[sdiy] passive ring modulator transformers

[Richie Burnett]

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.)

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.

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

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.

-Richie, 

Sent from my Xperia SP on O2

---- Neil Johnson wrote ----

>Hi,
>
>Simon Brouwer wrote:
>> I imagine a big part of the sonic difference between the
>> transformer-and-diode-ring modulator and analog-multiplier circuits is the
>> nonlinear behaviour of the diode ring.
>
>A ring modulator is just a type of switching modulator - only the sign
>of the carrier is important, and the sharper the switching edges the
>cleaner the resulting output.
>
>Whereas the analogue-multiplier circuits are in the class called
>product modulators.
>
>There are many different ways of making switching modulators.  The
>original advantage of the diode ring and transformers was cost - in
>1934 "op-amps" didn't really exist, and diode choices were either
>thermionic or copper-oxide.
>You can kind-of emulate a switching modulator with a product modulator
>by driving the carrier input with a square wave.
>
>> If the transformers do not contribute a lot of distortion (assuming that in
>> this application they are not driven to saturation), they might be replaced
>> by opamp circuits without losing much of the characteristic sound.
>
>You can make a switching modulator with a single op-amp and a transistor.
>
>Cheers,
>Neil
>--
>http://www.njohnson.co.uk
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