PLAN B analog blog

On the Buchla to Euro conversion, I built one of these boxes for a guy
who bought a Source of Uncertainty from Roger Cordell when he was
dealing Buchla.   The guy wanted it for his Doepfer system.  We ended
up getting him a two module boat and a blank panel and I used that for
the banana converters, which also serves as level converters.  It was
cool because we located the outs at the proper positions so he could
use shorting blocks to get to all the SOU I/Os.

It' a snap.  I can't make it for you as it would take too long to get
the time to do it, but I can surely  assist in the schematic. 
Basically it requires a separate module powered at +/-15 which
amplifies for Buchla levels in one direction and cuts attenuates on
the other. 

Let's deal with the Doepfer to Buchla conversions first: 

The first conversion are the gates and triggers. If I remember
correctly, Buchla gates are 10 volts and triggers are 12 and higher? 
Probably the other way around, knowing my luck. In any event, a simple
voltage follower powered from 15 volts with the proper value zener
diode hung on the output does that job nicely.  If you're nervous
about loading the zener to much, put a series resistor form the OP Amp
outout before it hits the zener which is tied to ground.

For the CV amplification FROM Euro TO Buchla, two inverting op amps
back-to-back which amplify the Doepfer signal 30% - this will get you
in the proper ballpark.

On the FROM Buchla to Euro conversions...there are some Doepfer inputs
which will fry with CV's that are too hot, so it's best to use a
simple voltage divider/attenuator to cut those down.  Very easy.  Two
resistors, the signal going into one, the other tied to ground, then
you tie the other ends of those two resistors together and take the
output from that point.  The values of the two resistors determine the
attenuation level.  If you don't want to deal with formulas, the use a
pot first (see below) and once you get the attenuation dialed in, take
an ohm meter and measure the resistance from both sides of the wiper
and replace those with fixed resistor values.  If you can't get exact
matches, either round down or multiply both values by a factor of X, X
being the amount which will get you closer to the ratio.  It's the
ratio you're after, not the values per say.  High resistor vlaues wil
create more current, but it's negligable.

Another way which is even easier is using a trim pot.  tie one end to
ground, the other end to the signal, take the output from the wiper. 
You'll have to dial in the scaling, but it's a set-and-forget thing. 
Every once in a while you'd have to calibrate them.  If you don't want
to deal with that, use the first method.

The only that that's a bit tricky is scaling for the Buchla keyboard
inputs, which are 1.3 volts/octave.  Wat you do is amplify the Doepfer
signal via the method listed above to a leel that's too hot for the
Buchal input, then put an attenuating trimmer on the output - just
like the one listed above, which you'll then use to scale the
amplified Doepfer output to the 1.3V/octave limit.


I believe Kevin Hayward (who was in your area) is still in Germany. 
If not, there's a local cat who could nail this for you in a flash.
Also Scott Evans.  Remember Scott Evens, General Manager?  He's stil
around and he could bag this easily.  Contaqct me off line for email
addys for both guys if you don't have them.

Hope this helps.


- P





--- In PLAN_B_analog_blog@yahoogroups.com, Chris Muir <cbm@...> wrote:
>
> 
> [Sorry if you see this message twice. My mail program burped]
> 
> At 6:32 PM +0000 5/26/07, (i think you can figure that out) wrote:
> >There are two Linear CV Inputs on the Model 15 - it's the two with
the bipolar attenuators,
> >both labeled FREQ VC
> 
> So, I'm still a little confused. Reading a little further down this
thread, I see that RSA says that the FM Jack is linear FM (which I
would hope and expect). And I assume that the two CV inputs are really
exponential. If so, this is good.
> 
> 
> >Good to see you posting here, Chris!
> 
> Thanks Peter, it's good to be here (I've been lurking for a while.)
> 
> As you may have surmised, I'm considering what to get for a
suitcase-sized Eurorack system to compliment my Buchla. The Plan B
family of modules seems to be shaping up quite nicely. It's really
close to being a complete system, I would only have to get a couple of
modules from other designers.
> 
> I still haven't figured out what to do about voltage & trigger
conversion to allow the Buchla to integrate with the Eurorack system.
> 
> -C
> 
> -- 
> Chris Muir           | "There are many futures and only one status quo.
> cbm@...         |  This is why conservatives mostly agree,
> http://www.xfade.com |  and radicals always argue." - Brian Eno
>