While I enjoy operating the IC-705 with the HM-243 microphone that comes with the IC-705, I wanted to try operating with other microphones, because when operating on the DV mode, I was worried about the difference in sound of handheld transceivers such as the ID-31 or ID-51. Also, in order to use a desktop microphone when operating for a long period of time at home, I conducted an experiment to find out whether a home-made conversion cable can be used instead of the HM-243.

Microphone Jack of the IC-705

4-pin plug is used for the IC-705 microphone jack, as shown below.

The IC-705 Microphone Jack Pin Assignment

★Apply 3.3 VDC through a 470Ω in series or directly apply 8 VDC (maximum 10mA)

The HM-234 plug has 4 pins. However, the regular 3-pin plug can also be used with a speaker microphone that has no key output function. I confirmed that the similar speaker microphone that is used with the ID-51 and ID-31 can also be used with the IC-705.

An HM-186LS speaker-microphone for handheld transceivers is connected to the IC-705.

Transmitting with the HM-186LS. The audio can also be heard from the HM-186LS.

MIC conversion cable for the IC-705
◎ Components needed
・8-Pin metal microphone jack for desktop microphone.
・Φ2.5mm 4-pole plug
・Cable (2-wire or 3-wire shield)
・Resistor (1kΩ×1、3.3KΩ×1)
・Capacitor (1µF×1)

◎ Wiring

Moreover, when connecting a microphone other than the standard HM-243, UP/DN keys on the connected MIC cannot be used.

I purchased the necessary parts at a shop in Osaka’s Nipponbashi electric town, then made this conversion cable.

The completed conversion cable

To use an Icom desktop microphone, it is necessary to switch「MIC terminal 8V output」 to 「ON」in the IC-705 Set menu.

For firmware version 1.2 Push [MENU], then touch [SET] ＞ [Connectors ]＞ [MIC Jack 8V output]→「ON」.

Connecting the completed home-made conversion cable to the SM-30 and trying on transmitting.

There are various microphones can be used with the IC-705 these days. Since my experiment of connecting my home-made conversion cable with the desktop microphone, I realized that there are many types of microphone can also be connecting with the IC-705 and works effectively, it will be interesting to check the sound quality changes by using a variety of microphones with the IC-705.