Setting up dual subwoofers to a two channel amp.

Any advice would be really great:

I am currently running a dual-mono 300B SET amp into two back-loaded horn single driver speakers. A very simple setup. I have two subwoofers on the way... This complicates things. They will be active subs with either Keiga or Dayton SPA plate amps. I would like to use the high level in/out on each sub. The problem is that I am using one dual mono amp to feed two "stereo" (two in/out each) plate amps which will power each sub and then send the signal to the horns. Basically I am using these two subwoofer amps that are designed have two channels in and out, but I am only feeding one signal into each. Anyone know the proper way to set something like this up without bridging my main amp?

Also, how badly is the signal going to the main speakers going to be degraded by putting a sub in between?

Again, any help would be greatly appreciated. Thanks!
If I understand what you are asking. The subs do not need both channels. Send the left channel to the left sub and the right channel to the right sub. If each sub needs both inputs to have signal than use a Y cord at the input (its been a long time since I have seen a sub that needs both inputs with signal.)

Use the corresponding high freq output to continue to the amp for that channel.

As far as sound quality I can only speak to my results with my 300b based SET amp. So far I have not been able to find a crossover that is step back when feeding my 300b. I've tried the internal crossover of the sub, which is very poor sound quality. A seperate discrete SS unit, definitley better but than it sounds like a good SS amp instead of a SET amp. Lastly an integrated circuit based unit, which is suprisingly a little better then the discrete SS unit but still leaves me without the midrange magic and top to bottom cohesiveness of the SET amp.

Ofcourse YMMV.

I'm currently trying to find a SET based tube crossover that will get the job done in my system.
Thanks for the response. This makes sense. It doesn't sound like you are having a lot of luck with integrating your subs. Another option I am looking into is using Y cables at the sub from the main amp to the sub and the the Y cable continues to the full range speaker. Nothing from the high level out of the sub at all. I don't know what kind of load this will present to the amp, though.
Use an active pre-amp (SS is better than SET for bass response) with 2 RCA outputs to split the signal from the CD player/Media player/TT two ways - one direct to your 300B and then the Horns, 2nd using Y splitter further to drive each plate amp/subwoofer

My system is now PWD DAC II (has XLR and RCA both with active signal) - XLR to main preamp - 45 tube active and to my AN300 B monoblocks; RCA with splitter ie 2 lefts to left subwoofer bridged amp and 2 rights to right bridged subwoofer amp. Separate volume on PWD DAC, Tube Main Preamp, and adjustable X-over frequency and Volume on Subwoofer amps makes adjustment and blending seamless.
We need to clarify. When you say high level do you mean speaker level or preamp level?

From your last post it sounds like you are considering running the speaker hook ups on the amp to the "speaker level inputs" on the sub and then from that spot continuing on to the speaker. If so than the load presented to the amp is negligibly different as the "speaker level in" on the sub does not really load the amp per se.

If my description of your intended hook up is correct than what you will be doing is running your main speakers full range and augmenting the bass with your subs.

Is that your intention? If so I have an alternate hook up that is easier. Basically you use your existing speaker wire as you have it now and add a smaller gauge wire (as it will not be carrying any current) from the speaker hook ups on the amp going to the "speaker level in" on the back of the subs.

BTW, I am currently running my main speakers and SET full range and using my subs to augment everything below 80hz.
The only reason I am trying to add an electronic crossover is so that my SET does not have to work as hard when playing loud.

You are exactly right and articulated my previous statement much better than I could. One question: you mentioned that none of your bass augmentation has been satisfying. Including this method of adding the sub on top of the full range? Does this method we are talking about have a bad effect on the full range sound? Also, does adding a sub in the manner we are describing make the main amp work harder than if there were no subs at all? Thanks for your help in this!
In addition, would I be correct in describing the alternative method you mentioned as having two sets of wires running from one set of speaker posts on my SET? One set to the full rangers and one set to the speaker input of the sub amp?
"Does this method we are talking about have a bad effect on the full range sound?"

