I have been considering the 990 with a 7125 or a 755 and the new 770/790 when it comes out. What I thought I would do is feed two channels to each of the front mains, and use two chanels for the second zone.

My question is if both the xlr and the rca outputs are hot? As an example, could I run the right front xlr to one channel to power the bass of an Axiom M80 and then run the RCA right front output to another channel to power the mid/high input to the same speaker? Another alternative would be to split the RCA outputs into two amp channels.

Is this even worth the added expense of another amplifier?

I'm not aware of any pre-amps that don't have the RCA and XLR outputs "hot" at the same time.

Cheers,

Yes, it is worth the expense. You are talking about sending the full range to each of the amps, but the bass amp will take the heavy work of low freqs and a lot of the distortion will not be reproduced as your passive xover will limit it. The mid/amp on the other hand will not have to contend with much hard work, and so the more critical high freqs will be clearer (amp will stay in A mode longer, as less current draw) Even better, use a active xover after the 990, and befroe the amps. A Behringer has balanced ins and outs, and is VERY inexpensive...
I started with the Behringer, and now use DEQX 2.6

It depends on who you ask, what speakers you are driving, what amps you are using to drive them, and your own personal preferences, but there are a few thoughts that occur to me. The arrangement you are considering is passive bi-amping, using either a 125W amp (Model 7125) or 200W amp (Model 755 or its successor) to drive the highs and a 200W amp (Model 770 or its successor) or 300W amp (Model 790) to drive the lows. Passive biamping's main benefit is typically cited as being additional power - it is a way to give very inefficient speakers a lot of power or to make good use of lower power amps paired up to offer the same amount of power as a single larger amp. I have a hard time picturing a speaker that would need more power than 200W (although some do exist), and more than 300W would be even less likely. It is a very large financial investment that I fear would yield very little benefit, especially with any rather typical home theater speaker. I would tend to recommend going with the 770 or its successor without bi-amping, or if you have particularly inefficient speakers that need a great deal of power hold out for the 790.

As for the balanced XLR and unbalanced RCA outputs on the 990, I believe that both are active simultaneously. I do not know if there would be level differences between the two when used in a bi-amp arrangement (in some cases, the gain on a balanced circuit will differ by as much as 4dB from an unbalanced circuit). The Outlaws should be able to give you a definitive answer if you do decide to pursue bi-amping, however.

My $0.02...

Active biamping is great. In essence, this is what bass management does, that is, 'steer' all the low frequency stuff to a driver that can handle it (i.e. the subwoofer), and remove it (PRIOR to amplification) from the other speakers. Granted, how true this statement is depends on whether the pre/pro is set to allow full range to the sats, or use the crossovers. If 'steering' the low frequency away from the sat speakers, then this allows the sub and its amp to focus only on the lows, and the sats' amplifiers get everything above the crossover frequency.

An equally important benefit is that the amps driving the rest of the speakers are not 'tasked' with reproducing the bass information. In essence this can drastically lower the power demands from each amplifier and in the process, helps prevent clipping as the amplifiers are not being asked to reproduce the low frequencies. Indeed, this is one of the benefits of using the active crossovers / bass management in a pre-pro.

Also, because the satellite speakers are now not reproducing low bass energy, this tends to lower distortion from them (because their cone excursion is less as there is very little low frequency content for them to try and reproduce). Thus, in general, the satellite drivers undergo less excursion related to low frequencies, so there should be lower distortion than a passive bi-amplified system. Indeed, this is why sound reinforcement (concert systems) are done this way, only in that type of setting, 3 or 4 way crossovers are quite common (and almost always, active rather than passive crossover networks).

Now, you could conceivably take the line out (whether RCA or XLR) and feed that to a two-way active crossover (but you'll need a dedicated crossover per channel) if you wanted to bi-amplify your speakers, but you'd then need amplifiers for each tweeter. In essence, using bass management with downstream two-way active crossovers would amount to a tri-amplified system.

However, when this is done in pro-audio, almost always the passive crossover is completley absent, that is, the amplifier is directly connected to the driver as it is understood that the crossovers will be done at line-level (i.e. ahead of amplifiers), making the passive crossover redundant / superfluous. So, proceeding as such, there could be some interaction between the crossovers and your bi-amped feeds....although one could easily bypass the internal passive crossover networks (depending on one's comfort level with doing that sort of thing) in a speaker and in effect, be driving the drivers driectly from the amplifiers that are downstream of the active crossovers.

