Yamaha EMX5016 mixer amp from 2006

When I reassemble it I'll double scope the outputs, but anyone know if one amp output , to the output board that is, is inverted relative to the other somewhere.? For the 1/4 inch outputs , violet,A, L ch is normal sleeve ground but yellow ch is tip ground. Likewise the paralleled speakon outputs , inner and outer contacts are swapped between channels. BTW to work on this amp in 2 halves , you need to fudge a chassis ground interconnect

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.

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First looking at output board, knowing L ch was flakey, saw that there was no continuity to R ground of a 1/4 jack plugged in, eventually deducing that continuity was to the tip.

Anyway all PbF "usual suspects" dealt with on output board,ps and relevant shannels of mixer panel. PA section not touched, inputs swapped to isolate if the problem emerged (owner having to swap L and R speaker leads), would isolate to mixer or PAs problem. Unlikely pa problem as L ch of meter dropped , nothing on schema indicating meter feed from PAs . I was just wondering, as the feed for the ps is unipolar rectified mains and there was an obvious PbF failing on that. Especially as problem noticed at switch on, no great load, whether the raw DC feed reducing due to intermittant crimp contact could have led to a mior supply dropping and thence registering as 1 ch problem on the bargraph meter.

Run for 6 hours since, by owner, with problem not emerging.

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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.