VCDO / RC4151

[WeAreAs1 at aol.com]

As Terry Michaels pointed out, the RC4151 is second-sourced by Exar, as the 
XR4151.  You can pick up a pdf datasheet at:   
http://www.exar.com/products/xr4151.html

It's an 8-pin IC, and described as a voltage-to-frequency or 
frequency-to-voltage converter.

I found it today in a fairly recent Jameco catalog as Jameco part #29372.  
The price is $1.19 each.

It should be noted, however, that the Rhodes Chroma didn't use the 4151 as 
its actual oscillator.  It used it to perform the reset function on a more 
traditional temperature-compensated, expo-driven, opamp-based sawtooth 
integrator (the service manual refers to it as the "retrace" function - is 
this the same thing as reset?).  The purpose for the 4151 was to ensure that 
the sawtooth would reset with the sharpest possible edge, and have no 
high-frequency pitch droop.  This is what makes me think that it might work 
well as a wide-range voltage controlled high-frequency clock (with the 
addition of a proper saw-to-square comparator, of course)

I'll try to draw up a schematic of this VCO later tonight, and mail it to 
those who would like to see it - or post it to the list, if it's sufficiently 
small.

Michael Bacich