[sdiy] L, C, and sometimes R

[Theo]

One other easy way (without complex math) to look at (quite a number of)
filters is as frequency depended voltage dividers.
This makes also clear why the load on a RC or LC combination needs to be
taken in account.
And what the difference in effect of load on a RC LP stage or a CR HP stage
is.
You can even calculate frequency responses of filters with multiple stages
this way.

When in 2nd grade high school "designed" my first filters like this, a bit
guesswork and even more trial and error, but it kind of works.

Cheers,
Theo




----- Original Message -----
From: jhno <ear at heldscala.com>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Saturday, September 11, 2004 11:19 AM
Subject: [sdiy] L, C, and sometimes R


> i really like how this page explains the basics of inductors and
capacitors:
>
>
http://www.nzart.org.nz/nzart/examinat/amateur%20radio%20study%20guide/Cours
e%20Files/Caps%20Inductors%20Resonance/STUDY%20NOTES%20-%20CAPACITORS%20INDU
CTORS%20&%20RESONANCE.htm
>
> much clearer (to me) than everything else i have read.
>
> interestingly, it talks about e.g. capacitive and inductive reactances
> combining to make a notch filter, by causing very little current to flow
at
> the resonant frequency.
>
> hmmm. i usually think of it like this:
>
>
> - capacitors (C) pass high frequencies; inductors (L) pass low
frequencies.
> therefore, a series C is an HPF, and a series L is an LPF.
>
> - in parallel connection, those frequencies are shunted to ground instead
> of passed on. hence a parallel C is an LPF, and a parallel L is an HPF.
>
>
> so how incomplete or inaccurate is this over-simplified model? in what
> practical aspect does it fail, when designing/analyzing high-quality audio
> circuits?
>
>
> i think the main problem is that i tend to think of circuits operating as
a
> state machine of voltages. it seems like if you know all R and V in a
> circuit, you have all the information - since I can be derived from them.
> hence I seems like extraneous information and really just a different way
> of looking at the system. it is useful to use this point of view when
> calculating the behaviour of a transistor or tube, but couldn't all that
> information technically be represented, albeit awkwardly, in terms of R
and
> V?
>
> in any case, my lack of intuition for I and V mean that i do not easily
> understand e.g. the effects of the opposite phase shifts imposed by L and
> C, and the relationship or combination of capacitive and inductive
> reactance.
>
> please reveal the crucial point that makes it all fall into place - !
>
> jhno
>
>
>
>
>