Ring modulators / some comments

Rene Schmitz uzs159 at uni-bonn.de
Tue Nov 16 19:25:59 CET 1999

At 10:37 16.11.99 +0100, Martin Czech wrote:
>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.

Or two. Like the circuit from synthfool.

>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.

In the two transformer configuration you have one AC and one DC coupled
input, like seen on many other ringmodulators. So you have one dedicated
audio and one DC input.

>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 one uses transformers with two secondary windings, one can add a 
small trimmer to adjust the mismatch of the two windings. 

>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

Or the (Ge) AA112 which was used a lot in AM-tuners. 
Just a weird idea: What about using vacuum tube diodes. i.e. use two dual
triodes and tie the grid to the anode. They've got very soft knee.


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