Build an 8 pin mic adapter for your IC-705

An IC-705 8 pin mic adapter can be built for under $15. The Icom IC-705 is an amazing radio. It’s perfect for everything from DC to daylight. The microphone that’s supplied with the radio – the MH-243 works, but what if you need or want to use a different microphone? A recent search on the internet found many aftermarket adapters and converters, but one result had a circuit diagram. So rather than spend $40 USD and wait weeks for delivery it was time for a trip to the local Jaycar to grab some bits to make my own.

I use my IC-705 as an IF radio for microwave and could really use a ‘K’ generator to signal the end of transmission for weak signal 10 GHz QSOs. The 8 pin option was the best suited to solve this problem.

There is a caveat on this circuit… It works perfectly when the power to the radio is an external source. When the radio is running on its internal battery, the audio wasn’t as good and there was unidentifiable background noise. My test was with two microphones, the SM-30 desk mic and an HM-219 handheld mic. This generic mic is supplied with many Icom transceivers these days such as the IC-9700 and IC-7300.

Parts List

If you’re keen to build this, then you’ll need…

• 1 x 8 pin male inline mic connector – Altronics
• 1 x 4 pole 2.5mm male connector – Jaycar
• 1 x 33k resistor
• 1 x 1k resistor
• 1 x 1 uF monolithic capacitor
• a short length of 2 core + ground cable

When using an Icom desktop microphone such as the SM-30, it’s necessary to switch MIC terminal 8V output to ON. Go to the IC-705 set menu, push MENU -> SET -> Connectors -> MIC Jack 8V output to ON.

Note:

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