Yamaha EMX640 mixer amp

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As far as I can tell this is the basic form to the power amp - what class is
it? and in general terms the operational bounds of the biasing, a lot of
diodes? seem to be involved.
Equi-spaced font needed for this ASCII, maybe properties/mesage details or
copied into text handler with "Terminal ","Fixedsys" font or similar
(only 2 emitter resistors, on two central Tr and chokes in the other emitter
commoned connections, all left out in the below )

 ----------------------  + rail
      |        |
    |/          \|
   -|            |-
    |>          <|
      |        |
      |--------|           all 2SD2560
           |
            \|
             |-
            <|
           |
           |---------- O/P
           |
            >|
             |-
            /|
           |
        |--|----|          all 2SA1647
        |       |
      |<         >|
     -|           |-
      |\         /|
        |       |
   --------------------- - rail






Re: Yamaha EMX640 mixer amp


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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.


Re: Yamaha EMX640 mixer amp


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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?



Re: Yamaha EMX640 mixer amp


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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.


Re: Yamaha EMX640 mixer amp



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,
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



Re: Yamaha EMX640 mixer amp


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.



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