Inverting attenuators

[Coriolis]

I see that Serge-fans rave about having attenuators with inverting capabilities on cv-inputs. Makes sense I guess, giving more functionality using less space.

So where would you put them, if you were building a synth? Do they make more sense on some modules than others?
I'm thinking about going that route on my modular, which I'm designing at the moment, but I'm thinking the decreased adjustability (cutting the pot sweep in half) wouldn't be worth it on all modules?

Any input on this?

C

[blue hell]

Clavia used inverting inputs for their "voltage" controlled envelope modules on the NM Classic, this sort of makes sense as usually higher notes should be shorter than lower ones and the pitch control voltage can directly be used then to control the envolope attack, decay and hold times.

[Coriolis]

Hmm...I'm not quite sure I understand what exactly inverters would do in that application. I thought ADSR's were used with positive going voltages only? Maybe I'm thinking of gate signals?

I do understand how inverting the output of an ADSR could be useful though...

C

[blue hell]

I was refering to voltage controlling the ADSR times.

[Coriolis]

So: having an inv att on the cv input of, say, attack time, Instead of having the range of the adsr going from 0v to +5V on a regular pot, it would go from -5v to +5v on an inverting attenuator, or what? And what would the negative portion of that do? Nothing? Negative attack time?



C

[Scott Stites]

As you mentioned, you wouldn't want them in places where you want that fine range of control - full sweep of the pot certainly helps there. This would include modulation inputs for VCOs, for example. A little voltage goes a long way when setting up a vibrato, chiff or trill.

Sometimes, I'll put both an attenuverting input and a non-attenuverting input to a device in those cases. Better yet, if you have some spare space on any module, plant an attenuverter there - an input, an output and a pot. With this you can patch the output to any input that doesn't have an attenuverting CV input. If you use 1/4" or 1/8" connectors, the added bonus is that this circuit can double as a bias source. If you normal the input connector to, say, +5V, you can get a variable +/-5V bias voltage from the output if nothing is plugged into the input. Bias voltages are very useful to have around.....

Cheers,
Scott

[blue hell]

[Coriolis]

Using banana-jacks here, so no bias for me, but attenuverters as a sort of utility-space-filling element makes sense, except it means using more panel space instead of less, I think. But perhaps having attenuverters dispersed on various modules might make up for that.

I guess I need to get some experience using inverters...

C

[fonik]

i found the buchlatype processing very helpful. the incoming cv processed by a +/- attenuation pot, an offset pot and a lag pot (optional). it's worth a module on it's own, i think. you may take a look at this:

---

dvp.gif
Description:	Dual Voltage Processor (Peter Grenader, personal use only)
Filesize:	56.68 KB
Viewed:	331 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

[Coriolis]

Very nice! Offset could be useful...
But where would I put the optional lag pot you talk about?
And what does it do?
Sorry for being a bit of a pain...

C

[jksuperstar]

Sounds like a good use for those old fashion dual-pots (a small one mounted ontop/within a larger knob), or one of those push=1thing/pull=another like they use on some car radios (volume/bass, etc).

[fonik]

[fonik]

concerning the voltage processor i'd recommended to replace the 10k resistor at the negative input of the first opa by a 2k 10T trimmer (used as variable resistor) and a 9k1 resistor in series. this way you can use a center taped pot and calibrate the circuit.

[Coriolis]

Thanks fonik, those look nice and easy to try, and probably deserve a module of their own as you say.

So, if I understand correctly, the lag circuit is the same as glide?
If, for instance, I put a sample & hold fed by white noise through the lag circuit, the output voltages would glide from step to step smoothly, instead the abrupt random stepping one usually gets with s/h?

C

[mosc]

Inverting attenuators are great for CV inputs to filters, especially ones controlled by envelops. This gives one knob control so the envelop with open the filter or close it. Both effects are useful.

[fonik]

[Coriolis]

To Mosc and fonik:
Keeewl!

I like these simple little things that make a huge difference...

C

[bearblock]

hey fonik, i was considering stripboarding a couple of the first schematic you posted (the buzzclick one) but sadly enough i can't work out if the offset is +/- or just +, in which case i would probably want to alter things so you can subtract as well as add.

t

[kkissinger]

[mosc]

Have you tried software scopes:

Wave Tools http://www.sonicspot.com/wavetools/wavetools.html

or maybe

Virtual Analyzer http://hacca.altervista.org/

[piedwagtail]

My preference....
Robert

---

pict1394.jpg
Description:
Filesize:	451.17 KB
Viewed:	224 Time(s)
This image has been reduced to fit the page. Click on it to enlarge.

---

[kkissinger]

Never have tried software scopes. Looks very promising... I will take a look.

[fonik]

[Coriolis]

Mucho thanks, fonik! Looks very handy and easy to build.
Now i just need to build some more modules, so i have something to lag, offset and invert! Sofar only 1 vco and 1 lfo is done...

C

[fonik]

i just want to say, that in case you want to use the processor for 1V/oct CVs, R4 should be matched with R3/T1 and P1 to have the OPA at 1:1 amplification - mmmh, am i right or just a little bit confused?