AW: Sines breaking down (was: AW: 35 - the next step)

[Haible Juergen]

	>Yes....all transistor versions so far...? I though today...maybe I
heard it
	>somewhere...5 transistors instead of 3....? Did you say that?
Sometimes
	>people tell me things and I don't hear it until it becomes my
	>idea....(that's what my wife sez!) I'll probably try it tonight...
be nice
	>if it works. There is a fet example also, might switch to 3819s
...if it
	>fixes it. The example is for a 4007 but if you have to go to two
ics, why
	>bother? The dual otas are cheap. (I might try it for fun though) 
	>
	>-tg

You're right of course, the dual OTA solution is the most straight forward
one.
My whole interest in this "pre-historic" stuff is that after having so many
"almost perfect" filters it's great fun to explore the strange oddities as
well.
There was a time when I dreamed of a "real Moog filter" I would turn up my
nose at a diode ladder. Since I have all the "most desirable ones", my
interest has changed completely. (I'm sure you know what I mean, as
you have built so many different modules yourself.)

The great surprise is that the "obscure" stuff isn't that inferior to our
"dream filters" as I used to think. I have hooked up the 3-transistor-VCF
to my modular system a few days ago, controlled by a sequencer and
sync'd to the OB-8's arpeggiator, and recorded a track with that
configuration
last night. The filter makes a really nice bass, not at all "thin" and
"nasal"
sounding as the MS-20 is sometimes described. (Not nessesarily my opinion !)
The input level was much higher than it normally would be in a MS-20, so
high
that playing intervalls others than octaves, 4ths and 5ths between the two
VCOs running thru the same filter would sound dissonant. But the way
I used it, it makes an impressive bass.

Nevertheless I can only think of one application where this minimal version
really would make sense, and that's a full polyphonic synth. One opamp
and 3 transistors are very tempting when you are going to build 49 of these
circuits (;->). (No, I'm not going to, just dreaming of ! But as dreaming is
not expensive, I'd rather dream of 6 transistors and a dual opamp per voice
...
and probably two thyristors as well.)

JH.