@Haywood310 After looking at the descriptions, specs, and/or manuals for the equipment you’ve listed, if (a)you are satisfied with the sound you are presently getting with the configuration you have described, and (b)assuming the specs on the equipment are reasonably accurate, and (c)the lengths of the cables between the preamp and the amps are not unusually long (for example, longer than 15 feet or so), I’m going to offer a radical suggestion for you to consider: A good course of action may very well be to do nothing :-) Just enjoy the configuration you have described.
It appears to me that the present configuration is fine with respect to all of the major technical pitfalls that can be encountered with a passive biamp configuration:
1) Gain matching: The BAT amp has a specified gain of 25 db. By providing it with a single-ended input, while there is no change in its gain per se (i.e., the relation between its output voltage and its input voltage), overall system gain is 6 db less than if you were providing it with a balanced pair of signals. In effect that reduces its gain to 19 db. While the gain spec provided in the manual for the Pass amp appears to have a typo (it says that its gain is "20 dB balanced, 20 or 26 dB balanced") after reading the text I’m fairly certain that its balanced input provides a gain of 20 db. So you only have a 1 db gain difference between the two signal paths. Room effects most likely make a good deal more of a difference than that.
And if you were to split the XLR outputs of the preamp and drive both amps with a balanced pair of signals you would be **introducing** a significant gain imbalance, that would require insertion of a suitable attenuator between the preamp and the BAT amp.
2) Impedance compatibility: As is often the case, the signal provided by the preamp to its RCA output for each channel is the same signal that is provided to pin 2 of the XLR connector for the corresponding channel. So that signal will be loaded by the input impedances of both amps. But the numbers are such that that is not a problem in this case.
3) Upper treble rolloff that in some cases may be caused by the interaction of preamp output impedance and the combined capacitances of the cables to both amps: Again, not a problem in this case assuming the cables are not unusually long.
4) Inability to utilize most of the power capability of the higher powered amp without clipping the lower powered amp: In this case the roughly 2:1 disparity in amplifier power capability **might** result in not being able to turn the volume control high enough to utilize perhaps 2 db or so of the power capability of the BAT amp, without driving the Pass amp into clipping, but that’s probably not a major issue. If you were passively biamping say a 400 watt amp with a 50 watt amp I would not say that.
5) Degradation of the common mode noise rejection that can be provided by the amp receiving the balanced signals, due to the differing load impedances presented to the two signals in the balanced signal pair: The output and input impedance numbers in this case suggest that is unlikely to be an issue.
Others have suggested changing the equipment. That’s of course something that can be considered, now or in the future, but if you are happy with the present equipment in the present configuration it seems to me that doing nothing is also a reasonable course of action.
Regards,
-- Al
