[sdiy] Analog Computers, Rocket City

[Scott Nordlund]

As state variable filters go, it's actually pretty weak sounding.

> From: don at till.com
> Date: Sun, 27 Jan 2013 09:49:46 -0800
> To: lanterma at ece.gatech.edu
> CC: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Analog Computers, Rocket City
>
>
> On Jan 26, 2013, at 9:02 PM, "Lanterman, Aaron" <lanterma at ece.gatech.edu> wrote:
>
>> The EML 101 design has an analog computer-ish feel to it. The VCF has a weird integrator structure that uses two capacitors per integrator. Someone -- Harry Bissell, maybe? I can't remember now -- mentioned that was a design that showed up in old-school analog computers.
>
>
> I'm intrigued... here's the schematic:
>
>     http://www.synfo.nl/servicemanuals/EML/EML-101_SCHEMATICS.pdf
>
> I've always known the differential integrator as a classic opamp circuit, 'never heard about it used in analog computers before.
>
> So in this circuit they're taking the balanced outputs of the transconductance pairs and sending them to differential integrator inputs.  That seems elegant.
>
> But not really.
>
> The input impedances of the differential integrator are wildly different, and the positive input voltage is seen on the negative input.
>
> (And this is probably why I haven't seen it used in analog computing.  You'd have to buffer each input first.)
>
> So in this case the differential integrators will place some weird loads on the transconductance pairs, probably creating some unique nonlinearities.  But hey, maybe it sounds good.
>
>   -- Don
>
> --
> Don Tillman
> Palo Alto, California
> don at till.com
> http://www.till.com
>
>
>
>
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