MOTM

In a message dated 2/7/02 9:49:12 PM, motm@yahoogroups.com writes:

<<  "corelli44" <john@...> wrote:


Hello List,


I have an old Volume/Modulation pedal that I got with my original DX7 

back in 1985. I'm trying to measure the resistance to see how to use 

it with the pedal interface but I'm not getting very clear numbers.


I get readings between 25 and 40 most of the time with the pedal up 

or down. It does go up to as high as 150 sometimes but very briefly 

(could this be my DVM? It's quite cheap). 


Also, I only get readings with leads on the very tip and behind the 

first ring on the plug. I get nothing with one of the leads between 

the two rings (and the other on either side of either ring). Is this 

the way the newer Yamaha pedals are wired?


I'm just wondering if older pedals might have been made a bit 

differently than the newer Yamaha pedals or if they should be 

somewhat similar (if anyone has any experience with older pedals). 

 >>

The foot pedal you have is a model FC4.  The pedal they are currently making 
is the FC-7.  The old FC-4 is an opto-electric pedal.  It contains a small 
incandescent light bulb and a photoresistor.  Two of the TRS plug conductors 
are connected to the photoresistor; the other conductor supplies DC voltage 
to the light bulb.  Movement of the pedal opens and closes a small shutter 
between the bulb and the sensor, allowing in or shutting out the light from 
the bulb.  With no power applied to the lightbulb, moving the pedal (opening 
and closing the window) won't really change the measured value of the 
photoresistor (it's dark in there!).  This is in contrast with the newer 
"passive" FC-7 pedals, which are potentiometer-based, so their resistance can 
be varied with no power connected.

For more reasons than one, it's probably a better idea for you to try to 
obtain one of the newer pedals for use with your analog equipment.

Michael Bacich