[sdiy] On the topic of ring modulation (Using FETs instead of diodes?)

[Richie Burnett]

The original diode ring modulator works on the incremental resistance of the diodes changing when the forward current varies. So you are using the non linear I/V characteristic of a real diode to approximate a multiplier in the same way as the moog ladder filter relies on the incremental resistance of the base Emitter junction of transistors to make a variable resistance in a filter circuit. 

So it wouldnt work with ideal does because they don't have modulation of their incremental resistance with forward current. 

-Richie,

Sent from my Xperia SP on O2

---- Tom Wiltshire wrote ----

>
>On 14 Aug 2014, at 19:43, Donald Tillman <don at till.com> wrote:
>
>> 
>> On Aug 14, 2014, at 6:03 AM, Tom Wiltshire <tom at electricdruid.net> wrote:
>> 
>>> Perhaps you could try using four precision rectifier circuits in the ring configuration to overcome the diode turn-on threshold. Diode ring modulators usually use germanium diodes for the lower threshold voltage, but with the precision rectifier circuit, you could probably use cheap silicon diodes - 1N4148s or whatever.
>> 
>> It wouldn't be a ring modulator. 
>> 
>> The diode ring modulator depends on the diode nonlinearity, which the precision rectifier circuit doesn't have.
>
>I realise that the non-linearity of the diodes adds distortion to the traditional diode ring mod, but I thought that the distortion was an unavoidable side-effect, not the whole deal. It'd still be a ring modulator even with ideal diodes, wouldn't it? (zero threshold voltage, no nonlinearity at signal levels)
>
>If it would, then a precision rectifier might get you closer to ideal. Ok, it won't sound like a diode ring mod any more, since it won't have the heavy distortion, but it might be a simple/cheap way to get a cleaner ring mod sound like you'd get from a analog multiplier like AD633.
>
>Does anyone else have an opinion on whether this is a workable idea? I can't go and try it right now...
>
>Tom
>
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