How connect single subwoofer with 2 monoblocks

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hilde45

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How connect single subwoofer with 2 monoblocks
« on: 13 Apr 2020, 02:47 pm »
Hi all,
I'm trying to figure out how to connect my REL 328 sub to the QS Preamp or Amp. The sub can connect to stereo amps in a few ways:

(a) high-level (a "Speakon" cable with three strands — Red-to-Right+, Yellow-to-Left+, Black-to-Right-negative);
(b) via a single low-level RCA-RCA cable;
(c) via single LFE RCA cable (but this is ruled out because I want to connect for audio listening not home theater). 

The question regards how best to connect REL to QS monoblocks or QS preamp. Here's what I've learned:

(a) High level. REL says DON'T connect ALL 3 high level wires to speaker terminals (as one would with a stereo amp) because with monoblocks it will create a hum. However, if I do want to connect the two positive wires and ground the third elsewhere, where should I do that? On the preamp chassis? Some other way or place?

(b) Low level. If I try to connect the REL to the Preamp Out, I will need a Y cord to combine the Preamp stereo out to a mono input on the REL. But I've heard this will cause the monoblocks to become monaural, too. (Is that true?)

Comments on the above ideas? Other suggestions?

Thank you!

rollo

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Re: How connect single subwoofer with 2 monoblocks
« Reply #1 on: 13 Apr 2020, 03:39 pm »
  Does your preamp have [ 2 ] outputs ? If so use IC to sub and IC to amps.


charles

hilde45

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Re: How connect single subwoofer with 2 monoblocks
« Reply #2 on: 13 Apr 2020, 03:48 pm »
It does have two outputs. One already goes to Monoblocks and the other could go to sub, as you suggest.

As I mentioned this possibility in my OP, I said this: "I will need a Y cord to combine the Preamp stereo out to a mono input on the REL. But I've heard this will cause the monoblocks to become monaural, too. (Is that true?)"

Do you have a specific comment about that possibility?  Thank you.

sunnydaze

Re: How connect single subwoofer with 2 monoblocks
« Reply #3 on: 13 Apr 2020, 03:53 pm »

snip....

(b) Low level. If I try to connect the REL to the Preamp Out, I will need a Y cord to combine the Preamp stereo out to a mono input on the REL. But I've heard this will cause the monoblocks to become monaural, too. (Is that true?)

snip...


Why would connecting your sub to a L / R pair of preamp outputs have any effect whatsoever on your main amps?    :scratch:

I'm assuming your pre has 2 pair of variable outputs:  one pair to the amps, one pair to the sub.

Phil A


sunnydaze

Re: How connect single subwoofer with 2 monoblocks
« Reply #5 on: 13 Apr 2020, 04:14 pm »
The first 20 seconds this video says you cannot use high level to connect a single sub to mono amps.  So your option (a) is eliminated.

https://relsupport.zendesk.com/hc/en-us/articles/115004649048-Stereo-Subs-Connection-Method

So you are left with only option (b):

https://relsupport.zendesk.com/hc/en-us/articles/115004649288-How-to-connect-your-REL-via-Low-Level-

If your sub has a pair of RCA inputs, simply connect a pair of IC from your preamp.  If your preamp only has one pair RCA outputs, you need to buy splitters to send signal to both main amps and sub.

If your sub has a single RCA input,  your need buy a "reverse splitter"  (dunno the technical term) that combines the L /R preamp output into into a single input into the sub.


hilde45

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Re: How connect single subwoofer with 2 monoblocks
« Reply #6 on: 13 Apr 2020, 04:16 pm »
Thanks for your replies.
Phil A. None of the REL videos or posts address this issue precisely enough. I've reviewed them.

Sunny daze. There is some debate about (a) -- if it's grounded on the chassis to avoid hum.
Re: (b) Good point about the variable. I need to check to see how it was wired, exactly. Just to review:

My question: "So, before I ordered the preamp, I had Mike wire the "Tape Out" as a *second* main out. Right now, the preamp's MAIN OUT goes to each monoblock and the other (TAPE OUT -- now a second main out) is free. 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?"

Answer I received: "Don’t do that! It would result in the main speakers reproducing mono. And although I doubt that it would happen in this particular case, with some preamps doing that might even result in damage, eventually if not sooner, since you would be shorting the preamp’s outputs for the two channels together. Presumably the change that was made disconnected the two tape out connectors from the internal circuit points to which they are ordinarily connected, and connected them instead to the main out connectors (or to corresponding internal circuit points). So if you were to 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.

sunnydaze

Re: How connect single subwoofer with 2 monoblocks
« Reply #7 on: 13 Apr 2020, 04:32 pm »
So it sounds like your sub has only a single RCA input?

