[sdiy] hi shelving filter

[mark s]

thanks magnus.
do you have any experience with the burr-brown UAF-42 universal active 
filter ? thoughts ?

and when you say 'put the ends to a pos & neg input bus' do you mean the 
inv and noninv terminals of an opamp ? can i expect symmetrical HF boost 
and cut this way ?

i take it y'all don't like inductors.

mark

At 09:20 PM 2/13/2004 +0100, you wrote:
>From: mark s <djarum11 at mindspring.com>
>Subject: [sdiy] hi shelving filter
>Date: Fri, 13 Feb 2004 15:16:15 -0500
>Message-ID: <4.2.0.58.20040213143131.0225deb8 at pop.mindspring.com>
>
> > greets list
>
>Hi Mark,
>
> > i am building a mic pre based around the SSM2019.  i would like to add a
> > high shelf filter with cut or boost starting at 3 selectable frequencies.
> > 4k, 8, and 16k.
> >
> > obviously this is for vocals so it's gotta be pristine-clean and the
> > phase/time-alignment must be good, or it's just not worth implementing.
> >
> > 1. bandpass filter from 4k/8k/16k to say 100k ?
> > 2. active HPF with make-up gain (i'm not sure how to do this)  ?
>
>First make a highpass filter for the above frequencies (switchable resistors
>for frequency). A simple Sallen & Key filter will probably do the job well
>enought. Select a Bessel-Thomson or Gaussian responce.
>
>Then, just like in an equalizer, put the output of the highpassfilter to the
>wiper of a pot and then the ends to a positive and negative mixing bus. 
>Add the
>original signal to the positive mixing bus through a resistor. You are looking
>at 4 op-amps including an input-buffer (which is highly recommended unless you
>have a good low-impedance source).
>
> > does anyone have experience with inductors?  what are they like in real 
> life?
>
>Reactive? ;O)
>
>Cheers,
>Magnus