[sdiy] Noob Question: Passive Filter Design

[Nils Pipenbrinck]

Cary Roberts wrote:
> My favorite EQs are all inductor based. Most EQs on the market today
> do not
> use inductors but use gyrators to simulate inductors.
>   
Sorry for the guitar-amp related rant, but:

The 5 band equalizer of some well known Mesa Boogie amplifiers is also
inductor based.

I have rebuilt the circuit of the mesa-triaxis using gyrators. I have
the amplifier at home, so I was able to measure the series resistance
and model the gyrators after it. Result: The frequency response is close
to the real unit, but it lacks the sweetness of the real thing.

Later I rebuild the circuit using self wound inductors. Lots of fun: My
fiancé had to to hold the wire spindle while I was counting and winding
the inductors. Payback time for all the days where I have to hold yarn
for her knitting...

Anyway, the sound became better. It was less sterile than the gyrator
but it was still not the same. My unscientific conclusion was that you
not only need to have identical inductors but that the placement of the
inductors relative to each other also is part of the sound. It seems to
me that in this filter the inductors go slightly into saturation and
influence each other in strange ways.

This is when I stopped cloning a sound that I already have.. My initial
intention was to publish a schematic of a mesa filter work-alike for the
stomp-box community but I failed because I never came close enough to
the real thing. And rolling your own filters is neither fun nor cheap.


Inductor magic!

  Nils





>
> -Cary
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
>