[sdiy] Yamaha CS80

[WeAreAs1 at aol.com]

In a message dated 3/19/02 1:17:08 PM, Linc at christeld.freeserve.co.uk writes:

<< I've been given a CS80 for a short while with no footpedals or 
instructions.
On the front someone has put a label: 'Important, connect footpedals before
switching on'. As a bodge can I put a tip-ring shorted quarter inch jack in
the footpedal (expression) socket or is there something special about the
proper pedal? Is it just a potential divider and where can I get one? I know
a volume pedal could be rewired but would this give an adequate range from
nothing to full level?

I'm assuming no sound will come out without the pedal and that no harm would
actually occur if it were switched on.
 >>

The CS-80 (and almost all of Yamaha's pre-1987 instruments) used an optical 
footpedal.  It contained a photoresistor and a smal incandescent light bulb.  
The pedal moved a little "curtain" between the light bulb and the 
photoresistor.  I think that one of the three terminals was DC voltage for 
the bulb, the other two were ground and the "wiper" of the photoresistor.  
The early DX7 volume pedals worked pretty much the same way.  Unfortunately, 
I don't have access to the schematics right now, so I can't give any more 
detailed help.  For safety's sake, you probably shouldn't directly short any 
of those wires to ground (without some sort of current-limiting resistor in 
series with the short, at least 1K).  Maybe someone who has the schematics 
will chime in here...

Mike B.