Gareth Magennis wrote in message
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"N_Cook" wrote in message
...
N_Cook wrote in message
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repair m on e-S and there is an inverter stuck in before the R ch o/p,
not
for the L





Is it just for evening up the ps?. If a momentary high draw from one PA
on
+/ve rail dropping reservoir by 1V then also a matching 1V drop on
the -ve
rail from the other ch, wheras usually that would be a 2V drop on + rail
only






Yes there is a specific reason/technique involved in running the outputs
"out of phase" and inverting the signal to one channel.
Yamaha also do this with the Stagepas range, Lab Gruppen do this with
their
far more pro series of amps. There are others. You can get more out of
the power supply by doing this.


I personally consider the technique fundamentally extremely dodgy, since
the
"ground" connection on one of the amplifiers is actually live, which is
not
at all obvious to anyone not in the know. In the case of the Stagepas,
you
have 2 speaker jack outputs next to each other. Plug in 2 metal jack
plugs
to your speakers and you have the almost unimaginable situation of 2 jack
plug bodies a few mm apart, with a power amplifiers output between them.
If you use right angled metal jack plugs, a dead short and a blown amp is
pretty much a certainty at some point, as is accidentally touching
anything
grounded against the one live speaker output jack plug body "ground"



Gareth.





Not rectified mains , EMI filtered mains. If I see this amp again I will try
running reduced via variac to see if there is some imbalnce reflected in L
and R channel throughput or metering. Reported as loss in volume , rather
than clipping, for a while and then drop out of L ch , and reflected in
meter reading. Owner thought a problem at speakon connectors as waggling
there affected the signal. No problems on that board but a cable tie
mechanically connected the board to those downstream mains delivery wires
going to the problem spades.