PA amp - stereo or bridge?

[NHM]

Hi BCers

I can't get my head around the 'stereo or bridge' switch on our PA amp.

We run a stereo PA amp into two speakers, left and right, fairly standard I guess. However, everything is mixed to mono at the desk. Is there any advantage in setting the PA amp to bridged mode?

[Dad3353]

In 'stereo' mode (or, in your case, two distinct mono channels...), if one amp fails, the other keeps going. In 'bridge' mode, if either amp fails, the whole PA fails. In reality there's little chance of that, so, just for simplicity's sake, I'd keep the 'stereo' mode, and be able to set the volume level separately at each side (useful in an asymmetric stage set-up, for instance...),which 'bridge' mode won't allow, either. Phonically, for the audience, there's no perceived difference.

'Bridge' mode would be useful if expanding the PA, doubling the speakers, for instance, and adding a second, equivalent, amp, as it permits getting the full power from the amp, to drive one side of the new PA rig.

Hope this helps; subject to completion, correction and/or contradiction from others.

Edited October 21, 2019 by Dad3353

[NHM]

That's really helpful, thanks.

Funnily enough we used the asymmetric approach last night (although we called it, 'turn just that side up'), handy for a weird shaped pub in a weird shaped world.

… which wouldn't have worked in Bridged mode...

[Dan Dare]

You need to watch the impedances in bridge mode. Normally, a power amp that will run into two 4 ohm speakers in stereo will need to see 8 ohms in bridge mode.