[sdiy] Noob Question: Passive Filter Design

[Harry Bissell]

Most of the advantages and disadvantages of inductors vs caps
come down to parasitic elements. These are aspects of the component
that are undesirable if unavoidable.

A perfect capacitor is just that. A ~real~ capacitor has things like
series resistance (zero is ideal), dielectric absorption and other
losses, stray inductance, etc.

An inductor has series resistance, stray capacitance, magnetic losses,
and the ability to pick up external magnetic fields and convert them to 
signals, as well as send out magnetic fields and interfere with other
sensitive components. They also have "Q" or quality factor, a representation
of their ideal characteristics to their non-ideal ones. "Q" is vitally
important in filters, usually high-Q is desirable.

So in short (this could be a textbook...

Capacitors are usually the first choice for filters. The parasitic elements
are not so difficult to deal with as those of inductors. At audio frequencies
most if not all of the capacitor's parasitics are negligable.

Inductors are added when you want to get higher attenuations than simple
R-C filters give, or when you need resonance in a passive filter (bandpass
anyone ?)

Sorry I don't know of a good text...

H^) harry


----- Original Message -----
From: Sam Ecoff <secoff at execpc.com>
To: sdiy DIY <synth-diy at dropmix.xs4all.nl>
Sent: Mon, 03 May 2010 23:46:22 -0400 (EDT)
Subject: [sdiy] Noob Question: Passive Filter Design

Hi All,

So, I'm still slogging slowly through an EE degree, and we've gotten  
up to the point where we're discussing passive filter design, and  
we've learned how to construct passive highpass, lowpass, bandpass,  
and band reject filters using various combinations of resistors, caps,  
and inductors. Have seen a fair number of filters, I asked my  
professor what the advantages/disadvantages of using caps vs.  
inductors are, especially as the discussion relates to audio circuits,  
but he was unable to answer that. Can anybody help me out? It would be  
especially helpful if anybody has a suggestion for further reading.

Thanks!

Sam E.
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-- 
Harry Bissell & Nora Abdullah 4eva