[sdiy] passive ring modulator transformers

[Neil Johnson]

Hi Richie,

> Neil, in practice the diode ring modulator is somewhere in between the "product generator" and the "switching modulator" that you described. There is some proportional multiplication behaviour going on there because of the incremental resistance of the diodes. (They don't switch abruptly from fully blocking to fullt conducting.)

Any resistance in the diodes is an imperfection, which is balanced out
to reduce carrier bleed.  As long as both directions see the same
resistance then that should cancel out and no carrier seen in the
output.

> The diodes can be made to switch sharply by over driving one of the inputs, or using a square wave like you said, and this is often the case in RF mixing applications where you're just interested in a single IF frequency at the output, and filtering away all the other crap.

Here's a rather useful video showing a ring diode mixer in action on the bench:

https://www.youtube.com/watch?v=junuEwmQVQ8

The original application for the ring modulator was in telephone
circuits, where it was used for FDM'ing telephone channels together.
See the original Cowan patent for background.

> But it certainly doesn't have to be like that. It's not a strictly on/off modulator, it is *a bit* proportional too :-)

Yes, it's quite funny that the world of electronic music has taken the
ring modulator and kind of claimed it as its own - see the wikipedia
page on "Ring Modulation" for example: almost the entire content, and
list of references, are in the electronic music domain.

> Sure you could introduce non-linearities into a mathematically perfect double balanced modulator though to make it sound like a vintage diode ring modulator. Someone wrote a very good paper on a digital algorithm for modelling a diode ring modulator, but I seem to have the link saved.

Did you mean this one?  http://recherche.ircam.fr/pub/dafx11/Papers/66_e.pdf

Cheers,
Neil
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