More powerful amp for top or bottom?

Both Amps are Wyred4Sound; the pre is a BAT VK30SE

I took a look at the specs on those components.

Both W4S amps have the same gain, so that issue (no. 2 in my previous post) is ok.

Their input impedances are 60K, so two of them in parallel would have a combined input impedance of 30K, which is comfortably high in relation to the 300 ohm nominal output impedance of the BAT (even if the output impedance were to rise to 3000 ohms or so at deep bass frequencies, which is not uncommon among tube preamps). So you could split either the rca or xlr outputs using y-adapter cables (xlr y-adapters are available), to drive the two amps.

Both amps have extremely low output impedance, so item no. 5 in my previous post is a non-issue.

Because of the similarity between the amps, no. 3 in my previous post would seem unlikely to be an issue.

The cable capacitance issue can be avoided by using low capacitance cables, and/or avoiding long runs.

So the only potential issue, as I see it, is how much of the 570W amp's power you will be able to utilize. I would suggest contacting W4S and asking them if they can tell you what the internal voltage rails are for the two amps. If the numbers are not too different, I think you'll be fine.

Regards,
-- Al

Good work Al.

http://sound.westhost.com/bi-amp.htm

Depends on crossover frequency how much power you need per amplifier above / below the crossover point.....

Al,
Educate me, please. I thought that many amps increase in output as a logarithmic function, not linear. As input power from the pre is "amplified" that each step in volume is not linear but a function of the amps total output power? ie turning a pre-amp up 1/2 way will not necessarily utilize 1/2 of the amplifier's output capability.
Even if we look at this as a linear function, 1/2 volume on the pre amp would be 1/2 of the amps output capability. Therefor, 1/2 volume for a 100 watt amp will be 50 watts and 1/2 volume on a 240 watt amp is 120 watts. That's about a 4-5 db imbalance?
Thanks (no I'm not an engineer and yes, that's part of my problem...)

Hi Elevick,

Those are good questions.

The volume control on a preamp or integrated amp is indeed not linear, and will approximate to some degree being logarithmic, which is necessary because our hearing mechanisms are to some approximation logarithmic.

Power amplifier gain, as you realize, is often expressed in terms of db, which is a logarithmic scale. However, what the amp is really doing is generating an output voltage that is directly proportional to the input voltage, meaning that the input voltage is simply multiplied by some numerical constant, and providing the capability of supplying the amount of current that the speaker's low impedance will draw at that output voltage.

In this case the W4S amps have a gain of 27db, which corresponds to a voltage gain of about 22.4 times, based on the 20(log(V1/V2)) relation between db and the ratio of two voltages. So what the amp is doing, within the limits of the maximum output voltage, current, and power that it can handle, is generating an output voltage that is 22.4 times greater than the input voltage, at any instant of time.

Viewed in that manner, I think you will see that if some other amplifier had a voltage gain of say 30 times, and we provide the input to it through a resistive divider which in conjunction with the amp's input impedance attenuates the signal by a factor of 22.4/30 = 0.75, then the two amps will be gain matched for any signal amplitude and preamp volume control setting that is within their capability.

Best regards,
-- Al