[sdiy] Simple EGs and VCAs?

[Peter Grenader]

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
>