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Dave Platt Dave Platt is offline
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Default Thoughts on this little oddity, anyone ...?

In article , Baron wrote:

What am I missing here ? Not of any real consequence, as the unit is
mended and back in its original condition, but for academic interest,
it would be good to understand the designer's thinking.

Arfa


I'll bet that your first suspicion is right and the amps have or are
being used in bridge configuration in some other gear.


There's another possibility, which I saw mentioned a few years ago.

By configuring the amp so that the two channels are operating in
opposition to one another, you may increase the amp's ability to
handle short periods of very high output (brief peaks) slightly.

The reasoning is this: most of the time, high-amplitude signals are
going to be in phase between the two channels. If the two channels
are operating with the same polarity, they're both going to be drawing
on the same power-supply rail during these peaks (i.e. both will be +
or both will - at any given moment). This sudden load will tend to
draw down the power-supply bypass cap for that rail, and/or will
result in a large amount of current flowing through one side of the
power supply rectifier chain. The other rail's supply capacitor won't
have any load on it at that moment, and its rectifier won't be
carrying much if any current.

On the other hand, if you invert the audio signal coming into one
channel, and then wire up the output of that channel to the speakers
"backwards", you end up with a situation in which the two channels are
usually drawing power from _opposite_ power-supply rails. This will
decrease the worst-case sag in the rail voltages, and also tend to
reduce and even out the current flow in the rectifiers (and reduce
voltage drop and heating slightly).

As a result, an amp which was designed with a "not-so-stiff" power
supply system, may be able to deliver a slightly higher amount of peak
power before it begins to clip and distort.

--
Dave Platt AE6EO
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