Ring modulators / some comments

Martin Czech martin.czech at intermetall.de
Tue Nov 16 10:37:03 CET 1999


btw.

the audio transformers for a real ring mod are not quite cheap.
Farnel carries some, about 10 EURO each.
The basic passive circuit needs tree.

I think it is a good idea to combine the windings such that you get a
1:10 ratio or so. This way you can tune down the amplitude
in the diode ring without resistive divider (avoiding noise).
On the other end you can transform up again.
The amplitude at the diode ring must be very small, otherwise
severe speak through/distortion.

I noticed that the transformers can not cope with frequencys below -say-
40Hz (as predicted by theory), because in this case the trafos represent
a short to the driver.

So a real ring mod can not sweep into sub audio, not even near to this.
OTOH, it has a sound that differs from a pure electronic
active multiplier (intermodulation).

I've seen a proposal to replace the trafos by op-amps,
one inverting and one non inverting give a balanced signal,
and one can adjust the dc bias, thus feedthrough.

If this works at all, it will work for dc also.
Of course, noise get's an issue then.

One balanced driver for the carrier, one for the program input,
both with series resistance ~1k.

One balanced to unbalanced converter (difference amp).

A lot of trimming possibilities.

I saw this in an old Funkschau correlation meter proposal.

It makes a difference to use other band gap materials as well, ie.
Si or Ge (OA something) diodes (the later are seldom now), or even shottky
(BAT42).

In the past there were selected Ge diode quads, but I couldn't find
them anymore.

Anyway, it is worth the pain.
Diode ring mods have a more agressive sound, wheras a good linearized
active electronic multiplier can sound very soft.
If the carrier tracks the modulator in frequency, the effect are
not typical at all.



One main application is of course the processing of life/taped
sound, the ring mod is one of the modules that is really made for this
(along with vocoder and frequency shifter).


I used this a lot on my CD #2, eg. muldiplying a signal with a delayed
copy of the same signal. Or multiplying broadband life signals
with narrow bandwidth toms, gongs etc.

In this case the rhytmical effects are dominating.


There is really no specific ring mod sound, it depends
on the creativity of the user. 


m.c.




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