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From: Bob Eldred on 10 May 2005 10:39

"Tom MacIntyre" <tom__macintyre(a)hotmail.com> wrote in message
news:usnv71phba7ale1j8u0lit3gefkp90gs2g(a)4ax.com...
> On Mon, 9 May 2005 14:43:33 -0700, "Bob Eldred"
> <nsmontassoc(a)yahoo.com> wrote:
>
> >
> >"Music Man" <j.michael(a)cwcom.net> wrote in message
> >news:427b97b1$0$335$cc9e4d1f(a)news.dial.pipex.com...
> >> How does impedance mismatches alter signals?
> >> I know you lose HF but always wanted to know how different frequencies
> >> are affected by different circuitry.
> >>
> >> Thanks
> >
> >First off, maximum power is transferred when impedances match.
>
> I may be wrong, but, in strictly technical terms, isn't it when the
> resistive components are equal and the reactive components are equal
> but opposite, complex conjugates (?) of one another?
>
> Tom

Yes, you are correct but I'm trying to keep it simple and not bring
reactance into it at this level. First things first is a basic understanding
of the underlying principles and why line reflections occur and are
important. If the basic concepts are not there, complex conjugates are
going to fall on deaf ears.
Bob


From: Music Man on 15 May 2005 13:06
So are you saying,basically,that the high capacitance can't deal with the
faster frequencies?
Thanks


"John Popelish" <jpopelish(a)rica.net> wrote in message
news:T96dnRWnHqZAPebfRVn-vg(a)adelphia.com...
> Music Man wrote:
> > How does impedance mismatches alter signals?
> > I know you lose HF but always wanted to know how different frequencies
> > are affected by different circuitry.
>
> Impedance is an expansion of the concept of resistance to include
> time. Resistance relates voltage across something to the current
> through it. Another way to say ohms is volts per ampere. But that
> description of the relationship between voltage and current does not
> involve time. It describes stuff that only consumes energy when
> voltage is connected across it, and does so, regardless of how long
> the voltage is applied, or how fast it changes.
>
> When you include the possibility of energy storage as well as
> consumption, time becomes an important factor. For example,
> capacitance stores energy in proportion to the square of the voltage
> across it (E=(1/2)*(V^2)*C), but it takes time for a given current to
> build up that voltage (I=C*(dv/dt) or the capacitive current is
> proportional to the time rate of change of voltage across the
> capacitor). So once energy storage is involved, you need a two
> dimensional description of the relationship between voltage and current.
>
> Back to the frequency effects: If an impedance has a capacitive
> component, then the current that passes through it will increase when
> the voltage changes faster. If the current through that impedance
> arrives through a series resistance, then as frequency rises, more of
> the total applied voltage will get used up across the resistance
> (because the current is rising) and less will appear across the
> capacitive impedance (because the total of the resistive and
> capacitive voltages must add up to the applied voltage). This forms a
> basic low pass filter if the signal across the capacitor is the output.


From: John Popelish on 15 May 2005 13:37
Music Man wrote:
> So are you saying,basically,that the high capacitance can't deal with the
> faster frequencies?
> Thanks

Capacitance deals with high frequencies just fine, by sucking current
out of it. ;-)

Seriously, the effect is that the higher the frequency, the lower the
impedance (volts per ampere) the capacitor exhibits. This can be a
bad thing if you are trying to avoid it (like sending audio through a
long chunk of high capacitance cable from a high impedance source like
a guitar pickup, and the cable soaks up the higher frequencies) or
real handy if you are making use of the effect (like you do in a tone
control circuit).
From: Music Man on 16 May 2005 19:59
So what is the relation to frequency and capacitance John?
Could you explain on how audio signals are "expressed" in electronic
circuits.
What is need to creat a clean signals?How resistors creat noise and add to
signal?
What I mean is why would a Neve mixing console sound better than a cheapo
desk.

Thanks


"John Popelish" <jpopelish(a)rica.net> wrote in message
news:eNGdnRDtbp46GBrfRVn-jg(a)adelphia.com...
> Music Man wrote:
> > So are you saying,basically,that the high capacitance can't deal with
the
> > faster frequencies?
> > Thanks
>
> Capacitance deals with high frequencies just fine, by sucking current
> out of it. ;-)
>
> Seriously, the effect is that the higher the frequency, the lower the
> impedance (volts per ampere) the capacitor exhibits. This can be a
> bad thing if you are trying to avoid it (like sending audio through a
> long chunk of high capacitance cable from a high impedance source like
> a guitar pickup, and the cable soaks up the higher frequencies) or
> real handy if you are making use of the effect (like you do in a tone
> control circuit).


From: Buddy Smith on 16 May 2005 21:30
Music Man <j.michael(a)cwcom.net> wrote:
> Could you explain on how audio signals are "expressed" in electronic
> circuits.

If you want to learn more about audio equipment, I'd start with the
prosoundweb's study hall. Impedance:
http://www.prosoundweb.com/include/php/sitejump.php?lid=www.whirlwindusa.com/tech03.html

ttyl,

--buddy
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