[sdiy] real ring modulator schematics

[mbartkow at et.put.poznan.pl]

Glue Sniff <gluesniffinghunchback at yahoo.com> wrote:
 
>  When I said I was looking for "real ring modulator
> schematics",I meant one that accepts two inputs and
> then outputs the sum and difference of the two inputs.
> from what I understand balanced modulators only accept
> one input and they use an internal frequency as the
> second sound source and then output sum and
> difference. I have read that the sound is essentialy
> the same. but I wouldnt think this to be true if the
> two input instruments were different instruments or
> sounds. having the sum and difference of two inputs is
> what I am looking for if there is a bananced modulator
> out there than can do this then thats what I am
> looking for.

Hi there. I'm sure some will point you to RM designs
better than I would do. I am just going to clear the
terrible misunderstanding of the operation of RM.

To get a sum or difference of two signals you simply
need to mix them in phase (add) or with the phase of
one component inverted (subtract). Boring stuff.

Ring modulator is amultiplier, not an adder. It does
produce a product of two input signals or a product
of one input signal with some internally generated one.
It just happens that if both the signals are pure sine
waves the output is a sum of two other sine waves, whose
frequencies are the sum and the difference of the frequen-
cies of the input sines. NOT a sum and difference of the
input signals. This is a result of a smart mathematic
law that says sin(x)*sin(y)=0.5*cos(x-y)-0.5*cos(x+y).

In case of complex input signals (your instruments), the
output has a very complex spectrum which is a convolution
of the input spectra. BY NO MEANS IT IS A SUM AND DIFFERENCE.
Usually, this spectrum is so much complex that it is a
kind of almost unusable noise. Simpler spectra are obtained
by multipying one complex signal with a sine wave, which
is a reason to implement the RM with an internal oscilator.

regards,

MB