Bi-Amping RTA12C

That would require fairly extensive modifications for next to zero benefit if all you are going to do is run them off two channels of the same receiver.

P.S.

If you click the audiogon link in my signature, you can scroll down to look at the System Plan and see how a (very simple) active bi-amp set-up is implemented, and the Comments will make it more clear.

Look at the crossover schematic. (I am assuming that the RTA12B-rev is the 12C.)
http://www.polkaudio.com/forums/showthread.php?t=38755

You could isolate the tweeter circuitry pretty easily, by highjacking the white and blue lines before they get to the woofers, as you suggest. This leaves you running full range to the midwoofer, however, because it depends on the same crossover circuit as the tweeter. I'm not sure what would happen to the second woofer tuned to bass frequencies. One way to get around this is to use an active solution, as Geoff pointed out, but that has its own complications. The most obvious way to do it I can think of with a passive solution would be to build a second crossover board with a resistor in place of the tweeter, although that would be prohibitively expensive.

There are more technically inclined individuals here than myself. Maybe one of them will come along with a more elegant solution.

Man, I keep trying to type, and the Internet keeps crashing on me (fingers crossed this time)

Crashdot wrote: »

I am not sure I understand the difference, since it was my understanding that the Denon AVR-4306 has a discrete 130w power amplifier for every one of its 7 channels. The manual specifies that this is a Bi-amp configuration, so that is what I am operating from.

I'm looking at that on P.76 in the manual. What they have drawn there is a passive bi-amp. Using one amp channel to drive the Tweeter input, another channel to drive the woofer input. However, both amp channels are still responsible for reproducing the entire audio spectrum; the crossover inside the speaker is doing the frquency splitting.

I guess my question is this. How 'stiff' are each of these channels? I noticed on P.8 the usual caution about not running too many lower impedance speakers together off the amplifier section, which suggests to me that they may all have one common transformer. Do you know if this is correct? You'll have to forgive me, I admit I don't know that much about H-T receivers.

Crashdot wrote: »

From my understanding of how this receiver works, bi-wiring to this amp is not the same as with other amps where the same channel would just be sharing the load of the second set of connections.

Well, if you were to take Channel 1 only, and run two sets of speaker cables off of it - one set to the tweeter input terminals, and one set to the woofer terminals, that's bi-wiring. One channel, two sets of cables.

Crashdot wrote: »

For this reason, when I Bi-wired the RT55i, they sounded significantly better, presumably due to increased power available to each speaker section by dedicating entire amplifier sections to each.

So again, just to get our terminology straight, that's passive bi-amping. And there-in lies the advantage of this approach. But, it and bi-wiring are a couple of those funny things in audio. Some people seem to experience gains with it, other people call utter BS on it.

When my magnepans still had their passive networks, I tried bi-wiring. I can't honestly say there was any difference one way or the other. But, of course, that's a totally different speaker technology that the 55's. Things are bound to be different.

Crashdot wrote: »

There appear to be holes in the crossover that may accomodate binding posts, and otherwise, adding such a connection would be trivial. What I am curious about is what needs to be remain disconnected vs what stays connected. There are three wires that connect to the 12C crossover, two that are obvious from the speaker input, but one of them goes through one of the midrange drivers first. I am not sure why the passive bi-amping would not yield the same sonic benefits as they did with the RT55i.

It sounds like you pretty much have the connection figured out. Let me try to remember back 2 months ago.....

That black wire goes up from the binding posts through the connector, splits, goes through the 3.2mH, then back down through the conn. again via the blue wire, then to the 6501. So, to make them bi-wirable/passive bi-ampable....

Install another set of binding posts on the binding post cup, which will be the Low-Pass. You could run a wire from those Low-Pass binding posts that are now for the mid-bass drivers only (call it the "red" wire). The red could go up through the connector, which would require a 4-pole connector now, not a 3 (use the same Neutrik that I did, it's a 4-pole). Then right into the 3.2, and back to the 6501 via the blue. The original split of the black wire between the tweeter network and the 3.2 could be permanently cut now, but re-enabled w/ binding post jumpers if you wanted. The .61mH would have to be connected to those Low-Pass binding posts ONLY. So.....the + on the Low-Pass posts would be connected to the red wire and the .61. The black wire would still be the same, except it only goes to the tweeter network now and doesn't split off to the 3.2. Ya, that would work.

Sorry, just thinking out loud here. I better draw this before i confuse myself.

Crashdot wrote: »

I get the feeling that 130w is not sufficient to drive these speakers properly, and was hoping that bi-amping/bi-wiring might bring these speakers to life.

RTA12C's should not need anywhere near that, except, of course, on the most demanding transients.

Crashdot wrote: »

In addition, the crossovers in these 12C's were already fully upgraded with mills resistors, sonicap capacitors, and RD0194 tweeters by the previous owner, so I doubt there is anything I can do to further upgrade them aside from cabinet dampening, rings, and other physical modifications.

Outstanding!

They've probably gotten so many calls from people like us (modders) over the years that they go, "Oh God, NOT another one!":rolleyes: When I was starting to mod my Magnepans, I found something that really confused me in the panel hookup; the L and R speakers were opposite one another in their hookups and at the time I couldn't figure out why. So I called Mark Winey, son of the company's founder, who answered the call at tech. support. I told him what i was doing, and I could just sense it at the other end..... "Oh God, NOT another one!":rolleyes:

Well, we ended up having a pretty good conversation after a few minutes, with me feeling kind of emberrassed at having troubled him.

We figured out the answer to my question (with success). On a different occasion, I also had a couple great conversations with the (very knowledgable) person who used to write the set-up manuals for Maggie's back in the day, and he had some great suggestions, which also led to a successful implementation.

So see, sometimes it does work!