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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.)
128x128hilde45
hilde45's avatar
hilde45 OP
4,974 posts
 
@ieales I appreciate your input and will look at the links. There are now a lot of different opinions out there. The amp mfr says it’s fine. REL prefers high level to their own sub if there are two subs. Otherwise, they say low level but have no answer as to how to sum the stereo signal to mono. Others on this thread say both.

Can you clarify what you meant by "Their" when you said:

you should NEVER use the high level output. Especially on a tube amp. Their use is strictly lofi.
Thanks.
daveyf's avatar
daveyf
2,871 posts
 
@ieales   Cannot use the high level with a tube amp?...go to my system page and take a look at how this can be done...with no issues.
almarg's avatar
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almarg
9,670 posts
 
Ian ( @ieales ), thanks for the references.  The OP's amps have a specified damping factor of 20, which at least in theory corresponds to an output impedance of around 0.4 ohms for their 8 ohm tap.  That impedance of course being well below average for a tube amp, and almost approaching solid state territory.  And the Salk speakers he has or will soon have are specified as 8 ohms nominal, and I suspect don't go much below that value at any audible frequency.

Wouldn't such a pairing significantly ameliorate the effects you refer to in the section entitled "Connection" of your paper shown at the second of the three links you provided?  I recognize, of course, that those effects would still be present to some degree.

Best regards,
-- Al

lalitk's avatar
lalitk
5,437 posts
 
“you should NEVER use the high level output. Especially on a tube amp.”

I am not sure the basis of this statement. I am using a pair of REL subs via its high level input with tube mono amps (8W SET’s). I hear no compromises in bass production or lack there off. 
ieales's avatar
ieales
1,201 posts
 
@daveyf
which system page? please post impulse and phase plots. I had a look. I find the Sonus intolerable. The low end is just awful in every system I’ve heard. [I’ve never owned a ported system]. I didn’t care for Nordost speaker cables in any demo.

@almarg
The QS have low output impedance, but if one looks at response into a real load, it is nowhere near flat.

Additionally, current drives the loudspeaker and voltage drives the sub. For any non purely resistive load I & V differ by an ever changing phase angle. Hence, a sub driven from the LS out can N E V E R be time correct with the mains.

@lalitk
I hear no compromises in bass production or lack there off.
I'm sure there is plenty of level.

I must admit that Time Coherence is my grail and systems without it are uninteresting. IMO, frequency response is, and always has been, overrated.

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