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Is a stereo amp, when bridged to mono, by definition differential?

I've been reading about amps and the seemingly endless choices that designers make, and found myself wondering this, but haven't been able to find the answer. It would seem, if I'm correctly understanding the definition of differential, also called push-pull, that bridging the two sides of a stereo amplifier would, by necessity, be creating exactly this topology. Unless I'm missing something, of course, which may well be the case.

Thanks to those who understand such things much better than I for any clarification.

Also, those who'd rush to weigh in about the likely sonic benefits -- or detriments -- of such arrangements needn't bother, as that's not what I'm wondering about.

Thanks.

-- Howard

hodu
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cleeds
5,644 posts
 
Al's answer is a great answer to a tricky question. One clarification I would make to the OP is that differential amplifier and push-pull amplifier are not interchangeable terms. Push-pull amps can be balanced or unbalanced amplifiers.
hodu OP
312 posts
 
Thank you both for your responses -- they are much appreciated.

-- Howard

almarg's avatar
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almarg
9,670 posts
 
A further elaboration to the last paragraph of my previous post. When I said:
If the amp provides balanced inputs, and if in bridged mode one of the two signals in the balanced pair of input signals that is being used is routed to the circuitry for one channel, and the other of the two signals in the balanced pair of input signals that is being used is routed to the circuitry for the other channel, then yes, I would consider that to be equivalent to one form of a balanced amplifier.
The same conclusion would apply to an alternative approach in which the single pair of balanced input signals that is being used in bridged mode is simultaneously routed into two differential receiver stages, that are identical except that they would be wired so as to result in the outputs of the two stages having opposite polarities. With the output of one stage going into the rest of the circuitry for one channel, and the output of the other stage going into the rest of the circuitry for the other channel.

Best regards,
-- Al
 
atmasphere's avatar
atmasphere
11,575 posts
 
If the balanced input only operates when the amp is bridged, then it is considered balanced but not differential (even if the individual channels are differential). set up this way the Common Mode Rejection Ratio (CMRR) will likely not be very good. Some mbl amplifiers are set up this way.

If the balanced input works in both bridged and stereo mode, then its likely that it is a differential input and performance will be better.
lalitk's avatar
lalitk
5,055 posts
 
Howard, 

Incase you're shopping, ModWright KWA150SE amp should be on your top 5 list. The amp is transformer coupled at the balanced inputs then direct coupled throughout, fully dual mono, fully-differential and uses no global feedback. It is a powerhouse in bridge mode capable of whopping 450W in 8ohms. 


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