[sdiy] hi shelving filter

[harrybissell]

LOL... inductors in high gain circuits (or low level circuits) are REALLY good
at picking up stray magnetic fields as well...

hmmmmmm  what do you think ???   :^P

H^) harry

mark s wrote:

> 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