[TenTec] 566 v3.029 and 707 Regal mic
jruing at ameritech.net
Fri Nov 30 16:18:57 EST 2012
On 11/29/2012 12:46 PM, Rsoifer at aol.com wrote:
> FYI, the output impedance of the 709A is
600 ohms, while that of the 707 is > 50k ohms.
The O2 specs call for >10k.
Hmmm... Not sure, but...
I don't think these impedance variations are material - at least not
enough to cause problems or to really explain what we are seeing in
differences in performance in this case. Generally, modern audio gear
does not seem to care about impedance. RF does, but audio gear not so
Others, with serious degrees like Jim B K9YC, can better explain why,
but I have read, and have long believed, that wide variations in
impedance in this case is not material, except in certain cases, such as
when you want to drive a PA with a high impedance microphone, or a
guitar amp with a high impedance pickup, and you wanna use a 100 foot
cable in between. (Then you might want a DI box or other
especially the bit on microphone impedance, and how the audio chain
differs from an RF chain.
Or try this:
"Most audio inputs are 'bridging' inputs, where
the load impedance is much higher than the
signal source impedance. In that way, when
the signal is fed to an extra piece of kit in
parallel the signal level does not fall appreciably.
Thus at line level, most modern outputs are
< 100ohm impedance and inputs are
usually > 10kohm.
When Should Source and Load Impedance Be Equal?
When a cable length is more than about a tenth
of the wavelength of the highest frequency
present, then the frequency response may
become uneven. For audio, the highest frequency
is about 22kHz for CD, making the wavelength
a little over 8km assuming a cable velocity factor
of 0.6. 800m is much longer than most audio
cables in practice, so this is not usually a worry."
Or what it says here:
particularly re: mic input matching.
-- Thus, I am thinking variation in microphone impedance may not be
material, and at least not the reason we are seeing differences in the
case at bar.
Just MY take...
At least my intentions are good... and my road to He** is very well
paved with my good intentions ! ;-)
----------------- K8JHR ----------------------------
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