UAF42 how does it do in real live?

[patchell]

    The last time I used any of the UAF parts from burr brown was in 1979 (8
pole butterworth band pass filter design, used 4 of the suckers).  I can't
remember which one was which, but one of the modules literally had uA741's
inside it.  It was useful only below about 2KHz or so.  The other module I used
was usedful up to about 100KHz.  However, as I remember, the noise floor of the
entire filter was about 80dB down from 1Vrms (not really great S/N).  My memory
tells me that the part numbers I used were UAF11 and UAF21, but that was a long
time ago, my memory is not good.  I would hope that the newer modules had much
nicer amplifiers in them now.

    Also, if I remember correctly, on the filter module you needed two external
resistors to set the frequency, and one to set the Q.

    Now, if signal to noise ratio is important, and you need to only do simple
filters (two poles), I would recomend different filter structures.  State
variable filters are a lot noisier because they have more amplifiers (3).  A
sallen & key filter will probably do you and uses only one amplifier.  I would
use something like an OP275 for the gain element.

    Just my opion.

    -Jim

Theo wrote:

> Just considering it as a option .
> Need a fixed filter behind a 20bit audio range ADC.
> BB said I should take a look at it, found it rather pricy indeed.
> How well are the opamps? better than 072 I hope?
> If it only saves 2 caps on the print, its not worth $15 to me.
> If the amps are really!! good I might consider it for an other (more high
> end) project comming up next year.
>
> It comes with a filter disign program (handy as I confessed earlyer: my math
> is crap).
> Did not get the full documentation yet, but the program turned out to be a
> universal tool not just UAF42.
>
> Cheers Theo
>
> ----- Original Message -----
> From: patchell <patchell at teletrac.com>
> To: Theo <t.hogers at home.nl>
> Cc: <synth-diy at node12b53.a2000.nl>
> Sent: Saturday, April 01, 2000 4:29 AM
> Subject: Re: UAF42 how does it do in real live?
>
> >     That all depends, what do you want to use it for?
> >
> >     At $15 each, this is a pretty pricey item for what you get.  It is
> > just a simple state variable filter as I recall, you would be better off
> > using a pair of TL072's and some polystyrene capacitors and some 1%
> > resistors.  That way, you can do the same function for about $1.50.
> >
> >     -Jim
> >
> >
> > -----------------------------------------------------------------
> > Visit:http://www.silcom.com/~patchell/
> > -----------------------------------------------------------------
> >
> >
> >

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