If so,  I'm surely not technical enough to know if combining your  2nd set of variable outputs (the converted TAPE OUTS) and running them into a single sub RCA input results in a mono signal at your main amps.

If so, seems to me all you can do is:

(1) buy splitters to turn your preamp's main RCA outputs into 2 pair

(2)  run one pair into your mono amps the normal way

(3)  on the other pair,  get a "reverse splitter"  that combines the L and R into
one, and run it into the sub's single RCA input.

CAVEAT:  unless doing (3) will also create a mono signal at main amps.   Too confusing for me!!

A bit cumbersome, but there you have it.  If there's another way, I'm not aware of it.

sunnydaze

Re: How connect single subwoofer with 2 monoblocks
« Reply #8 on: 13 Apr 2020, 04:38 pm »
 The other solution is to:

(1)  get another identical sub.

(2)  use your preamp variable TAPE OUTS to drive the sub pair:
run the R i/c to one sub, and the L i/c to the other sub.

Need to research it to be sure, but I do believe that with a sub pair you can now run them high level with your mono amps.  Dual subs simplify everything, and yields better sound in the process.

Alternatively, if you prefer a single sub, sell your current one and buy one with a pair of RCA inputs.  Problem solved.

opnly bafld

Re: How connect single subwoofer with 2 monoblocks
« Reply #9 on: 13 Apr 2020, 04:40 pm »
Buy 2 REL subs at xxxx vs 1 at xxxx for stereo.
More better.  :thumb:

hilde45

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Re: How connect single subwoofer with 2 monoblocks
« Reply #10 on: 13 Apr 2020, 04:43 pm »
Thanks for the advice.
The whole issue derives from this REL having 1 RCA input and the fact of the monoblocks.
The possibility (not suggested by you folks!) that I cannot connect very good gear seems ludicrous. Surely there is a way.
Buying a second sub is not out of the question, but I'm trying to solve this problem, now.
I appreciate the suggestions.

mikeeastman

Re: How connect single subwoofer with 2 monoblocks
« Reply #11 on: 13 Apr 2020, 04:47 pm »
I have a situation were I have an all in one with no outs for the sub. I use a Jensen Iso-Max that connects to the amp speaker binding posts and gives you a XRL or RCA out, depending on te model, you might look into one for your situation. You would still need the y-splitter.

hilde45

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Re: How connect single subwoofer with 2 monoblocks
« Reply #12 on: 13 Apr 2020, 04:52 pm »
Thanks. Good lead!

opnly bafld

Re: How connect single subwoofer with 2 monoblocks
« Reply #13 on: 13 Apr 2020, 06:14 pm »



Stereo to mono adapter internet search.

hilde45

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Re: How connect single subwoofer with 2 monoblocks
« Reply #14 on: 13 Apr 2020, 06:20 pm »
Thanks. Need to be sure that such a cable doesn't collapse the stereo field to mono.

opnly bafld

Re: How connect single subwoofer with 2 monoblocks
« Reply #15 on: 13 Apr 2020, 06:25 pm »
Not a cable; a box with 2 rca in 1 rca out.

hilde45

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opnly bafld

Re: How connect single subwoofer with 2 monoblocks
« Reply #17 on: 13 Apr 2020, 06:36 pm »
Yes, something like that.

sunnydaze

Re: How connect single subwoofer with 2 monoblocks
« Reply #18 on: 13 Apr 2020, 09:03 pm »
Confusion and conflicting opinions abound on this subject.   Here's a thread that encapsulates it perfectly -- it looks like there is no black and white answer:

https://forum.audiogon.com/discussions/stereo-sub-out-to-mono-is-it-safe

opnly bafld

Re: How connect single subwoofer with 2 monoblocks
« Reply #19 on: 13 Apr 2020, 09:13 pm »
Confusion and conflicting opinions abound on this subject.   Here's a thread that encapsulates it perfectly -- it looks like there is no black and white answer:

https://forum.audiogon.com/discussions/stereo-sub-out-to-mono-is-it-safe

If you think there is confusion why don't you try it and tell us how it works out.  :wink:

The OP in that thread has an integrated with outputs labeled "sub".

 :green: