Doepfer

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

> 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. 

The A136 works fine as a voltage inverter. The A116 might possibly 
as well. My A119 doesn't have any voltage inversion capabilities.

> Since I don't have any space left in my rack, is there an easy way 
> to construct a little outboard CV inverter? 

Mount an A175 in a little box with a wall wart, or the Doepfer 
mini-bus board/power supply.

Joe

--- In Doepfer_a100@y..., "buechlerjoe" <buechlerjoe@t...> 
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. 
> 
> The A136 works fine as a voltage inverter. The A116 might 
possibly 
> as well. My A119 doesn't have any voltage inversion 
capabilities.

Actually, when I send a sawtooth signal to my software 
oscilloscope, it shows up mirrored on the screen. When I patch 
the signal through the A-119 (Asym. In) before sending it to the 
computer, the waveform looks the way it does on the front of the 
module. So it seems that the A-119 inverts audio signals. 

I believe the electronics involved in inverting a signal are 
extremely simple (although I don't know what they are) which 
makes me think it might be possible to fit the components into a 
connector or something to be placed in between two patch 
cables.

> 
> > Since I don't have any space left in my rack, is there an easy 
way 

> > to construct a little outboard CV inverter? 
> 
> Mount an A175 in a little box with a wall wart, or the Doepfer 
> mini-bus board/power supply.
> 
> Joe

Okay, a triangle wave from an LFO thru the A119 does indeed get 
inverted, but with a definite time lag. Suspecting a cap, I tried 
patching in the CV source instead. The DC was indeed blocked by the 
A119.

Although the A136 will indeed work as a voltage inverter, I forget to 
mention the hard clipping issue, which would affect LFO signals and 
Pitch CV among others (see my earlier posts on the subject). These 
would require an attenuator on the front end, compensated for by 
applying some gain to the output. The setup would require calibration 
if you needed exact -1 gain, but that wouldn't be important for most 
applications.

Joe

 --- In Doepfer_a100@y..., "mdimmm" <mdimmm@y...> wrote:

> --- In Doepfer_a100@y..., "buechlerjoe" <buechlerjoe@t...> 
> 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. 
> > 
> > The A136 works fine as a voltage inverter. The A116 might 
> possibly 
> > as well. My A119 doesn't have any voltage inversion 
> capabilities.
> 
> Actually, when I send a sawtooth signal to my software 
> oscilloscope, it shows up mirrored on the screen. When I patch 
> the signal through the A-119 (Asym. In) before sending it to the 
> computer, the waveform looks the way it does on the front of the 
> module. So it seems that the A-119 inverts audio signals. 
> 
> I believe the electronics involved in inverting a signal are 
> extremely simple (although I don't know what they are) which 
> makes me think it might be possible to fit the components into a 
> connector or something to be placed in between two patch 
> cables.
> 
> > 
> > > Since I don't have any space left in my rack, is there an easy 
> way 
> > > to construct a little outboard CV inverter? 
> > 
> > Mount an A175 in a little box with a wall wart, or the Doepfer 
> > mini-bus board/power supply.
> > 
> > Joe

> Since I don't have any space left in my rack, is there an easy way 
> to construct a little outboard CV inverter? 

I remember having a similar dilemma last year after my frames were 
full, when I realized that I needed an A185 to buffer the pitch CV 
from my A155/156. After spending a day considering which module was 
getting voted off the island, I ended up downgrading an A111 to an 
A110 to make the 4U available.


You might also install an extra minijack in the little box, and patch 
it into the A176 and draw power from that.

Joe

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