The Mighty Koss SB40 & DIY YAESU Microphone Adapter with PTT socket and DIY PTT foot switch

The Mighty Koss SB40 Headset with dynamic mic

Yaesu radios expect a dynamic microphone input.  Condenser microphones require power to operate (often called phantom power).   I have been using the Koss SB40 for about 2 years now. First with my Yaesu FT-891 and exclusively for the last 5 months with a Yaesu FTdx10.  The sound and build quality is amazing and the price is spectacular.  I often use it on the 3905CCN QSL nets for hours at a time, switching from band net to band net, and I always get great audio reports and comments on my audio quality. It is comfortable and remains comfortable. Finally, at a cost of $30 new, it is a no-brainer!! 

To connect the Koss headset for Yaesu operations requires a microphone adapter cable.

DIY Microphone adapter cable (blue) for the Yaesu FTdx10(top radio).   The adapter cable plugs into the FTdx10 via RJ45 8-pin plug and brings out the microphone audio to a 3.5mm female mono audio socket and out to a 1/4" female mono audio socket for PTT via a foot switch.

Many radios now sold by Yaesu use an 8-pin RJ45 plug-in module.  Below is microphone wiring schematic for the FTdx10.  While different Yaesu mics and rigs may have different features, wires number 4 - 7 are standard for Yaesu mic audio and PTT operations.  Microphone adapter cables can be readily purchased, such as the INRAD M-YM adapter which lists for $14.95.   While I purchased an INRAD adapter, I needed another microphone adapter and easily made for one only a few dollars.   

Yaesu 8-pin RJ-45 wiring

CAT-5e RJ-45 cable connector. Pin wiring order
is #1 from bottom to #8 top (blk wire).  In the plug
above, wire #4 MIC GND corresponds to the blue
wire, #5 MIC is the white/blue wire above the blue,
wire #6 PPT is the green wire, and #7 GND is the
white/black wire.   

Below is an image of an adapter cable being fabricated for an old  CAT-5e cable, a 3.5mm female mono audio extension cable ($3) and a 1/4" female mono audio socket ($0.50).  The wiring schematic above shows the 8-pin wiring as viewed looking at the Yaesu RJ45 socket.  When viewing the plug of the CAT-5e cable, wire ordering goes from #1 and bottom increasing to wire #8 at the top.  The above RJ-45 plug is of the CAT-5e cable.  Wire to pin ordering was verified using a DVM testing continuity from the RJ-45 pin to the individual color coded exposed wires from (cable with end cut off).  Pin wiring order is #1 (white/orange) from bottom to #8 at the top (black wire).  In the plug above, wire #4 MIC GND corresponded to the blue wire, #5 MIC was a white/blue wire above the blue, wire #6 PPT was the green wire, and #7 GND was a white/black wire.   

The microphone adapter cable plugs into the Yaesu via RJ-45 8-pin plug and brings out the microphone audio to a 3.5mm female mono audio socket (CAT-5e wires #4 & #5) and out to a 1/4" female mono audio socket (CAT-5e wires #6 & #7) for PTT via a foot switch.  In addition to the FTdx10, the adapter cable has been used on an FT-891. 

PPT foot switches can be purchased for about $50 or more.   A DIY PPT foot switch was made using a  6ft 1/4” to 1/4” Audio Cable ($6 eBay) and momentary foot switch ($3 AliExpress).  See image below.   The exact same foot switch is sold by Adafruit product ID 423 ( & DigiKey 1528-1137-ND) for $7.50 plus shipping.  One could get a switch much quicker, paying the few dollars more, from Adafruit/Digikey, as apposed to AliExpress’ 2 month slow boat from China shipping.

Fabrication of a Yaesu microphone
adapter cable.

DIY Yaesu microphone adapter cable
with PPT socket.

PPT foot switch made from a 1/4" audio cable
and a momentary switch.

FT-891 Tip:  Use 1ft CAT6 patch cable and F/F RJ-45 coupler which can be cheaply purchased from from a vendor like Monoprice.com.  Remove the FT-891 control head, unplug the Yaesu microphone, plug the patch cable & F/F coupler, and then replace the control head.   Now you  have access to RJ-45 connection without needing to remove the control head.   This allows for switching between the regular hand mic and the a headset.   

For those too timid or just don't have the time to build the Yaesu audio adapter, the INRAD M-YM audio adapter can be purchased at most main stream vendors; list price $14.95.  See the INRAD M-YM audio adapter image below.

The INRAD M-YM audio adapter.