ARP 2600 Ring Modulator #4014

[Don Tillman]

   From: WeAreAs1 at aol.com
   Date: Sun, 7 Mar 1999 17:12:13 EST

   I am currently trying to reverse-engineer the Ring Modulator
   submodule in an ARP 2600 (module #4014 revA).  I have removed the
   module from the synth and am now tracing out the circuit.
   Fortunately, this module does not have an epoxy casing around it,
   so all of the circuitry is visible.

Hi.

Consider yourself very lucky!  When I got my ARP2600, the Ring
Modulator was dead, so I went about fixing it, and sure enough, the
inside of the module was filled with white silicone material.  Yick.
Getting through to the circuit was hell.  A handful of parts gave up
their lives for the cause.

(It was an easy fix once I got it apart and figured out the circuit --
one of the opamps was dead.)

I transcribed a schematic of the circuit; and I'll be happy to post it
if anyone's interested.  It's a very weird circuit; I can't imagine it
has any advantages over a 1496.

   I am hoping that someone on the list knows the part number of these
   mystery transistors, and will share that information with me.  

6 of them are NPNs, 6 of them are PNPs.

I don't know the part numbers, but any quality audio transistors (low
noise, high beta) should do the trick.  The classic 2N5087/2N5210
should work very well.

  -- Don