Adding CV to a 4016 OSC? Is there a rule of thumb?

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Darfiss
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Adding CV to a 4016 OSC? Is there a rule of thumb?

Post by Darfiss » Wed Nov 27, 2019 8:33 am

Hey guys,

so im pretty new to DIY Modulars and i've build a six voices OSC with a 40106, including a passiv mixer.

And it acutaly works fine (my first active module that does something!)

Now next on my list ist adding an active mixer (researching virtual erth mixer's at the moment for that)

And adding CV.

I want my modules to be compatible with the doepfer standart and looked on the doepfer side for informations. But i couldnt find anything regarding values of CV.

I have a Behringer Neutron and the CV values are mostly in the range of 5-6Volts or way lower.

When i build a module, that has a max 12V CV out, wouldt it blow stuff up?

I thought about building CV with vactrols and made my own Vactrols using LDR's, LED's and shrinkingtube, but its hard to find the right resistors for the LED's.
I experimented with the LFO out of the Neutron (if i remember correctly LFO CV out was around 2 Volts...) and the LED responded to slow or to hard.

Should i actualy use resistors for the vactrols? How to handle the difference between the 2V CV OUT from the LFO and a potential module that outputs 12V CV?!

How do you implement CV into your modules? Opamps?

Im pretty new to all of this and i tried searching forum, but couldnt find satisfying answers.

Maybe someone can point me in the right directions?

Thx

jorg
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Post by jorg » Wed Nov 27, 2019 9:17 am

Euro CV is most commonly in the range 0 to +5V; -5V to +5V is almost as common. You could probably safely go as high as +8V; I wouldn't recommend any higher than that.

Like any diode, LEDs have a threshold voltage and below that voltage, almost no current is conducted (and no light emitted). The threshold depends on color; red is ~1.2V; blue is ~3-4V. Above the threshold, it's very nonlinear. You must always use a current limiting resistor (or a fancier, current-source driver circuit). To approximate linear operation (such as for a vactrol) you need to drive with a fairly high voltage and reasonable resistor (a few volts and a few kilohms). 2V is not enough for this job.

Most modules have op amps at their inputs to mix and scale the CVs.

nrrrd
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Post by nrrrd » Wed Nov 27, 2019 10:47 am

For a 40106 oscillator you can use a NPN transistor to control the pitch in a linear way, via CV, or a NPN and PNP transistor to control the pitch in a exponential way. It will produce a click pulse and a sawtooth.

I've got a circuit that uses a 40106 and TL074 opamp to produce two oscillators with a square wave and sawtooth. There is also the possibility of PWM and it runs off a single sided supply (0 to 12v, but 0 to 9v or 0 to 15v would also work).

I've only simulated it in LT Spice so far, but I'm confident it will work. I'll post the schematics / Spice scheme when I get home.

Darfiss
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Post by Darfiss » Wed Nov 27, 2019 1:07 pm

Thanks for your replys, the CV thing helped a lot, guess I finally have to figure opamps out...

@nrrrd thanks for the tip with the transistors! Can't wait looking into your schematic

nrrrd
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Post by nrrrd » Wed Nov 27, 2019 2:50 pm

Here's the schematic.
The oscillator section is based on this, by user Synthmonger on electro-music forum:
http://electro-music.com/forum/topic-28799.html

The 1v/oct section is based on the 4069 VCO by Rene Schmitz, adapted by me to single sided supply:
https://www.schmitzbits.de/vco4069.html

Feeding the saw back into a spare 40106 inverter - I thought of that all by myself :)

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Post by guest » Fri Nov 29, 2019 1:53 pm

you might want to switch your opamp to a noninverting configuration, that way you dont have the current leakage through the 220k, which will effect your tuning. the opamp will probably have to be a rail to rail type.
openmusiclabs.com

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