[sdiy] hi shelving filter

[Byron G. Jacquot]

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

The reason we rap inductors is that good ones are hard to find.  You need
fairly large ones to be really useful in the audio bands: 10's of mH up to
maybe 2H.  The common ones are down in the uH range.  Most of them are
unsheilded, and will do exactly what Harry says.  The DC resistance of a lot
of the cheap inductors is also so high that their bandwidth becomes
approximately the entire audio spectrum.

If you're curious about EQ designs, you might cheak out the white paper
offered here: http://www.forsselltech.com/white_papers.htm

I've been playing with the gyrator design, and I'm quite pleased with it's
preformance...and especially the independence of Q, frequency and cut/boost
depth.  Keep the Q of the bandpass sections low enough, and the phase shift
isn't too objectionable.

Byron Jacquot