Bi-amping Rules

Let's leave PA-systems out of the discussion. In them you want efficiency and the most bang for the buck at the least weight to haul around. You also have a brain behind the console to tweak the sound as he pleases and the music is produced rather than reproduced so there is no original to compare with. That is not to say that you don't need good sounding amps etc to get the venue rockin' and a satisfied audience that leaves saying that the sound system was the best they had ever heard...

Can you use different amps for hi/lo in a HiFi-system? Yes! But I recommend using similar amps. I used Nakamichi N620+N420+EC100 for many years and the sound was very balanced. Of course this configuration was intended by the manufacturer. My guess is that eg Linn LK140+LK85 would perform even better as they are also two versions of the same series of amps but with different power ratings.

If your speakers are simple 2-way with just a coil and a capacitor for filtering my recommendation is using two identical stereo-amps with one placed behind each speaker and low level passive x-overs that only employs 2 resistors and 2 capacitors for each channel. This is very simple, keeps the speaker cables short and leaves most of the PSU in the amps available for the woofers.

If the speakers have complex filters they usually not only divides the range and adjust levels but also includes phase correction components that may require some kind of delay line in the active x-over and you are in for a big challenge...

@danvignau I suggest using an EQ instead of touching the filter levels. Behringer have one that is digitally controlled 1/3 octave where you can save settings and recall them anytime you like and they are not very expensive. For normal use you will just of course leave it in "By-Pass" and if you want to keep it completely out of the signal chain simply connect it to the Tape Monitor Loop of the Pre-amp.

Good recordings does not in general need any altering but eg an old VHS- or cassette-tape might benefit a lot from some tweaking/restoration. You might also like to call it a REMASTERING and there is NOTHING WRONG with trying to get the most out of a crappy recording using whatever apparatus you like! Including EQ, Noise Reduction, Expanders or Sonic Enhancers etc... It is not "puristic" but it might sound a h_ll of a lot better and if that is the only recording you have there is NOTHING WRONG with trying to restore it "to its former glory" using what ever means you have available!

BUT: Don't touch the filters! They are part of the Amp-Speaker combination and should NEVER be changed once they are properly aligned! Of course that is just my humble opinion and you are of course free to turn any knob you want... :-)

@midareff1 I agree 100%! Two identical stereo-amps with one for each channel is DEFINITELY the best way to go when Bi-Amping...

BTW: I've gone back to passive x-overs but not with the original components in the filters but instead 14AWG Jantzen coils and their Superior Red Z-Caps.

Does this sound better or worse than my active Nakamichi arrangement?
Hard to tell since what is best since the amps and cables have also been altered.
At lower levels YES! But if I try to "wake up my neighbors": NO!

I ran the system in passive configuration with a Linn Majik-I and THAT sounded a h_ll of a lot better than the Naka combination but that little VERY NICE amplifier just did not have the oumff since it only produced 2x33W at 8ohms and that is not enough to drive my speakers to more than approximately 85dB.

So what is best? Active or passive x-overs?
There is simply no correct answer to this question!
They both have their uses and issues....

For high power systems: Go active!
For low level systems: Leave the speaker design to the manufacturer...

Of course it is a free world and anyone is free to do anything they want but the original question in this thread was about using different amps in Bi-Amp configuration and my answer is: YES, you can do that!

BUT: YOU will become a SPEAKER DESIGNER if you try!

Nothing wrong with that! There are thousand of them out there and you might be just as good as they are but believe me when I say that it is NOT an easy thing to design a good amp/speaker system.

It all boils down to what you want to do! Cracking the skulls of 75 000 people at an arena or sit at home listen to a singer-songwriter at "bedtime" levels?

If what you want is the first alternative: Go active!
If it is the second and you want to keep it simple: Don't bother!

If you are anywhere in between it is all up to you! :-)