Doepfer

--- 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.?