I recently bought a Marantz 4400. This is one of the models of Quad receivers that Marantz made that the amps could be bridged for higher output in stereo mode. It is rated at 125w x 2 and 50w x 4. How can the stereo output be more than the sum of the output of two of the quad amps?

When bridged, the output voltage is doubled over that of a single channel. For a given impedance, ohm's law demands that the current must double as well. In that case, bridged power would quadruple over a single channel assuming the amp can provide the required amount of current. In practice, the current demands are usually a bit too much for that, and the power increase is lower than theoretical, but still more than doubled.

To use math, if we use (P=V²/R) to represent the power from a single channel...
when 2 channels are bridged into one, V becomes 2V and the power will be [P'= (2V)²/R] which is (4V²/R), or 4 times the original power.


-Tim

Thanks for the lesson.

Mike