Doepfer

I have not read all of the replies to this, but I do have two solid 
answers on circuits you can make quite easily yourself whiuch 
will do what you need.

There is a CV scaler circuit on Chris McDonald's DIY page that 
will do invertions.  i have built a few of these, they work like a 
charm.

Go here:

http://www.evenfall.com/diy/cvscaler.html

There is an even simpler method, which I will try my best to 
describe here in text:

Get an op amp. Connect the power (both - and + - do not us a 
single supply comparator).  Make an input t (in which you would 
connect your CV) and run it through a 10K 1% resistor.  Take the 
output of that resistor and route it  to the  '  -  '  (inverting) input of 
the op amp.

Now, run a standard feedbackloop  from the output of the op 
amp also to the - input of the op amp through a resistor.  this 
feedback should be another 10K 1% resistor as well.

Run another wire directly off the input and connect it to one side 
of a 10K pot

Connect the other side of the pot to ground.

Connect the wiper of the pot into the + (non-inverting) input of the 
op amp.

To match the Doepfer impedance, you should run the output of 
the op amp also through a 1k resistor.

The output side of that 1K will give you a voltage which can be 
scaled either negatively or positively depending on the setting of 
the pot.

This will allow you to process an input as Buchla did it - you can 
adjust the level (amplitude) of an incoming CV either  
non-inverted ot inverted, with the ecenter point of the pot being 
null (fully attenuated).

I have another circuit which will yield a positively biased 
inversion, but I don't think this is what you are asking for.  In this 
instance,  +5 would become ground and ground would become 
+5.

So there you go,

Peter Grenader






--- In Doepfer_a100@y..., "mdimmm" <mdimmm@y...> wrote:
> 
> Are there any other modules besides the A-175 that do voltage 
> inversion of CV? (A-119, A-116, A-136?). The A-119 doesn't 
> seem to handle CV signals very well, seems more suitable for 
> inverting audio signals. 
> Since I don't have any space left in my rack, is there an easy 
way 
> to construct a little outboard CV inverter? 
> Would the polarity switchers cable manufacturers sell work?
> 
> Thanks a ton.
> 
> M. Dimm