I am picking up an Outlaw Audio 950 processor and 770 (7 x 300 in 4 ohms) multichannel amp. I will be using VMPS Ribbon Monitor 40's as mains, VMPS LRC for center and VMPS ribbons & dipoles for surrounds. Right now, I would be bi-wiring the setup (L/R/C channels). I am using my setup for movies AND music.

Would it make that much of a difference if I purchased a stereo tube amp and bi-amped my front speakers, using the tube amp for just the highs and mids?

Being a musician, all I know about tube amps is from my guitar amp gear. I use Marshalls that have that el34 sound and Mesa/Boogies that have the 6L6/5881 sound.

Could I get away with just the SS Outlaw?

To check out specs on my speakers go here (http://www.vmpsaudio.com).

Thanks!

To do real bi-amping, you need to replace the internal passive crossover network in your speakers with an external electronic crossover. The problem with passive bi-amping like you propose is that both amps will be presented with full bandwidth. The tube amp in particular will still be required to reproduce the power-intensive bass frequencies, which could cause it to clip, potentially destroying the tweeter.

Usually, passive bi-amping requires two identical power amps for the low and high end drivers so that there are no power limitations and the gains are identical.

Personally, I think passive bi-amping is not worth the trouble (nor is bi-wiring).

You are absolutely right about the tube amp sound quality however. An alternative perhaps would be to use two stereo tube amps, with one channel of each driving the woofers and the other channel driving the tweeters. At least this would satisfy the equal gain problem. You might still run up against power limitataions however unless the tube amps have over approximately 40 watts, or unless your speakers are very efficient. I actually use a 5 watt tube amp for my tweeters in an active electronic crossover setup, but they are extremely efficient at 106db/watt.

sbcgroup1,

I have read about VMPS speakers for years, but I've never had a chance to listen to any.

I'd love to hear what you and fellow Outlaw's think about them.

Regards.

Jeff Mackwood

id agree that bi-amping is a waste, but disagree about bi-wiring. bi-wiring isn't going to dramatically improve your system, but its nice to have the highs and lows running along their own cables.

The flaw in that logic is that with bi-wiring, the signal travelling down each cable is identical. This is also true of passive bi-amping. The only way to make it so that different signals travel down each speaker cable is with an active system using an external electronic crossover to split the signal into a low frequency range and a high frequency range. These must of course be amplified by two seperate amplifiers. This is active bi-amping.

The only thing you "replace" with bi-wiring is that jumper that resides on the back of your speaker that shorts the two inputs to the passive crossover - the frequency split is done inside the speaker by this crossover network.

With bi-wiring, you are only moving that "jumper" from the back of the speaker system to the output terminals of the power amplifier - there is no electrical difference other than the effective gauge of the speaker cable is doubled. The same electrical result can be had by using a single run of larger gauge speaker cable.

At least with passive bi-amping the amplifier used for the high frequency section does not have to supply current in the low frequency range. An argument could at least be made for the benefit of this, although the audible benefit is questionalbe. This arrangement is also wasteful of resources, especially for the high frequency section.

Question: is it absolutely necessary to have two separate amplifiers? Can you do something like use a 4-channel amp (or 4 channels of a 5 channel amp) and get the same thing as a pair of stereos (or a quadrant of monos)? I've heard before that you want to have separate power supplies (or torroids at least) for this. How much of a difference does that make?

Ok, so there was more than one.

The amplifiers can be two channels of a 4 channel amp, or a 7 channel amp or whatever is most convenient. Any of these combinations will work, however completely seperate monoblock amps would totally avoid any power supply interaction. An amplifier with seperate power transformers per channel will act like monoblocks.

The next best thing would be to use two channels that share a common power transformer (and associated power supply components) for the left and right woofers, and two other channels that share a common power transformer for the left and right tweeters. This avoids interaction between the low frequency amps and the high frequency amps.

The world will not come to an end however if you use, say, an amplifier that has one power transformer for 4 channels. Unless you really crank the amplifier to the edge of clipping, the interaction will likely be below audibility.

There is another benefit to active bi-amping you should be aware of. You can use a much lower powered amplifier for the high frequency drivers since the power demands are nowhere near those of the low frequencies. If you have a 100 watt amplifier for the woofers, you could probably use something in the neighborhood of a 30-50 watt amp for the highs (depending on the crossover frequency - the lower it is, the more power you need in the high frequencies).

This also opens up the door for using something like a class "A" amplifier (or a class "A/B" amp that runs rather more into the "A" class than the "B" class) for the high frequencies. Tube amps are ideal for the highs because the power demands are less, the damping factor requirements are less, and class "A/B" tube amps by their nature run very rich bias - they run essentially class "A" up to a significant amount of their rated power. This makes these amps practically immune to crossover distortion. A single-ended triode tube amp would run pure class "A" and there would be no crossover distortion since there is no crossover, but this type of amp is probably not warranted unless you have extremely sensitive speakers like I do (or else you simply like SET amps).

Whether you go solid state or tubes for the highs, an active bi-amp system will sound worlds better than using speakers with passive crossovers.


[This message has been edited by soundhound (edited May 12, 2004).]

http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/audio/biwire/Page1.html
page three says there can be differences between bi-wiring and standard wiring.

also, feedback is generated by your speakers, so the high frequency feedback is going to go along its cables and low frequency feedback will go along its cables. i know for a fact that is the way my speakers are designed, with the feedback not going back through the crossover, but instead straight out the high and low frequency inputs.

"Tube amps are ideal for the highs"- id disagree with that as well, most tube amps are not "ideal" at all for anything other than door stops. the goal of a system should be accurate reproduction of a source, nothing more and nothing less.