Can you bridge any 2 channel amp?


In the risk of sounding dumb, can you bridge any 2 channel amp? Can you not just twist the pair of negative outputs together and then the positive outputs together and then plug them into your speaker? I'm pretty sure you can't but I thought I'd ask the experts!
128x128b_limo
It's pretty rare that you CAN bridge a 2 channel amp. Unless the amp has a mono/bridge switch or jumpers, you can't. Most do not.
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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.
What you describe is not bridging, it's paralleling. Aside from some MacIntosh models and a Bryston factory option, most SS manufacturers don't advise this.
Kijanki, does this line of reasoning hold true for a dual-mono design with separate power supplies, transformers and heat sinks? Would impedance issues still be a factor?