The 2500 manual describes this as
" a balanced modulator, a VCA with certain associated circuitry"
It's very much like your standard ring modulator.
There the output consists of the Sum and Difference of the input frequencies
(but contains neither of the input frequencies).
The ARP 2600 used analog multipliers in contrast to the ring of diodes found in many RMs.
I wonder if the 2500 has a similar circuit.???
GuitarFool has the schematics here:
The schematics for the 4014 Balanced Modulator which I think is related to the 1005 modamp
have two 2-Quad Multipliers.
The submodule in the 2600's case was the ARP 4014.
The schematics from ARPtech are here
One of the nice things about the 2600 was its switch that allowed you to select between
AC-coupled and DC-coupled modes.
Anyway, the 2500 manual describes the 1005 module thus:
"The Balanced Modulator" can accept two input signals A & B in the frequency range DC to 20KHz
and will produce the output function (A x B/10)......If f1 & f2 are chosen properly, the output will be a complex wave with inharmonic overtones".
One of the really cool things about the 1005 ModAMP is that it produces two DC control voltages.
(CVA & CVB).
CVA & CVB - the 1005 outputs control voltages
In this video example (below) I'm using the CVs to modulate the VCOs.
You can download the audio files from the above video here:
Turning the ModAmp is easy with the illuminated on/off button.
This on/off switch can also be operated with a gate. (the input is marked "Mod Gate" on the bottom & top of the module).
The Mod Gate
At the top, there are an "unmod" & a "Mod" input.
Upper half of the 1005
The Manual states" a Pulse applied to to either input will switch the operating mode to either"unmod" or "Mod".
The mode will remain as set until a pulse is applied to switch to the other mode,
or until the mode is changed by the button.
Finally, the 1005 has a VCA.
We have a switch to choose between linear & exponential control.
And there are lots on CV inputs from both the upper & lower matrix sections.
Heaps to play with.