Doing it all in 4069s (Was: Re: [sdiy] New Vco (new images))

[Jon Darby]

Good afternoon,
    This fascinting topic has come up right as I am brainstorming about how
to use the 4069 as a VCA for the volume side of my
4069-plus-a-few-caps-and-resistors theremin. I am using two 4069s, one for
the reference oscillator, and one for the variable oscillator, and have two
sections of the reference 4069 free. Is there anything I can use these
unused sections for? If I could use them as a VCA to control the volume of
the mixer circuit I could keep my parts count down and I won't feel so
guilty for tying those pins down to ground, but I know precious little about
VCAs, grrr. Any help is tremendously appreciated!

Your pal,
Jon Darby

----- Original Message -----
From: "Magnus Danielson" <cfmd at swipnet.se>
To: <efm3 at mediaone.net>
Cc: <synth-diy at dropmix.xs4all.nl>; <uzs159 at uni-bonn.de>
Sent: Saturday, September 29, 2001 10:05 AM
Subject: Doing it all in 4069s (Was: Re: [sdiy] New Vco (new images))


> From: "tomg at efm" <efm3 at mediaone.net>
> Subject: Re: [sdiy] New Vco (new images)
> Date: Sat, 29 Sep 2001 04:26:45 -0400
>
> > Thanks Rene. Using a 4069 was a great idea. It really does
> > make a terrific little vco. I played with it some more and put
> > it here...
> > http://people.atl.mediaone.net/efm3/vco-4069.pdf
> >
> > This version has an extended lower range 0.23Hz to 18KHz
> > with a very slow ramp. It's scaled as high as I can hear. The
> > last octave I can make out runs from about 5K to 9.5K. I
> > think I can hear that the 9.5K to 17.5K octave is also correct
> > but I'm more than likely fooling myself. Not that it's correct
> > but that I can hear it...;-)  I'm pretty sure it's ok.
> >
> > Yes it uses a tempco but they are pretty cheap these days at
> > $2.50ea...Anyway thanks again this was great fun.
>
> Hmm interesting!
>
> This kind of rings a bell in me, I've actually considered the oddball
> idea of building a synthesizer with 4069s as the only active
> component.
>
> A 4069 is basically a high gain inverting amplifier. If you look at
> the above VCO, you should be able to remove the TL072 by using two
> more of the 4069s inverters. Just think of it, it is indeed possible
> even if it requires some more thougth.
>
> As for my idea, naturally the exp-transistors can't be avoided.
>
> As for the filter, there is the JHs WASP clone, but I do wonder if not
> the CA3080s could be replaced by 4069s if given thought.
>
> VCAs is not problem, a 4069 and 12 1MOhm resistors and there is 6 VCAs
> all prewired together to form a mix. Then for the virtual ground
> summer completion a single 4069 inverter for the buffering.
>
> For signal and CV summers will single 4069 gates do just fine.
>
> I think it should be possible to do an envelope generator too.
>
> I don't think it will be a high precission synth, but I am quite sure
> that one could make one that actually works. I'd like to dub this
> synth to 4069.
>
> There is surely a few problems in doing this, but I think those
> problems are there to be found and lessons to be learnt.
>
> It is strange what a brain can produce after just getting out of a
> hang-over ;O)
>
> Actually, I think I'll start scetch some on this right away... ;O)
> Any takers?
>
> Cheers,
> Magnus