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:

• 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.
• 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.

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:

My final project used this wiring diagram (simplified for anyone to understand properly):

Icom IC-705 TX SSB parametric EQ setup