Hello, I picked up a sennheiser mic at a flea market in very good condition. It has a standard 3 pin xlr connection. Is there a way to wire this to an Icom 718,746 with or without some type of interface? Any help would be appreciated. Thanks, Mike w2waw
Plug-n-Play cables for the 3 pin XLR connector microphones are available from Heil Sound.
The DIY information is also on that Heil web site.
You need to handle the radio Push To Talk (PTT) function via a footswitch or hand switch -- UNLESS you are using VOX. Heil has that solution as part of there cable sets.
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Greg, Thank you very much. Mike w2waw
I like Sennheiser microphones, since it has a XLR connector I think we assume it is a dynamic type microphone. The bad news is ICOM's use an electret microphone element which has a J-FET amplifier in it and requires a DC voltage to run it.
Originally Posted by W2WAW
There is a solution but you will need a preamp circuit. I am attaching a circuit that works very well and is made for a ICOM IC-718. The circuit uses a J-FET OP-Amp and if you choose to use it, follow the schematic as ICOM's are very sensitive as to how their "grounds" are hooked up.
That's a nice looking schematic! The older Icom preamps used discrete components, and it is good to see an IC circuit that will work with the phantom power that is supplied by the radio.
Icom has incorporated the phantom powered mics for many years. The advantage is that the radios are almost immune to RF feedback problems when running soundcard audio for digital programs. The disadvantage ( which is really quite small ) is that you DO have to use an interface such as the one above, if using anything but a mic specifically designed for the radio.
I once built a two transistor audio interface for a Heathkit phone-patch that I used with a 720a. I still have the phonepatch with the interface built in, AND the radio that I used it with.
Don't do any phone patches anymore, though. Satellite phones and the internet have pretty much eliminated that form of operating.
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Thank you for the info, I appreciate your time. Mike w2waw
Thank for the comments. I should really put some pin numbers on the IC-718 side of the hook-up but the name terminology is the same. ICOM on their microphone connector provides a regulated +8 volts with an advertised limit of 10 mA along with the microphones normal phantom power. Current isn't a problem since the OP-Amp only draws 2 mA. Actually, the output of the OP-Amp (biased at 4 V) is hooked to the ICOM's phantom power( biased at 8 V)/microphone input. This is the reason for the output coupling Cap C4 being polarized as it is.
Originally Posted by AG3Y
To insure (low 1/f) noise the low noise TL-071 OP-Amp J-FET input provides the same advantage as the original ICOM electret mic circuit. When the pot (R1) around the OP-Amp is set to mid-range my dynamic microphone produces the same audio level as the original ICOM mic.
Last edited by AC0FP; 08-19-2010 at 08:51 PM.