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
>