--- In Doepfer_a100@yahoogroups.com , "Tim Stinchcombe" <timothy@...>
wrote:

>
> Hi Peter,
>
> I've just had a quick play around with this idea, and thought I'd
> offer up a few comments.
>
> The transistors in the MC1496 chip used for the Y input are kept
> biased at around 6V by the coupling cap, C2: thus if C2 is shorted,
> then a 6V input on the Y input gives zero gain, and dropping the
> input below 6V gives increasing *negative* gain, hence
> the 'inversion' effect. If you now supply a bipolar signal to the Y
> input, when it goes negative, you are getting much more gain than the
> design was intended to, and so the transistors in the chip begin
> to 'hard switch', i.e. you get distortion, and (for a sinewave input
> on X) the output will be much squarer than it would otherwise. This
> is most likely the 'timbral differences' you can hear, i.e. you also
> have odd multiples of the frequency of the X input signal.
>
> On the other hand, the transistors used for the X input are biased
> around ground anyway, therefore shorting out the other coupling cap,
> C10, instead, means you don't get these drawbacks, and quick
> experimentation showed that normal amplitude modulation was easily
> achievable this way.
>
> I'll see if I can easily convert my scope traces to a gif file, and I
> could then post it to the files section, if anyone is interested!
>
> Tim
>
> --- In Doepfer_a100@yahoogroups.com , "(i think you can figure that
> out)" <peter@b...> wrote:
> >
> > This may be the only mod which will take you less time to do
> > than it will to read this letter. I could have *sworn* i had
> already
> > posted this...i actually remember typing it, but possibly old age
> > has effected my memory along with my sexual stamina.
> >
> > Anyway, if i have posted this and for osme reason I just can't find
> > it, please forgive the aged of the list.
> >
> > You can convert one (or both if you care to) of the A-114 Ring
> > Modulators to DC coupling with a single solder bridge. Takes
> > about a second. It will give you DC coupling capability - in
> short,
> > the Y input wil now accept DC voltages, making your A-114 a
> > VCA (footnote required - see below). At very least it does also
> > give timbral differences from the AC coupled half (you get both
> > the X and Y sum frequencies I believe with DC coupled
> > multipliers). Totally worth the one minute it'll take to do it.
> >
> > Here's how!
> >
> > 1) Take your unit out. No, not THAT unit...the A-114.
> >
> > 2) You'll notice two capacitors on the board in which the long
> > dimension of their case is parallel to the faceplate. One is for
> > the top half, one is for the bottom. All you have to do is bridge
> the
> > two contacts of that cap and you're done. You don't even have to
> > remove the component. It doesn't get any easier than that, babe.
> > You can do this with just a solder bridge or by running a
> > component lead across the two contacts and soldering that in
> > place. I happen to be rich in cut component leads around here,
> > so i opted to do it that way. One less to sweep up at the end of
> > the day.
> >
> > The differences between the AC and DC rings are significant. I
> > keep one as is and mod'd the other. There's room on the
> > faceplate to add a switch so that it could be selectable between
> > the two states, but with two rings in one module it doesn't seem
> > practical to do that.
> >
> > (footnote: The DC response of the DC coupled Y input is
> > inverted (180 degrees out of phase with the input) In short, if
> you
> > were using this as a VCA, the greater the voltage put into the Y
> > input, the more attenuation at the output (output gets softer).
> > Usually it's the other way around. No big deal, the sonic
> > characteristic of the DC Ring is still worth it. If you wanted to
> get
> > fancy, you *could* add an inverting op amp or discrete transister
> > inverter bwteen the Y input and the cap to put the control
> > response back into phase - that's up to you.)
> >
> > Try this one - you'll like it. And again if for some reason I have
> > already posted this and just kind find it....be kind to the ancient
> > (and stupid) among us, namely me.
> >
> > - P
> >
>

What would happen if you shorted both c1 amd c2 on the same unit.