Miltiple amps for stereo Matrix 801's

When you say "two mono amps to each woofer," do you really mean one mono amp to each woofer?

Assuming that is the case, the connections can be made by using a pair of xlr y-adapters, such as these:

http://www.bhphotovideo.com/c/search?ci=4173&N=4289288134+4289360554

However, several things have to be kept in mind:

1)The gains of the amps have to be equal or very close to it, or else you will introduce a level mismatch between the woofers and the mid/hi's.

2)The preamp outputs will see a load impedance which is a considerably lower value than the input impedance of each amp. If the input impedances of all of the amps are the same, the preamp will see a load impedance equal to that value divided by 2. If they are not the same, the combined input impedance on each channel is the product (multiplication) of the two input impedances, divided by their sum. That number should be at least 10 times greater than the preamp output impedance, at the frequency at which the preamp output impedance is highest (which is usually 20Hz, especially in the case of a tube preamp). Otherwise a frequency response imbalance, such as deep bass attenuation, will probably result.

3)Low capacitance cables should be used, especially if the runs are long. The signal getting to EACH amp will be affected by the sum of the capacitances of the cables that are connected to BOTH amps. If that total capacitance is high, and if the preamp output impedance is high at high frequencies, upper treble rolloff will result.

Regards,
-- Al

Worldwide,

The two Bryston Powerpac models you mentioned fortunately have the same gain, either 23 or 29 db for their balanced input, as selected by a rear panel switch. That is indicated on page 8 of the manual.

I should have stated more explicitly that the reference to low capacitance cables and/or short cable lengths referred to the interconnects between preamp and amps, not to the speaker cables. The reason for that is that the sum of the capacitances of the two interconnects that are branched off via the y-adapter will form an RC low pass filter in conjunction with the preamp output impedance. The same thing occurs with any preamp to amp connection, but it becomes more critical using the y-adapter and two sets of cables because the capacitances of the two cables sum together, with respect to that effect.

What preamp will you be using? The lower its output impedance, the greater the cable length, and the cable capacitance per unit length, that can be tolerated. As a rough rule of thumb, with most cables and most preamps up to 10 or 15 feet would be ok.

Re bi-amping vs. using two higher powered monoblocks non-biamped, I can't say. Perhaps someone else who has experimented with biamping the Matrix 801's will comment.

Good luck!
-- Al

Specs don't appear to be available for the output impedance of the W4S DAC2.

If you biamp, regarding the cable capacitance issue I mentioned I would feel pretty confident that you'll be ok if the length of each interconnect is say 10 feet or less. Just avoid interconnects that have high capacitance, more than say 50 picofarads per foot (pf/ft).

However, the other impedance-related issue I mentioned may be a more significant concern. The Bryston amps have an input impedance at their balanced inputs of 20K ohms. Which means that if you were to connect each channel to two amps via y-adapters, the DAC2 outputs would see a load of 10K ohms. That is low enough to be a concern, and I would not want to opt for that approach without first somehow verifying that the DAC2's output impedance is less than 1K, and preferably well under 1K, at all frequencies.

Regards,
-- Al