[sdiy] Comparator = Opamp ??

[harry]

The 4049s  (or maybe 4069UB ?) are inverters... not comparators. I found
this config to be ill-behaved as a linear amp... BUT you are dead right that
is the feature in the Wasp.

Replace those inverters with anything else (opamp, fet and opamp...) and
you have every State Variable Filter ever made (My Aries AR-314 would be
one...)

You could tandem two filters... but the design is past me if you try to use
one big feedback loop...  but two in series like the MS-20 config is easy.

Post it when you get it... I'd like to see

H^) harry

Rob wrote:

> Well, didn't the Wasp filter kinda do that? I mean, by using 4069UBs to act
> as opamps?
>
> BTW, anyone ever build the Wasp filter with opamps instead of 4069s? Just
> wondering what effect is has.. BTW, I am actually thinking about redesigning
> your wasp filter but adding another two filter stages for a switchable
> 2pole/4pole config. Don't know if I will do it yet, but I might give it a
> shot..
>
> I realize that a good portion of the unique sound of the 4069ubs is what the
> Wasp filter is all about, otherwise it seems to be a simple OTA based
> filter. I am just curious what kind of mucking up could be had by
> mixing/matching opamps and 4069s in a configuration like that and make it
> switchable perhaps.
>
> Rob
>
> ----- Original Message -----
> From: "jh." <jhaible at t-online.de>
> To: <peter83 at bigfoot.com>; <synth-diy at node12b53.a2000.nl>
> Sent: Tuesday, March 06, 2001 5:43 PM
> Subject: Re: [sdiy] Comparator = Opamp ??
>
> > > A comparator is a digital device that outputs a 'high' signal (logic 1
> or
> > about 4 to 5 Volts), when the voltage on the + connector is higher than
> the
> > voltage on the - connector. If the one on the + is lower, it outputs a
> 'low'
> > signal (logic 0 or 0 Volts).
> > >
> > > An Opamp has exactly the same appearance in schematics, though i get the
> > impression (from Circuit Maker 2000 (simulation software)) that it behaves
> > differently. Can anyone tell me the difference, or state that they infact
> > ARE the same...
> >
> >
> > Things have evolved quite a bit since the start, so you have a lot of very
> > specialized
> > devices, both for opamps and comparators. But in the beginning, a
> comparator
> > was just an opamp without the compensation capacitor - no dominant pole,
> no
> > closed loop stability, but much faster than an opamp.
> >
> > I think I've seen one circuit from Electro Harmonix (the masters of cheap
> > design, in any positive sense of the word), where one comparator of a
> > quad package is abused as a linear opamp - quite some feedback network to
> > get
> > it stable, but avoids an extra DIL package for opamps when one comparator
> > was unused. Not that such things would be wise nowadays when capacitors
> > are more expensive than opamps ...
> >
> > JH.
> >
> >