2040

[Kimmo Koli]

On Fri, 3 Apr 1998, Mikko Helin wrote:

> Joachim wrote:
> >First of all, thanks to Juergen for a wonderful 2040 schematic.
> >(http://www.synthfool.com/diy/jh2040.gif)
> 
> Would it be possible to use that schematic to make a "real"
> 2040 clone, an IC with the same pinout as 2040 (not the VCF but 
> just the gain stages)? How much does it cost today to start a 
> production of IC's? Would it solve the Vbe matching problem, too?
> 
Well, when I have 5000-10000$ extra money and a lot of extra time, I'll
spend it in fabricating my own chip prototype. Whit that money I'll get 10
or 20 chips of which typically 90% work if I have no made any design
errors myself. But then I would not design a 2040 clone but a whole synth
with 2-3 VCOs, ring-mod, 1-2 VCFs, 1-2 VCAs, 2LFOs, 3 ADSRs and a
patch-matrix. I would not make any uP control, though. That's somebody
else's job (programming is boring...). And yes, Vbe matching would be
solved, it only a matter of chip area and carefully done symmetrical
layout. 

But I was thinking about an alternative 2040 clone. As quite a lot of the
nonidealities in the 2040 OTA are due to the unsymmetrical output voltage
swing so why make a VCF out of four 3080s or two 13600s and add a diode
clipping circuit to one (or maybe to several) of the OTA outputs. This
diode clipper should clip voltages below -0.5 V or so. Alternatively, this
clipping level would be  adjusted with a potentiometer. What would be
nicer than to control the level of 2040 chacter :-)

Unfortunately I have no time to experiment on that now, but I'll bet
there is somebody there has both a 2040 VCF (or the nice 2040-clone by JH)
and a 4-stage 3080 filter to experiment and compare.  So if somebody tries
that let me know! 

Best regards,
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   Kimmo Koli                         Helsinki University of Technology 
   kimmo at ecdl.hut.fi                  Electronic Circuit Design Laboratory
   http://www.ecdl.hut.fi/~kimmo      P.O.Box 3000
   Tel:  +358 9 451 2273              FIN-02015 HUT
   Fax:  +358 9 451 2269              Finland 
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