[sdiy] Re: OTA comparisons, VCA shootout

[Metrophage]

--- "JH." <jhaible at debitel.net> wrote:

> Often, just a bare naked transistor pair is all you need, as this 
> performs the multiplying function in any OTA; the rest is just
> for interfacing. Like, giving the control current input a different
> direction, and making a single ended output with high common 
> mode voltage range for your output current. If you get rid of 
> these in your design, you will have a less comfortable sulution
> (i.e. you will have to put some days of work into a design of the
> best interfacing for your application), but you will also get rid of 
> sources for errors, such as bad current mirror precision and CV 
> feedthru that may come from this.
 
> For synth-diy, the fun is in designing circuits instead of just using
> combinations of IC application notes, isn't it? So the fun will be 
> increasing, at least as long as we can buy matched transistor pairs.

I agree, although people have been hand-matching them with some
success, and less expensively. The Japanese matched pairs appear to
perform well.

I imagine that designing circuits is more fun, but I don't really know.
My start was finding schematics to vintage gear which I was not able to
find, nor afford to buy. After a while I began to find info from
current DIY people (such as your excellent web pages!). I began with
the goal of simply building a decent modular and some drum circuits,
but as time goes on, and I see my bench and the components I have
bought, it occurs to me often that I could learn to do so much more.
When I began I thought I'd build a synth first and learn about
electronics later as a secondary goal. Maybe I have been too
intimidated or lazy, but lately the idea of putting off learning
electronics seems foolish. Otherwise I probably build a modular which
has mismatched modules and other problems, and I'll just need to
overhaul it later anyway.

What perplexes me the most now is not understanding that there is a lot
which I don't know, but trying to figure out what it is exactly which I
need to learn! For example, I can look at diagrams of dozens of VCAs,
and understand on a very crude level how they are supposed to work. I
guess I mean that I understand the modules purely on a musical/sonic
level (so much as I can), but not on an electronic level. For example,
what do I need to know about how a VCA works which would enable me to
build one? These are fundamental questions which no amount of
schematics-gazing can answer.

CJ

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