[sdiy] hi shelving filter

[fmg]

mark s wrote:

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

Mmmnn...no, I use them often. Actually that's the component power
cables find first when enter in most of my cards. Chokes apart,
they are useful in other applications, but the word "inductor", like
the word "thing" doesn't explain too much, there are microscopic ones
and others that weigh tons, also, for a same type there is a variety
of uses. There are "inductors" that doesn't have the look but act like
such (transformers are magnetic coupled inductors, your DVM leads are
inductors, long pcb traces are small inductors... and... people can use
compasses mainly because this rotating world is a BIG inductor).

More on topic, as Harry said, they are prone to capture "noises" and this
is notoriuos specially when are in small signal path. But this is true only
in part, (otherwise RF preamps, TV, cell-phones, etc would never have existed[*])
the "capacity to catch" EMI depends on where and how they are mounted in PCB,
also the body size plays a role too. A tiny 500uH resistor-like is less prone
to capt noises than a 500uH one made of 40 turn of wire in a glass of water, in
fact, a little experiment can be done with one of these inductor connected to
the mic input of a pream through a long unbalanced cable, and walking through
the house trying to "catch" something. Most of the "noise" will come from the
small-inductance-large-body cable, and a very small amount (or none) from the
large-inductance-small-body inductor. Seriously, try it!

RF people usually tell marvelous stories about inductors that could make you
cry under wonderful emotions, don't trust them, they are just exaggerating. In
the other end there are audio people that can tell you stories of MIR intercom
captures, self-oscillations or strange diseases, all related to inductors. I
recommend you not to trust them, all those are pure fantasies.
Unless you live below a 300KV transformer, you don't have to worry about inductors.

This could sound strange for someone, but I'm using inductors more often than
before. With so many RFI and those digital equipment sorrounding everywhere I
atually can't conceive an audio gear without them.

OTOH, compared to capacitors, resistors or semiconductors, inductors are
the best "user-friendly" component to diy.


Fabio Gonzalez

[*] re-thinking, not having them doesn't sound too bad


harrybissell wrote:
> 
> 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
>