[sdiy] Design Patterns

[Darren Reid]

Hi!

>    I need to find the design pattern for a simple VC 2 channel mixer
>    right now...three stages of those solves my curved response 4-way
>    mixer design in a hurry....
>
> Umm, like this?
>   http://www.till.com/articles/scanner/index.html


Very interesting. It's along the lines of what I'm working on, but
conceptually it's just slightly different. What I really want is  multiple
cascaded stages of identical 2 channel "VC crossfaders". You feed two inputs
into the first x-fader, then the out of that goes in with the third input
into the #2 x-fader, then the out of that gets mixed with input #4 at the
third x-fader....etc. Actually, I really only need a 4 input device, so that
is where I stop anyway.

All of the x-faders are fed the same CV.

Now, I could maybe adapt your circuit to a cascaded series of 2 channel
mixers, but I don't think that that would be the smoothest way to go about
this. Those diode/resistor chains give sharp cutoffs, and there must be a
silkier way of x-fading two signals, neh?

I'm sure this is an elementary design problem, but I'm a complete novice at
electronics. I *have* prototyped the effect in Reaktor, and it sounds
gorgeous. I was pretty sure it would; it's based on the concept of
"transformer sag" and the transfer curves in tube amps....well, that's where
I got the idea :)

Now, maybe I'm misunderstanding how those chains of resistor and diodes work
in your circuit...maybe that *is* a good way to make a 2 channel x-fader.

So....any ideas on simple 2 channel x-faders out there? I'm sure it's
something simple with 2-4 transistors and a small number of resistors, but
it's just beyond me so far. It's lots of fun to think about, though!

-Darren


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