal on the same monoblock amplifier. 

 
I hope that this helps, but feel free to let me know if you have any additional questions or concerns. 

 

 

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