40106 12-Voice Oscillator

[Kinski]

I suck at schematics and layouts. However, I attempted to make 12 independent oscillators using two 40106 ICs.

Can someone here take a look at this and see if anything seems wrong? I'd greatly appreciate it!

[Freppo]

Hi kinski,

Cool, but why 12 oscillators? More than 3, tops 4 oscillators is pointless and will not add much to the sound imho.
Insted you could use a few of the inverters for other functions, such as PWM or buffers.

You need 1 more resistor (R1) for each oscillator, to set the max frequency.
Otherwise the pot will kill the oscillation in the end and the sweep of the pot would be very uneven.
R1 could be place on either side of the frequency pot.

You can't replace the resistors with pots either directly for mix control.
Another resistor (R3) for each oscillator would be required to stop the oscillators from potentially getting mixed directly which would stop the oscillators from working.
This resistor can also be placed on either side of the mix pot and should be at least 10K.



It works much better with fixed mix resistors and switches to kill engage/disengage each IMO.
The switch would have to be placed to take the frequency pot out of the circuit and terminating the oscillator, insted of just disconnecting the output of the oscillator.
That would still leave the oscillator to affect the other oscillators that share the same powersupply.



It's a good idea to buffer the mixed output from the oscillators aswell through a CD40106 gate and have some DC filtering to stabilize the oscillators. I would use a 100uF and a 100nF between V+ and ground.

I hope that helps. :)
/ Fredrik

PS. I'm writing an article on CMOS oscillators that I will share on my blog in a few days.

[Kinski]

Freppo! Thanks for your input!

My thought was that Id just like to have 12 independent voices. Why would that be an issue? Would you not be able to hear each individually? Also, I'd have on/off switches for each voice, and I'd probably not have all of them on at the same time. I figured I would tune them in groups of 4 bass, 4 tenor, 4 soprano. Like a weird choir. Would this not work?

Also, I guess I'd make the mixing resistors of different values for the three range groups, as the basses would certainly be much quieter than the sopranos otherwise.

For the layout, I can add the filtering caps, and add the range limiting resistors to the pots. Would putting them on lugs 1 & 2 work?

I no nothing of 40106 gates. What would the benefit be?

Also, I would be able to run the OUT of the board into a simple low pass tone control and then to a master volume, then to outback or internal speaker, yeah?

Thanks again!

[Freppo]

12 independent voices is a cool idea in theory as you discribe it, but my experience tells me that mixing more than 3-4 oscillators and it becomes a mess.

You should breadboard and experiment your ideas. To start off with a vero isn't very practical imho.
The range limit resistors would have to be put to or from each pot. It won't work on lug 1-2.

Yes, a CD40106 can drive a small speaker. If mixning several signals you will probably end up with a too weak signal if it's not buffered or amplified first.

Have a lookout for part 4 of my CMOS series here. It will cover a few fun ways to use logic gates. :)

/ Fredrik

[Travis]

If you used buttons for the on off switches couldn't you theoretically tune it to range over a full octave and use it as a keyboard/synth?

[Kinski]

Yep! I was thinking about doing that. It would be polyphonic too, which is nice. More often I see a keyboard synth using just one oscillator so it would only be monophonic.

I'm gonna breadboard this in the next few weeks when I have more time and see what comes of it.
I've been listening to too much Eliane Radigue recently. Got me hooked on oscillators and drones.

[tabbycat]

i've got this on my list of to-trys for when i get around to modding my monotron, but might be of interest to you. the resistor ladder on rotary switch or diy keys.

http://picsynth.000space.com/monotron/keyboard.html?ckattempt=1

by way of expressing a personal reservation, i think it would be defeating the object to make it all tuned. if you are chasing low-fi tuned you may as well buy a disposable casio. no point in breaking into a sweat to reinvent a cheap wheel.

but you could have half the oscillators tuned and half on pots, to get all the shades inbetween.
those dark dissonances and cross-interfering frequencies are the sweet spots as far as i'm concerned. though that's my preference and maybe not what you are after. but if you like radigue, am guessing it may be. she's hot.

also worth considering ribbon resistors.

[Kinski]

Thanks tabbycat!