Yamaha EMX640 mixer amp

Looks like a lot of amps I see these days. Don't know for sure the "class" but I suspect it's pretty conventional AB.

Those outputs are Darlington, by the way, so obviously there's an additional

1.2 volts to be accounted for in the biasing...

Mark Z.

class

or

additional

Assuming its rating at 200 watts into 4 Ohms is per (non stereo) channel , it does not seem right that all that current goes through 2 output TOP66 devices. I've not found any date so far, mixer section not looked at yet. Does roundel stamp on the [cb with Japanese script on top and bottom sections and 86 12 15 across the middle mean 1986?

The B1647 and C2560 are pretty high-rated devices. 200 into 4 ohms doesn't seem _too_ over rated to me.

I commonly see them in consumer audio in their higher end model surround receivers, that is the ones rated over the standard 100 per channel, more like 120 into 8 ohms. So as I say, 200 doesn't seem too far off, perhaps just a bit of a stretch.

Mark Z.

,

yet.

All power devices share the same h/s 6 of these per ch, bridge rect,

7815,7915 no special treatment for those final 2 per ch. No fan assist, large convection area out rear only. Get into the mixer later for 7 more problems in there, so probably will find a more reliable date

Datecodes on TTL likely 1997 , much more likely

86, 12, 17 on this inspection ink stamp roundel so 86 is not 1986. Amazing they could keep using on one ch as long as they did, only stopped when an intermittant squeel got too frequent. pcb crack half the height of the mixer board. Edge reinforced , other end drill hole crack limited now and major traces drilled/bridged with metal , so can safely handle to deal with all the other traces. I knew the amp had been dropped from the rear panel bent by the tr inertia. So stove in from the front as well.