KOSS SB45 audio setup to IC-705

Icom IC-705 alows distinct setups for RX and TX on SSB, FM and other modes. When you connect a new headset with microphone, like in my case the KOSS SB-45, it’s interesting to adjust the audio setup. Here are my details.

Physical connection

Icom IC-705 uses one 3.5mm TRS jack connector for the audio exit and one 2.5mm TRRS jack connector for the microphone input plus functions. I wanted to leverage this two connection jacks so I decided to create my own junction box. I prepared mine with two female 3.5 jacks for the KOSS SB-45 headset male connectors, one DIN connector with 6 pins and an RCA connector for the PTT/footswitch.

Why this was necesary?

It was necessary because many reasons:

If I wanted to use PTT while using a headset I was unable due to main connector was already used and SEND/ALC was not seen as an option.

Icom provides 3.3V or 8V (option selectable via rig menu) the 2.5mm TRRS jack connector but unfortunately the KOSS SB-45 provides 3.5mm TRS jack with tip and ring interconnected for increased computer sound card support, which is a problem from ham radio.

Headsets use an electret captuse and it requires 3.3V to operate but providing voltage from radio can be risky if now well isolated both parts.

Headset mods

In general all the electret headsets require similar adaptations to radio transceivers. While searching information for the KOSS SB-45 I came across a japanese colleague article on FBNews, an adaptation for computer headsets documented by Florian, DF2ET, and the adaptation cable created by Alex, KR1ST, that showed the exact same issue I was having, in his/her case using a different headset. I reviewed the article and decided to build my junction box based no the concepts learnt from this colleague. A visual excerpt of all of those projects follows:

Icom IC-705 TX SSB parametric EQ setup