IMO, No if you can get it set up properly. Possible issues that may come up are; any overlap of the main speakers and subs as well as phase issues at the crossover point.

"Also, does adding a sub in the manner we are describing make the main amp work harder than if there were no subs at all?"

No. What I was talking about is in a true biamp set up (active crossover before the amps and sub's) I'd be removing the deep bass, below the crossover point, from the main amps. Simply put this would remove some of the demands on the amp since the bass requires much more power than the mids and highs do. My main speakers would also perform better as they would no longer be asked to do the deep bass.
The system would be able to play louder with less distortion. However in my case the quality of the mids and highs are negatively impacted by all of the active crossovers that I have tried so far. So I am running the SET amp and main speakers full range and using subs to augment the bass the main speakers can't do. After much "dialing in" the set up I am very happy.
This is all great info. Thanks so much!
I had a 2.2 set up with a single driver speaker, matching subs, and a 300b set amp. I ran direct from the amp to the main speaker then a jumper from the main speaker to the powered subs. I tried to dial in the subs as best as possible, but had nulls and phase issues at the crossover point that Jjrenman referred to.
I have since gotten away from horns and have a 2.2 set up using monitors and matching subs with a Dspeaker Antimode Dual Core 2.0. In reality you have an active system with each channel having it's own dedicated amp. Which will only need to provide enough power to run the driver to full excursion. Very smart for good sound!
I use my Dual Core as a preamp and dac with a transport to the internal dac. There are 2 digital inputs, optical SPDIF and USB, XLR and RCA analog inputs, with XLR and RCA outs.

So how will this work for you?

With the Dual Core you can measure the room and see where your horns begin to drop off and set your subs crossovers accordingly.
ie: My monitors drop off steeply at 100hz. I use a XLR to RCA cable from the XLR out to a single ended amp for the monitors. Then from the RCA outs to the subs amps dialed in at 100hz. I Then run a room correction at 150hz (or which ever point you want to choose up to 500hz) which fixes room nulls, and phase issues, as well as correcting the crossover point. The Dual Core's algorithm is so good that if you miss the proper crossover point by a few hz, it will make adjustments to bring the frequencies to proper alignment.

The Dual Core are around $1100.00 and will give you the great sub to speaker integration, as well as tone controls, equalizer, room measuring, tilt and house controls, up to 4 different profiles to save corrections in, asynchronous USB input, optical digital out, and support fron Dspeaker for future firm ware updates.

Oh by the way the Dual Core is responsible for the best bass and over all sound I have ever had in my room. ALSO *I'm not affiliated with Dspeaker in any way other than a very pleased customer.*

Dspeaker Dual Core
An interesting solution kelvin. I can do this with my Emm labs pre amp. Please forgive then ignorant question but I connect it to the volume out right? Rather than the line out? In order for the bass response to match the volume of the system as a whole?
Thanks for the advice, rodge but I think i am going to try to find as simple a solution as possible. As it is, my system is very simple and the components are as high quality I can get. Adding an additional component as complicated as the dual core you describe would not work for me. I am also using double backloaded horn full rangers and would prefer to stay with those and replacing my DAC/transport combination to anything other than the new playback designs stuff would be an automatic step back as what I have is the best I could find and afford.
Kelvinswy's hook up and mine are very similar. IMO, Going line level (main output on the preamp)instead of speaker level is better and will give you the added flexibility needed to match the horns to the subs.

I did not mention it earlier as you do not show that preamp in your "system".
Thanks jj! Yes. The Emm labs dcc2 is a pre amp in addition to being a DAC. This line out method is most likely the way I will go. It was my understanding that using high level speaker connections was the best way. But the line level seems to make the most sense as long as the preamp is up to snuff. Thanks for your help in this.

Go fourth and add deep bass!

Post again after set up and let us know how it worked out.
Absolutely! Thanks again to you and everyone for your help. It is very useful.