Mark

Hi,

Another question to bi-amping; I've got a pair of Gallo Ref 3's on order, which are bi-ampable, with another amp to drive the 22Hz-50kHz bass driver.

Assuming I have a 5.1 setup, can I use the 'extra' 2 channels to bi-amp the 2 front mains? It would require the ability to filer a low freqs (40-180kHz). Basically, it would duplicate the function of Gallo\'s SA Amp

I'm not sure if this makes sense, or if I'm explaning it correctly. It be great if the 990 was flexible enough to use additional channels to driver the bass drivers of these speakers

You can certainly split the pre-amp output and connect to unused channels of the amp to bi-amp. The signal will be full range to both amps (although the 990's bass management will subtract some information away for the subwoofer, ranging anywhere from 40Hz to 150Hz or so depending on where you set the crossover for the mains). If you wanted to have a low-pass filter of some sort on the channels driving the woofers, you would need something in addition to the splitter - an option that occurs to me is Outlaw's ICBM. You could connect the left and right pre-amp outputs to the ICBM, set it for stereo subs, and use the left and right subwoofer outputs to feed the woofer amp channels while using the left and right outputs to drive th eother amp channels. The standard ICBM has a max crossover point of 120Hz, which wouldn't quite work if you were looking to have a 180Hz crossover, but the Magnepan edition of the ICBM uses higher crossover points (I believe it ranges from 80Hz to 240Hz in 40Hz increments).

Thanks for the responses. I am confused why a separate cross-over would be needed. If I were to split the rca output to two different amplifier channels, and then run one to the high input and the other to the low input on the speakers, then as Gonk said, I would have two full range feeds (except what is sent to the subwoofer), though obviously the internal speaker crossover would use what portion of the signal is necessary. It seems that if done with a 770, I would have 600 usable watts (to 4 ohm speakers) rather than three hundred, which would drive the speaker with far less resistance.

Other than the likelihood that the end result is no better than simply connecing the speaker to a 600 watt amp, or bi-wiring (which I know is different), what am I missing?

Bruce why can't you just run the subwoofer output to the spare channels and on to the Ref 3 woofers? That is basically what I do with my Rocket RS1000s which have a built in amp and woofer.

The separate crossover isn't needed - as you have noted, you can always rely on the crossovers built into the speaker. However, active bi-amping (which involves eliminating crossovers at the speaker and placing them upstream of the amps) is generally considered to be a more beneficial form of bi-amping. Passive bi-amping (the arrangement that you describe in your post, with the speaker's internal crossovers still being used) basically only allows you to feed the speaker more power.

I can think of very few speakers that would be likely to benefit from a change in power output from 300W (at 4ohms) to 600W (also at 4ohms), which is why I initially suggested that this arrangement might not yield a detectable benefit. However, I don't know what speakers you have, so I could be wrong. Could I ask what speakers you are using?

Here is the thing: A 200 watt amp sounds better when operated at or below it's "class A threshold" which I believe is about 15 watts for the 755. I need to everything I can to keep the power low, and signal clean. Hence, I activly bi-amp. Passive yield benifits as well, the mid/treble amp doesn't get "pulled down" by heavy bass hits. My advice? Simply try it in stereo only mode, and leave the rears out of it temporally. Listen to complex music in single amp wiring, at a pretty agresive level, then with your extra cables at the ready, hook up the passive bi-amp connections and extra amps (maybe using a outlaw "Y" connector) Listen AT THE SAME volume (maybe be sure with a SPL meter)You will hear better defined bass and clearer cleaner midrange/highs. If I am wrong, no loss except for maybe the "y" connectors...

Oh, I forgot. A good many speakers that have bi-amping connections (as opposed to bi-wire connections) have jumpers that are in place for single amping, and removed for bi-amping. When they are removed, the woofer is electrically isolated from the mid/high connections. Hence, the amp connected to the woofer can impart no distortion to the midrange. The inductor and such is still inplace, so the range hitting the speaker is still limited to what it can handle. The same is true of the midhigh, the half of the xover that limits lows from reaching the mids still protects it, but no load whatsoever from the woofer will be seen by the mid amp. Of course, the bass signal hits the front end, but if there is no low freq load, it lightens the work it need to do and limits distortion...