[Pulse wave with no DC]/4066

[Harry Bissell]

Sure, you can use 4051/4066 if you locate them at the summing junction of an
op-amp (after the input resistors), and bias the Ground pin at -0.7V. If the
switch is on, the voltage across the switch is set by the ratio of the on
resistance and the input resistor, and if it is off the input resistor limits
the current to the input pin (diodes conduct) who cares.
The Prophet V did it this way.

harrybissell at netscape.net


jorgen.bergfors at idg.se wrote:
Hi synthesists.

Yesterday evening I tested a little circuit that cancels the DC component that
you get when you modulate the pulse width on a VCO. Roman Sowa came up with
the excellent idea to just add the CV to the output.

I added an extra op-amp after the comparator that generates the pulse wave. A
62k resistor goes from the comparator output to the inverting input. A 22k
feedback resistor from output to inveriing input
A 22k resistor from non-inverting input to ground.
A 22k resistor from PW CV to inverting input. A 1k resistor from output to
output jack, as usual.

Now the wave will be automatically shifted to cancel the DC. You also have the
added bonus that the signal level vill be reduced to 10V p-p without passive
voltage divider.

A gotcha with this circuit is that you can't use 4066/4051 for waveform
selection anymore. This is because the peaks now can go between -10 and + 10
volts.

Happy soldering
/Jorgen


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