On Tue, 2006-03-21 at 19:44 +0000, Rob Atkinson, K5UJ wrote:
<<<mike input is high impedance (about 10K) unbalanced -- which is the
> usual amateur practice (strangely).>>>
>
> this is amazing. It is absolutely not the industry standard now. with the
> apparent exception of ten tec, hi Z input rigs have not been made in years.
> it sure goes to show you how important it is to ask the mfr. I would have
> never guessed TT was still using hi Z. No wonder all these guys who buy ten
> tec rigs have problems. they have their low Z gear/mics on hand and their
> audio sounds bad on the TT rigs. As i mentioned last week, this is more
> evidence of a company that has all cw ops on the payroll, hi.
>
> rob / k5uj
>
>
10K is NOT HIGH impedance. Its moderate impedance at the best. 1 MEG is HIGH
impedance.
Some vintage Kenwoods take 50K as "high" impedance.
So long as the NOISE of the audio stages and the gain of those stages is
adequate, a 10K
load on a 600 ohm microphone works fine. There should be absolutely NO
distortion, just
low level if the gain isn't high enough. No odd frequency response, just the
possibility
of some circuit noise from the extra gain required.
Its sure that the dynamic microphones and electret microphones are mostly going
to be on
the order of 600 ohms unless the dynamic microphone (like my EV 664) has a
transformer
for high impedance. In that case 10K is LOW for that high impedance connection
and
should cause some odd frequency response at best. No crystal microphones (like
the
vintage D-104) will run happily with a 10K load, they prefer at least half a
MEG or
higher. And then the D-104 has a poor response for SSB, rising with frequency
with a
peak outside the passband of the transmit filter (except for those running a 6
kHz SSB
filter).
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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