How could one bridge a stereo power amp to mono? I have a stereo guitar power amplifier that I would like to bridge to mono externally to power speaker cabinents more effectively. Are there any pre-manufactured devices that do this? If not, how could I make one myself, and what should I watch out for?
No it´s not the speaker cabels you shall phase reverse, it is signal on inputs.
If your power amp have balansed inputs you can use a balansed Y-splitt cable and phase reverse one of the connectors.
It is very inportant that you feed the stereo power amp with one mono signal and that the input level controls on the amp are adjust to equal level.
Then you connect the speaker cable leads to the left and right positive terminals (negative terminals is not connected) and the negative speaker lead shall go to this amp half that you have don a phase reverse on.
As Jakob say, you must use the double speaker impedance compare what the lowest allowed speaker impadancse are on each amp half.
(if the amp lowest impedance are 4 ohms, you must use a 8 ohms speaker in bridge use)
If the inputs not are balanced you can use a 1:1+1 transformer. there the 1+1 windings feed each amp and one of the wndings are phase reversed . (or a 1:1 transformer phase reversed on one input)