Can you bridge any 2 channel amp?

B_limo, Only single ended amplifier can be bridged. Single ended means that one of terminals is inactive (ground). Some amplifiers have differential outputs and cannot be bridged (being already bridged). Bridging them will work but won't change output voltage - therefore won't change output power. In order to bridge amplifier phase of one channel has to be inverted. Bridging doubles output voltage and therefore quadruples output power but has some disadvantages:
- might not be able to drive some speakers since it requires double current hence it is the same as loading it with half of impedance. My amplifier, for instance, wouldn't be able to drive half of my speaker 3.8ohm min. impedance since it is specified at 3ohm minimum.
- second problem is that each amp would have to deliver twice power being not designed for that (power supply, heatsinks) and will likely overheat.
- third problem is amplifier's output impedance that will double and your speaker electrical damping will be twice worse.
- It might damage amplifier and will most likely void the warranty.

Even if you limit loudness to use only nominal power of each amp (double vs. quadruple) it is not worth it IMHO since it will only make it 22% louder. Amplifier's that are designed for bridging have most likely phase inverting switch plus oversized power supplies and heatsinks.

Csontos,

As Al stated dual mono might be "better able to tolerate increased current" but impedance issues are still there. One Audiogoner drives, with great results, 1 ohm planar speakers (Apogee Acoustics Scintilla) with 2ohm minimum rated class D amp (H2O M250SE) but it is an exception. These speakers are only 76dB efficient and require a lot of power but amp somehow can manage that. He worked on this project with designer of the amp.