Any risks with bi-amping?

[klitgt]

The attachment shows what I mean by Bi-Amping.
Am I right?
In this case the inputs of each poweramp will be connected to each other. Does this imply any risk of any kind to the poweramps? (Same make and model).

[quasi]

Looks ok to me.

What pre and power amps are you running?

Cheers

[sam9]

Maybe. Depoends at least in part on the parrallel input impedance of the two a amplifies. Cocievably the load could be too high for the pre. This is something that doesn't have a generic answer. I wouldn't trust datasheet data either. It's not that hard to measure input impedance using several frequencies (it's often frequency dependent).

By the way, the term "Bi-amping" as comonly used involves an active crossover between pre- and power- amp. The cross-over (assuming it is a LR type) is at the heart of the benefits. In your scheme, even if there is no problem you are likely to get only minor benefits for the cost of a second amplifier.

Please read the article on this topic to mbe found at http://sound.westhost.com. This explains pretty clearly why the XO is the at the heart of bi-amping benefits. In my view the additional amplifier is mainly an unavoidable expense and complication that the use the XO neccessitates. If you could build an active XO between the amp and the the speakers that would be better but it is not practicle with the current (pun intended) state of things.

[quasi]

Yep Sam9's answer is a lot better than my very detailed response.

I assumed that you would use the crossovers inside the speaker box, but that could be a mistake depending on the internal wiring configurations.

Sam9, most modern pre-amps will drive into 600 ohms, so I doubt the extra load will be a problem.

But you are quite right that an active crossover could be required.

Cheers

[sam9]

It also ocurred to me that if the scheme bypasses the internal XO, then each driver is subject to the full audio band. I don't know enough about drivers to be sure, but this arrangement may not be good for them. I would make inquiries, at least.

[klitgt]

Originally posted by sam9
It also ocurred to me that if the scheme bypasses the internal XO, then each driver is subject to the full audio band. I don't know enough about drivers to be sure, but this arrangement may not be good for them. I would make inquiries, at least.

It will not bypass the internal XO in the speakers. The poweramps each have 10Kohm input impedance and the pre (diy single Jfet single ended no feedback, see attachment) has 570 ohm output impedance.

I know that it is preferrable with an active XO but I was lucky to have the opportunity to buy two SiriuS DM100 poweramps (Today sold under the Gamut brand. Wonderful amp, see more on www.gamutaudio.com) for almost nothing.
Maybe one day I will add an active XO, just have to know the XO frequency of my B&W 803 matrix speakers.

[audiobomber]

Your proposed layout will work just fine. The system as you've drawn it is a passive horizontal bi-amp. You may also want to try a passive vertical bi-amp, where each power amp supplies one speaker (i.e. left channel of one amp drives the bass terminals on the left speaker, the right channel of the same amp drives the mid/tweeter terminals of the left speaker). Either way may sound a little better, depending on the system.

I expect you will find a noticeable improvement after passive bi-amping because of lower IM distortion and improved current delivery.

Originally posted by klitgt

Maybe one day I will add an active XO, just have to know the XO frequency of my B&W 803 matrix speakers.

Active bi-amping with an electronic crossover is not as simple as you might think. There's more to it than simply adding an off-the-shelf crossover. You still require a competent design to blend the drivers for good phase, baffle-step compensation, notch filters etc.

Let us know how your passive bi-amp works out.

[Cal Weldon]

While in essence that is biamping, it's not really what we think of. You need the XO to give you control over not only the XO frequency but the output to each amp and henceforth the speaker. There really isn't much advantage two have two amps driving the speakers without that control. Biamping is a wonderful thing if you have full control over the amps, not if you just do that.

If I had two amps and no XO, I would use each of the amps as a monoblock.

One of my outdoor systems uses a second preamp (Citation Seventeen used as a slave to the master) as an input control for the amp to the bass bins. That way I have a "sort of" biamping. Control over the cutoff frequency of the woofer because of the built in EQ and a volume control for balancing the woofers with the mains.

Cal