[Icom] D-104 Silver Eagle microphone

[Bill Gode, Sr.]

The Silver Eagle has a high impedance crystal cartridge, but it also has 
a transistor preamp in the base for driving a wide range of radios and 
load impedances.  The stock mic will work with your Icom (use that DC 
blocking capacitor), but you can improve things with a little time and a 
soldering iron.

If you rewire the microphone so the preamp is powered by the DC present 
on the mic jack, you can dispense with the 9 volt battery.  You can 
further rewire it to keep the preamp "on" all the time to permit VOX 
operation with PTT override.

If you add a 500k or 1 megohm resistor in series with the crystal 
element at the preamp's input, you can realize better low end 
performance, if desired.  Finally, a small resistive pad to further 
attenuate the preamplifier's output is advisable, along with a 1 uF DC 
blocking capacitor.  Play with the rig's transmit bandwidth and tone 
controls to fine tune the mic to your voice and personal preferences.

The stock preamp is quite resistant to RFI and a modified D-104 can 
sound considerably more extended in both highs and lows than a Heil HC-5 
cartridge.  It will also have enough output to preclude cranking up the 
mic gain and compression controls.  If you want Heil sound, get a Heil 
mic and don't destroy that Silver Eagle - the current new price is $200 
from most dealers!

73,

Bill, W9NHQ

Adam Farson wrote:
> Hi Dave,
> 
> If the D-104 is fitted with a high-impedance crystal or ceramic element, it
> will not match the low-impedance Icom mic input correctly. I would recommend
> that you install a Heil HC-5 element in the D-104 head (Heil may even offer
> a mounting kit). This will ensure the correct impedance match and drive
> level. You will need to connect an 0.47 ?F capacitor in series with the
> element and the mic input lead, to block the radio's electret polarising
> voltage from the element.
> 
> If the D-104 already has a low-impedance (500 or 600 ohm) dynamic element,
> it should work. You will need the same series capacitor as described above.
> It may be necessary to turn up the MIC GAIN and COMP controls for adequate
> drive.
> 
> The mic connector pinout is shown in the user manual for each radio.
> 
> Best 73,
> Adam, VA7OJ/AB4OJ