Env vco!

[Magnus Danielson]

>>>>> "B" == BJ  <zzynt at swipnet.se> writes:

 B> Many years ago needed a VCO with a saw wave,and i
 B> found a way to do this using a 4046 PLL.

BJ, you forgot to put a value on R11. I suggest a 100k.

Also, why don't you let the cursuit take more of all that space?
I try to scale up my schematics when they don't take that much space.

 B> And the MC202 and SH101 envelopgenerator and a simple VCO are found at:
 B> http://home8.swipnet.se/~w-88660/schpcb.htm

For those that wishes to use an exponential cursuit with the 4046 VCO
may hook it in on the current input of pin 12. This input wishes to
see a current being drawn towards ground, so hooking it to the current
output of a standard dual-transistor expo-cursuit (like the ASM-1 for
instance) should go well.

Also, you may still use the VCO input for a real linear input (pin 9).

The 4046 VCO have a typical linearity of about +/- 1 % and a
temperature stability of +/- 0.12% (+/- 1200 ppm) at 5V. The linearity
depends on the resistor to ground from pin 11, it should be at least
10k, put 100k is recommended (for 0.5% linearity). The temperature
dependency drops to +/- 150 ppm when the powersuppy is at 15V.

You could make som strange form of modulation by dribbling with the
inhibit line, and thus pausing the load cycle (it shuts of the
current-mirror). It is not synching, it is just diffrent.

The old CMOS versions of this VCO would scream up to 0.8-2.4 MHz
(depending on powersupply), the newer onces get even higher. So, to
get a pretty good responce one should consider pretty quick op-amps.
The reset time is quite small, but if one would find it a trouble,
then you could allways add the Franco compensation resistor in series
with capacitor.

The upside about using the 4046 as a core for a VCO is that you get
the reset-cursuit for free as well as phase detectors to make PLL
loops, in case you would fancy that game. BJ reused one of those to
make a MS-20 style ringmod.

Oh, be carefull about loading the capacitor, use high-impedance
op-amps (about 1 Tohm). Also, it could be a good idea to feed back the
outputs of the op-amps to form guard rings around the capacitor
terminals. This would eat surface currents, usefull if you want it to
track good at low current (frequency).

 B> Regards
 B> Grommit.

Cheers,
Wallace