[sdiy] Simple EGs and VCAs?

[harrybissell]

Hell... send him to Jorgen Bergfors site for the "VCA Shootout" which
has about every simple VCA known.  Granted, you could do the one transistor
current source and it would be easier.  (google search "Bergfortron")

JH has a Roland clone (think its roland but maybe korg) on his site... two
transistors
and an opamp follower. Not too good on high level signals.

Old "diode keyer" are very simple as well (and don't perform too well either)

or how about (dast I say it ???)

~vactrols~   :^P

H^) harry

Peter Grenader wrote:

> World's easiest VCA, using a 3080 or 13700, call this IC 1:
>
> 1) Audio input through a small value current limiting resistor (like a 330
> ohm)  then into the + input of IC 1
> 2) Trim pot from +/- VCC into negative input of IC 1. Put a current limiter
> of some sort off the wiper of the pot which leads into the - input.
> Something like a 1K
> 3) IC 1 output  to some sort of non-inverting buffer (a voltage follower
> being the easiest).
> .4) output of buffer through a 1k resistor to the faceplate (VCA out)
>
> 5) PNP tranny with base to ground - emitter goes to VC input through a
> current limit resistor.  You can use this as a summing node, putting an
> offset pot in there as well if you wish.  Collector of PNP through another
> current limiting resistor, then into the CONTROl input of either the 3080 ot
> 13700. It's pin 5 on the 3080.
>
> There u have it.  You may have to slap a pulldown resistors on the output of
> IC 1 leading to the buffer and on both the + and - inputs of IC1.
>
> If it doesn't work at first, start twiddling the trim pot until you reach
> the sweet spot.
>
> A voltage follower is an op amp in which the signal goes into the + input,
> comes out the output of the op amp with the - input is shorted to the output
> as well.
>
> A pulldown is a resistor in which one end goes to ground, the other to the
> line it needs to hold down.
>
> A current limiter is a reistor inline with the signal flow.  One end goes to
> what is being connected, the other end goes to what that is being connected
> to.
>
> hope this helps.
>
> - P
>
>
> Cole Groff wrote:
>
> > Hey guys,
> >
> > I was curious if there are simple beginner EG and VCA designs out
> > there, that I could build.
> >
> > I'm just getting into the DIY business.  Built a Ken Stone VCO!  Not
> > all by myself, but it works.
> >
> > Thanks guys,
> > Cole
> >