[sdiy] UAF42

[Scott Stites]

Hi Scott,

Good points, indeed.  I have to agree with Phillip, though, for Vactrol hounds like me, it would make a pretty compact little SVF (haven't calculated it yet, but I think the 1000 pF caps in that case would be fine).  Of course, the matching of the Vactrols would obliterate the spec on the caps =-D.

An exponential current sink to drive the Vactrols would take a couple of transistors, and, while I'm at it, hang a Vactrol off of pin 3 and get VC resonance.  

Now that Rene Schmitz 4007 design......I'll definitely have to try that, too!

Cheers,
Scott

-----Original Message-----
From: Scott Gravenhorst <music.maker at gte.net>
Sent: Feb 24, 2004 12:37 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Cool chip alert

Wow, I thought it was a wanked design as well.

The other URLs pointing to clever usage of this were OK, but I think
there's something seriously wrong with using external OTAs to allow
voltage control of something like this.  The integrators on the chip
should have been made of OTAs, not opamps, IMHO.  That would have been
far more useful than what they did.  After all, a SVF - VOLTAGE
CONTROLLED, can be made out of a single dual OTA IC.  And if I want to
mess with unusual designs, I'll happily build the René Schmitz 4007 VC
state variable filter.  I fail to see anything superior about this IC
other than the matched 1000pf caps (which are too large IMHO and you're
stuck with them).  And I think that there are ways we can match caps to
make a better OTA based VC-SVF.

Just my $.02 worth of pure opinion.











Colin Hinz <asfi at eol.ca> wrote:
>On Mon, 23 Feb 2004, Tim Escobedo wrote:
>
>> http://www.speakjet.com
>>
>> Might be useful for sone nice effects.
>
>Who are these people? And why did they let such a wanker design their
>website?
>
>Okay, I don't really expect an answer to the second question, though
>neither of their news items display anything except the headline.
>Oh well, I'm sure they've got a very good reason for doing it
>this way.
>
>The company's main website is much closer to being wank-free, luckily:
>
>http://www.magnevation.com/
>
>I do wonder what's in the guts of the SpeakJet -- it's not like a
>few guys working in an industrial park in Alabama can suddenly
>build a fab to start churning out mixed-signal ASICs..........and
>as they're really clear about providing an entirely American-made
>product (and I don't have any problem with "buy domestic" campaigns,
>as we could use a bit of that up here), so that implies a fab in
>the USA.
>
>Looks like quite an interesting chip. If I thought there'd be any
>chance I'd get around to doing something with them in my lifetime,
>I'd buy a few. But first I'd better build something permanent
>with my pair of SN76477s......
>
>- Colin Hinz
>  Toronto, Canada
>
>

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