[sdiy] OTA VCA

[cheater00 cheater00]

Exponential is curved, linear is straight lines. Look on google images for
exponential envelope. Look at your CV on an oscilloscope. If you don't have
one, get one, it's an important tool.

Just doing the rail might be enough... with the added bonus that if the
rail you use is very weak, additional notes will make the total a bit
quieter by making that rail sag. But then don't use that rail for anything
else.

You shouldn't feel like a hack. You're doing great work!

On Mon, 20 Mar 2017 21:13 Elain Klopke, <functionofform at gmail.com> wrote:

> Hey guys,
>
> Thanks!
>
> Cheater: I have no idea what linear vs. exponential looks like unless the
> description tells me so, lol. I'm such a hack and constantly grabbing a
> piece of this or that circuit to suit my needs....
>
> Tom: I had initially trimmed it down to the schmidt trigger, diodes, pots,
> capacitor, and the buffering op-amp. I'm guessing that the buffer isn't
> really needed since one AR generator is going to one VCA, but shouldn't I
> keep the schmidt trigger there to give the envelope a nice 0-5 volt gate
> pulse when the key is pressed? Or is just a five volt rail getting
> connected through the key to the diodes enough?
>
> Dave: Thank you, I'm glad there's no real distinction between them. I
> should probably get a few extras for some VCFs or something.
>
> -Ian
>
> On Mon, Mar 20, 2017 at 2:20 PM, Dave Magnuson <abide at dmdrafting.com>
> wrote:
>
>
>
>
>
> On Mon, 20 Mar 2017 16:58 Elain Klopke, <functionofform at gmail.com> wrote:
>
> So I'm going to put this can of worms on the table and back off slowly
> before opening it....
>
>
>
> Due to various reasons (not the least of which was getting shafted by the
> person  I purchased a large quantity of LDRs from) I'm switching over to an
> AR envelope generator and VCA combo for keying my notes on the paraphonic
> synth.
>
> I decided to go with some circuits that I know and have assembled a few
> times, the AR generator and VCA from Ray Wilson's original Sound Lab mini
> synth. I'm going to try to trim away the bits of the AR generator that have
> to do with the triggered mode since these are going to be gated by the key
> presses only and see if they still work.
>
> Question time: Ray's VCA is a simple half-a-LM13700 with the CV going into
> the Bias input and the op amp bit doing its amplify-y thing.
>
>
>
> 1) In his notes, Ray talks about the response to the CV being linear.
> Since I'm just using this to switch the notes to the rest of the synth with
> a little preset attack and release that shouldn't be a problem, right? It
> would only do strange things if I tried feeding it an exponential envelope
> from an external source?
>
>
>
> 2) If I hard-wire the initial gain "knob" to no initial gain, it's going
> to be silent until the envelope hits it?
>
>
>
> 3) Is there any noticeable difference between an LM13700, NJM13700, and
> NJM13600 besides the price? Because at 148 chips for a 3-octave keyboard,
> price is kinda a thing.
>
>
>
> -Ian
>
> _______________________________________________
>
>
>
>
>
> Hi Ian
>
>
>
> I have used the NJM13600 and NJM13700 almost exclusively and have had no
> problems in any of the circuits I’ve tried.   I have little experience with
> “real” LM13xxx however….
>
>
>
> Dave M
>
>
>
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>
>
>
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