Icom IC-7300 Microphone Input Arrangement
In common with with their other rigs Icom have very kindly applied some DC to the microphone input pin (No 1) on the front panel microphone socket so that an electret condenser microphone can be used without any concerns about how to supply it ( Drain of the FET within the microphone capsule).
Here is the circuit of the microphone input arrangement within the IC-7300, it can be seen that the 1K resistor effectively becomes the drain load for the FET in the microphone capsule and the DC supply is very well de-coupled at DC, AF and RF thanks to the capacitors C1017,1018 and 1019. Any two connection electret insert can be connected directly to the microphone input (Pin No 1) and ground (Pin No 7) and the overall frequency response adjusted in the TX TONE menu to suit your own voice characteristics.
To enter the transmit mode you can either use the TRANSMIT button on the front of the rig or use a foot switch which is what I use and find very convenient. I use a foot switch which is intended to be used with a tattoo outfit and these are available on e bay for under £5 and they are of sturdy construction. I have made up a connecting lead which has an 8 pin plug on one end for the mic input of the rig and a free 3.5mm socket for the microphone input and a free 1/4" socket for the foot switch.
You can now try out lots of different electret microphones or boom headset combinations to find out which suits your voice best and bore everyone on the band with your numerous audio tests HI ............................
Just as a matter of interest......................
Don't believe the utter nonsense put around by an American manufacturer of very expensive microphones and inserts that if you connect a dynamic microphone to the mic input (Pin No 1) of an IC-7300 the result will be in their words "Smoke City" because it is obvious that if you look at the rig's input circuit below that even if you connect a short circuit to the mic input the maximum current drawn will be only about 7mA, totally insignificant and will not harm the rig in any way. A coupling capacitor should however be used, the value of which should be between 0.47 and 10mfd, lower values of capacitor will reduce the LF frequency response.
Microphone Input Circuit within the IC-7300
Microphone Adaptor Lead
