On Fri, 2007-11-16 at 07:25 -0600, Bob McGraw - K4TAX wrote:
> The D-104 has proven to be a time tried consistent performer.
> Unfortunately, many D-104 mike today have an element that is defective.
> Defective not as in no or low output, but brittle thus one that sounds bad.
> New replacements are hard to come by and somewhat expensive. Replacements
> such as the Heil HC-5 work and typically sound good. However, to drive
> older radios, the amplified base stand is usually required. But this then
> is no longer a D-104.
The D-104 is a crappy microphone for SSB, always has been. It has a
rising characteristic intended (in the 30s) to emphasize the highs at
the transmitter that were rolled off in the typical AM receiver IF
selectivity that had a very rounded pass band. Further the crystal and
ceramic D-104 were designed to work with a very high impedance load for
solid state, preferred load a megohm. Today a high impedance solid state
audio input impedances is likely to be under 100K. That load on a D-104
changes it from rising to peaked and falling, makes it sound muffled. It
it still had the rising characteristic with the solid state input Z, it
can overdrive audio and balanced modulator with audio components
rejected by the SSB filter unless in super wide SSB mode which draws a
lot of fire on the bands.
>
> Secondly, those with the amplified base stand may have their problems too.
> Many due to efforts to configure them to drive different loads and various
> PTT switching arrangements.
Or simply from supply VOLTs of audio to an input circuit designed for a
couple millivolts. NO ham rig has ever needed an amplified microphone.
Amplified microphones were only needed with fixed transmit audio gain
CBs that were intentionally very under modulated to absolutely prevent
over modulation.
>
> At the same time, in view of all of the above, a good D-104 is an
> outstanding performer on SSB and AM too. The following link is very helpful
> in wiring the mike, configuring the PTT switching and such.
> http://www.shadowstorm.com/cb/Astatic_D-104_Papers.html
>
> 73
> Bob, K4TAX
>
Yes, I have a D-104 (case) hooked to my Corsair II. The cartridge is a
Shure limited bandwidth communications element no longer made.
73, Jerry, K0CQ
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