Subwoofer connection to older tube amp

I need to connect my Dominator 8 Sub to an Audio Research D-90 Amp and SP-12 Pre. The amp outputs only allow left and right bare wire speaker connections for different ohm ratings and I'll use the 8 ohm for main speakers.

Like most subs I'm afforded 2 pair of Left & Right Speaker Level inputs and 1 pair L&R Line(RCA plug) inputs and 1 pair L&R Line outputs.

Where would I hook the L/R from the amp to the sub? I want to use the set-up mostly for music but also for movies/DVD's.
If you have bare wire (terminated) for the sub you'd connect them to the same terminals on the amp.
So just connect the sub wires to the same amp terminals as the main speaker wires?
Yup. That's it.
Unless you have an extra set of line-outs from your pre-amp. Then you can run RCA or XLR cables from the extra main/line outs from the pre to the line in on the sub.
Thanks guys. Didn't think I could double the speaker wires on the same inputs but makes sense now. Appreciate your help.
Use the sub amp and save the power from your tube amp for speakers only. Your tube amp might not like the load if you hook up speaker wires to speakers and sub. You can run line level to the sub and then line level out of the sub to your amps.

The other way to do it would be to use a Y spliter cable coming out of your pre-amp. Run line level to the sub and another to the D-90 amp. you can also buy rca splitters that are machined out of a block. Audioquest makes one.
As explained to me by the main tech at HSU, the builder of my sub, the second set of speaker cables going to your sub from the main speaker terminals aren't drawing any appreciable power, they're just picking up frequency and amplitude information to be amplified by the amp in the sub. He said the gauge of the cables going to the sub doesn't even need to be the same as your main speaker cables since they're carrying very little power.
Thanks Sfar. If I can just run parallel wires off the same amp out connector that sounds easiest.

I appreciate Steuspeeds directions for using the line level outputs but as long as there isn't a real power drain on the D-90 and the sub amp is being used I'll do the joint speaker wire set-up.
That is how the high level inputs on a car stereo amp work for head units with no pre-amp out. It should work ok then. The down side is that the signal is amplified by the D90, un-amplified and re-amplified by the sub amp. This is likley to produce muddy bass. For best fidelity use direct rca line level connections with splitters like the Audioquest.
OK, but I'm still not sure what line level connections I have on the pre or the amp. The pre may have those but the amp really just has screw posts for speaker outs at different ohm levels. The only RCA style inputs is the Main for the pre input.

The sub has RCA line levels connections but not sure about these older tube electronics.
Sorry if this explanation is simplistic but I'm not sure where your confusion is.

Your power amp has two kinds of connections, both of them inputs. The first is the right and left inputs coming from the outputs of the preamp. Those are the RCA connectors on the back of the amp connected to RCA connectors on the back of the preamp. Those are line level - output from the preamp to input on the amp. There aren't any line-level outputs on the amp, only line-level inputs. The only output from the power amp is high-level, also called speaker-level.

The second kind of connectors on the amp are the speaker posts. Those are the speaker-level outputs that go - obviously - to your speakers.

The preamp can have a couple of kinds of outputs, the one kind every preamp has is a pair of line-level outputs controlled by the volume knob, like the ones going to your amp. You might also have another pair that aren't controlled by the volume knob, intended to go to a recording device and usually labeled "Tape out" or something like that. That's no use to you in this situation, even if you have them, since you want the signal going to the subwoofer to be controlled by the volume knob on the preamp.

So, you have two choices. First option is to use speaker cable to connect between the speaker terminals on your amp and the speaker-level inputs on the sub.

Second option is to split the output from the RCA connector outputs on the preamp using a 'splitter' as Steuspeed suggests and use two interconnects, one pair going from the splitter to the RCA inputs on the amp and the other pair going from the splitter to the line-level inputs on the subwoofer.

Some preamps have two sets of line-level outputs on the preamp but most don't. I'm assuming here that yours is one that doesn't.

The option I was recommending was option 1, the option Steuspeed was recommending was option 2. Either of them will work, which works better for you depends on your gear and what sounds best to you.

