vcf5t update

[Magnus Danielson]

Hi!

> A "real" filter with only 3 transistors??? One of our members
> asked me to see if  I could get this filter to work in his current
> project. Well...I wasn't successful doing exactly what he
> wanted ..but I  did something even better (for the rest of us
> anyway).... I removed the opamp all together! Instead using
> a pair of inverting transistor amps.
>
> The coolest thing is it works soooo much better!! That kill
> the neighbors dog , split the sky oscillation is gone. The
> cutoff response is very smooth. You can easily sneak up
> on the res advancing to full on without fear you are about
> to blow your speakers and when it does self oscillate it's
> even (more or less) across the entire res sweep.
>
> The update is here. You guys should build one today!
>
> http://www.xavax.com/efm/cbook/pics/vcf5t-sd.gif

Now I finally taken a look at this filter, and I must say that I must really
take a closer look. First it looks a bit corny, but for instance the
integrated expo converter and adjustable transconductance looks nice.
One of the interesting things here is that it is basically off the shelf
components for basically anyone. I think it is interesting also from the
point of view of power consumption, you should have no trouble at all powering
this from a 6R22 9V battery.

Component list:
100	1
470	2
1k	2
10k	6
22k	2
47k	1
100k	3
330k	2
470k	3
10k POT	1
50k POT	1
50kTRIM 1
1nF	1
10nF	3
100nF	2
10uF	1
33uF	1
1N914	4
2N3904	2
2N3906	1

Doesn't look too excessive, does it?

Hm... better heat up that soldering iron I guess ;)

PS. Tom, shouldn't you *really* learn to write 10n and 1n instead of .01 and
    .001?

Cheers,
Magnus