CV-In for NAND gate Synth - some questions

BloodMaster · Joined: Jan 28, 2012 Posts: 3 Location: germany

Hello!

I am new here, so let me say hello to all! I read a lot but didn´t post yet. I am musician and using synths a lot. Now during last year I tried around with some electronics and created my first own small synth (4093 NAND based) with 3 OSC and different ways to mix the OSCs, it runs on a 9v Battery. So I understood how that works and I am happy! But now I want to intergrate a cv-in for controlling the pitch of the oscillators by 1. other synths and 2. a step sequencer wich I want to build next.

On the pic you can see my cv-in as it is now. Does that look ok for you (more professionals than me)?

The LED and the LDR sit face to face in a heat shrink tube. The "outputs" on the right go parallel to the resistor that is responsible for the pitch of the nand gate. By the pot I can regulate how strong the effect should be.

It works quite well with audio signals from another NAND-machine (slow squares) and sinewave sounds coming from the soundcard. But will it work in a musical way with cv from a step sequencer? I couldn´t test it yet - no seq.

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Questions:
1. When I want to control 2 OSCs by the cv-in at once I have to use 2 LEDs and 2 LDRs and so, right? I mean just connecting 2 LEDs to the 1 LED driver... Or is there another way?
2. What parts could i use instead of the LED/LDR combination?
3. Is it just my feeling or does the LED/LDR react quite slow on pitch/amplitude changes? What could I use for making it react fast?
4. I know this is a more complex thing but it´s my goal for the future: How can I create a 1v/oct control...? Is that done at the OSCs or is it a thing of the cv-in? Is it possivle with a +9v supply at all?
5. Are there other ways for making a cv-in than using "voltage to resistance"? (In my case the pitch of the OSC is controlled by resistors & capacitors, so this seems to be the solutio for now. But I try to learn, so if there are other ways...)

Would be nice to get some feedback, meanings and discussion with some nice diy guys here.

Thank you!

EdisonRex · Posted: Sat Jan 28, 2012 1:40 pm Post subject:

First,

Bloodmaster, and I hope you find this site continuously useful.

That kind of vactrol control is not very fast, as you can see. You don't say what LED and resistor you're using so it would be hard to comment on linearity or range. But there are better ways to do it, even on a single supply.

A simple JFET voltage controlled resistor circuit will replace what you have, and will have a faster response and will be more linear, and work on a single supply. It might at least make your existing oscillators vary in pitch more reliably.

No doubt others have more ideas.

Uncle Krunkus · Posted: Sat Jan 28, 2012 2:28 pm Post subject:

I would also look into an ADC (Analogue to Digital Converter) chip.
The incoming CV would then be converted into set of binary lines which could be used to divide down a high frequency master clock.
Or, they could be used to control other digital functions. I've been investigating this myself. (with the ADC0801)
It would allow a lot of scope for experimenting.

BloodMaster · Joined: Jan 28, 2012 Posts: 3 Location: germany

Thanks a lot for the replies. Yes, sorry, I use this red LED: http://www.reichelt.de/LEDs-Low-Current/LED-3MM-2MA-RT/index.html?ACTION=3&GROUPID=3020&ARTICLE=21626&SHOW=1&START=0&OFFSET=16&
and this LDR http://www.reichelt.de/Fotodioden-etc-/LDR-07/index.html?ACTION=3&GROUPID=3045&ARTICLE=10208&SHOW=1&START=0&OFFSET=16&

I will have a look at the pdf EdisonRex posted and come back if I have any questions. Thanks so far, if anyone has other ideas, let me know. The ADC stuff looks interesting too but I guess I will follow that eventually later. One step before another Wink