Can you bridge any 2 channel amp?

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.

Thank you guys. My reason for asking is that I've just had 3 Acoustat TNT200 stereo amps rebuilt with mono capability via internal switch. The work was done by Roy Esposito who is one of the design engineers of the amp. He assures me they are still stable at 4ohms in mono. It's not that I don't trust Roy, but you can't have too much consensus.

For the most part any transistor amplifier can be bridged, you need to run the output of one channel to the negative side of the input differential pair. Just follow the feedback of the amplifier to the diff pair, you will have to reduce the voltage from the output of the leading channel you will have to play around a bit to match the gain. Start with a 15K ohm 1/2 watt resistor and measure the amplitude of each channel, adjust the resistor until you have equal gain. Be aware the amplifier should be stable enough to drive a 2 to 4 ohm load in stereo if you intend to drive a 8 or 4 ohm load. The input will be the leading channel the one you are driving the back side of the diff pair with. The plus lead will be the leading channel and the other output will be the minus. This will now be a floating ground and can not be used with speakers like the polk SDA series that interact with between the umbilical cable, this will destroy the amplifier