[sdiy] 4069 / 4049 VCA

[harry]

Here's what I recall...

The 4049 vca originated from Popular Electronics some time (ages) ago.
The connection uses only one transistor of each inverter pair...

All 4049 are UB... there is no buffered version.

The input diodes are different in a 4049, there is no diode to the
positive
rail. The 4069 has these diodes and will not work when you ground the
positive
rail.

BTW I've done a little simulation of the 4069 VCO... I think you can
capacitivly
couple a pulse from the "middle" of the schmitt trigger and cancel the
reset spike
to a great extent. What I can't simulate is does it screw up the tuning
?

I'll send you (Scott) a schematic of this later if you want to try it on
your setup.
It may add enough complexity to make the thing not as attractive...

You also may not be able to haer the difference.

H^) harry

Scott Gravenhorst wrote:

> I have a copy of a schematic from TomG's cookbook portraying
> a hex VCA made from a 4049.  Unfortunately, it is labeled simply
> '4049'.  I am assuming that it is the UB part because it runs in
> linear mode.
>
> I learned (right here!) that the 4049UB does not employ symmetrical
> transistors as the 4069UB does.
>
> Because of the asymmetry, I assume I would have to adjust some
> resistor values (and also the pinout) so that I can use the 4069UB.
>
> A couple of questions:
>
> 1) Does the asymmetry of the 4049ub actually provide a benefit?
>    (I do realise the original intent was that the 4049 would
>    do CMOS to TTL/DTL conversion).  My question refers to a
>    benefit that might be realised in the VCA application.
>
> .. if not,
>
> 2) Has anyone already designed a 4069UB based VCA (so I don't
>    need to figure out why a wheel has to be round again) ?
>
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