>> The ME66/K6 outputs a low impedance
>> signal designed for 600 ohm systems.
> The output impedance of the K6 module is 200 ohms and the minimal
> terminating impedance of the recorder is 1000 ohms.
> This impedance matching rule however does not apply any longer to
> modern microphones and audio recorders that have their own power
> supply
> and come with sensitive electronic preamplifiers.
Raimund,
Agreed, the spec of modern equipment is much higher than the old stuff
but what I said was "600 ohm *systems*" The exact impedaznce match
doesn't matter and 1000 ohms works fine. My MKH mics have a very low
output impedance, I think under 20 ohms, but they are optimised to
work into 600 ohms systems as in the spec. They are likely to run into
current overload if you try to match their impedance into 20 ohms.
As you said, Impedance matching to get optimum transfer energy is not
applicable in any system with amplification as it was with carbon mic
telephones. BTW the 600 ohms spec comes from open wire telephone
lines. Anyone still remember them and how they used to cross over
every few poles like cat 5 twisted pair cable?
Ideally for a flat frequency response there should be no mismatch
echoes at either end. This is really only applicable to video signals
where the output impedance around 75 ohms should be matched by 75 ohm
cable and terminated by 75 ohms. However if you try to feed a 20,000
High-Z mic into as long 100 ohm cable you will lose high frequencies.
This can be expressed as a current echo at the far unterminated end
and if you terminate it with 100 ohms you will get a flat frequency
response but will lose 46 dBs.
This of course is theoretical claptrap. :-)
In practice mic cables have various impedances but in practice you can
simply ignore this in 600 ohm systems. Any frequency response
difference will be under 1 dB and therefore inaudible. My practical
advice is that if a bit of conductive string works, use it. :-)
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
|