With the popularity of gaming and Skype, some nice headphones with microphone booms are available quite cheaply. I bought one of these: "Gearhead" AU3700S Computer headsets for £10.91. This one has 3.5mm stereo jack plugs for the microphone and headphones. I noticed that quite a lot of the headsets now come with a USB plug, which presumably has a USB soundcard built in. Not much use if you want to connect to an old analogue wireless set! Make sure you get one with jacks.
To use the headset with a radio we need some kind of adaptor box. This will have socket(s) for the headset and leads to plug into the microphone and headphone sockets on the radio. It will have a Transmit/Receive switch or PTT button, and with supply a bias Voltage to drive the electret condensor element in the microphone.
So this is what I built. I decided to stick with the "Y" adaptor on the headset, because it means that the box becomes more versatile having separate sockets for mic and headphones. I wanted the box to be well screened because there maybe high RF fields around, so I used a diecast aluminium box, from Hammond Manufacturing (Pt. No. 27969PSLA) - it is one I picked up last year at a Radio Rally. I found some flexible 9-way screened cable - more conductors than needed but I doubled up the ground connections to try and keep the impedances low.
But we have to be careful not to introduce ground loops. There is the cable screen, there is the microphone ground, there is the headphone ground and there is the PTT ground, and really they should all be kept separate. Trouble is a lot of jack sockets have a metal fixing nut that connects the barrel of the jack to the metal box that they are mounted on.
Here is a circuit - drawn on CAD as you can see :-)
The "spare" pins on the mic connector are used for "up" and "down" buttons on the microphone - but I haven't used them here.
The headphone circuit is kept completely separate - partly because the radio offers the facility to listen to your own SSB transmissions, so we don't want any audio getting back into the microphone socket. I used RG58 for the interconnecting cable, as we only need a mono signal for the 'phones.
the TX/RX switch is just a bog-standard DPDT toggle switch.
So here are a couple of pictures of the "innerds".
The finished box looks like this:
So there you have it, a Bank-holiday-Monday headset to FT847 adaptor box.
Further notes:The 3.5mm Jack is an EST Part: Part no. MJ073H, from Ebay, here http://www.ebay.co.uk/itm/351607508978
8 pin microphone connector also from Ebay: http://www.ebay.co.uk/itm/111965139338
But found the thread on the locking ring was poorly made, and won't screw up on the socket - so I will have to change it ... a pigging nuisance!