[sdiy] Simple EGs and VCAs?

[Scott Gravenhorst]

There are FET and MOSFET VCAs if you're into that kind of thing.  Not perfect
for sure.

harrybissell <harrybissell at prodigy.net> wrote:
>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
>> >
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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