Sorry if this confuses things further. If it still doesn't make sense, please describe in some detail the connections you have on the back of your preamp.
Thanks again Sfar. My pre-amp is basically as you state. It has the main line level outputs(RCA) for the amp plus the RCA style tape output. So your saying that I can't use the "tape out", that I would have to split off the main out with one set of connectors going to the amp and the other to the sub?

I use a pretty high-end output cable between the amp and pre so I'd have to use a splitter thats a little better than Radio Shack quality to not diminish the connection to my amp.

I do want to use the amp in the sub since its 1000 watts and designed for it. If I just double the speaker wire connections off the amp- one set to main speakers and the other set to sub, it seems it would defeat the design of the sub and may overload the amp.
Right, you can't use the 'tape out' connections because they're not controlled by the volume control on the preamp, meaning the volume coming from the sub wouldn't change as you adjust the volume to your main speakers.

If you do want to split the preamp output you can use one of the devices Steuspeed recommended. He suggested one from Audioquest and there's another from Monster. Click here to see what the one from Monster looks like. Both it and the Audioquest version are solid connectors, no wire involved.

You shouldn't worry about using the speaker wire connection method, though. The subwoofer amp won't be pulling any substantial power from your main amp and won't overload it at all. That connection method is the one recommended by both REL and HSU, makers of some of the better subs out there. You should definitely do what you're most comfortable with, however, it's your gear.
So if I just go with the doubling of the wires off the same 8 ohm speaker output directly from the amp I'll be fine? That would be easiest and I wouldn't have to go out and buy more connectors.
Also, do I need to run left and right wires or just a single? Right now I'm using an A/V receiver that has the single RCA Sub output and its connected to the left input on the sub. Now I want to switch back to using my Audio Reserch gear. Do I need L&R or just go with one speaker wire off the ARC amp to say the left speaker sub input?
Ok, I called Audio Research and talked with Leonard in the service department. I think he's been there forever and remember speaking with him maybe 15 years ago when I first got this equipment.

Anyway, he basically said to go ahead and hook-up the dual speakerwire set-up. He did confirm that the "Tape Out" on the pre-amp would not provide any volume. Said to double the wire L&R for both the main speakers and the sub.

There is a warning in the Sub manual saying the amp must be common grounded for this connection, but Leonard said that's fine and not an issue. So I'm going with the dual speakerwire config and let you know how it goes.
Well, everything is hooked-up as described above and no probs, sounds great.

Thanks for the input and help.

That's great, congratulations. Now you can take your time adjusting the output, crossover and phase settings to get it to sound best with your system. You'll probably find that what works really well for one recording isn't ideal for another and it takes some going back and forth to find the setup that's the best compromise.
Right on. Thanks again for your help.
I know it is and old post but I really want to know: does this dual speaker wire to sub work for tube amps?
Davidrb - Yes, it will work fine with a tube amp. I used that setup for a couple of years with and AES/Cary Superamp. The amp has five-way binding posts and I used spade connectors on the cables to the speakers and bananas plugged into the same binding posts for the cables to the sub.
It sounds great. Are the cables the same AWG? Or shall I use thiner cable for the sub?
According to the tech at HSU I talked with there is no reason to use the same gauge cable for the sub since all it is carrying to the sub is the frequency and amplitude information which the sub then amplifies on its own. He said, essentially, that using larger grade cable was a waste of money.

I used Canare 48s, I think, which was overkill, but I had bought a bulk lot of it from Markertek for another project and had it lying around. I've also used cables made from Cat5 network wiring, also because I had a spool of it, and it worked fine.
thanks for the input; I really appreciate it!
Hi, original poster here.
Is it possible to use the same SW for an HT system and a separate audio system?

Still have the ARC gear for audio and was thinking of using the same SW for the HT. Is it possible to connect a single SW RCA cable to my HT and continue using the dual wire method for the ARC amp/pre? The SW supports both single RCA input and dual speaker wire inputs.
Of course not having both systems on at the same time.

Jamesk58 - It would be a good idea for you to ask this question in a new post since the only ones who are seeing it now are those who answered your original question about the sub hookup.