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While this post is written with the UR6QW processor in mind, it contains information which is widely applicable. There is some concern about connecting dynamic microphones to devices which commonly use electret condenser microphones. I believe this requires some clarification.

Electret condenser microphones generally require about 3 to 5 volts DC to supply an internal FET which acts as an impedance transformer between the electret element and the output signal line. The current supplied to the jack is usually limited via a resistor in the supply network. 2.2k is a popular value, which limits the current to 1 to 2 mA. This is sometimes called “phantom power”, although the real phantom power which gets used in recording studios is 12, 24, or 48 volts, depending on the standard used. Google IEC 61938:2013 for more information on that. Don’t try to power your electret condenser microphone with real phantom power!

The main question is usually “can I use a dynamic microphone plugged into a jack which usually drives an electret microphone?“.

Always check the schematic or ask the manufacturer first, but generally, yes you can. Having a DC bias of a couple of milliamps on your dynamic microphone element won’t hurt it, but may change its properties slightly. It may change the output level, or the frequency response, add distortion, or affect it in some other way. The key is to just try it and see. The good news is that due to the current limiting resistor in the supply line to the microphone, there should be no damage to the dynamic microphone. UR6QW himself says that you can use a dynamic microphone in the front MIC jack without installing a DC blocking capacitor, however, should you want to install one anyway, see the end of this post.

Recommended Reading (see myth #7)

Installing a DC blocking capacitor

Personally, I chose to install a 10µF / 16V electrolyic capacitor in my UR6QW processor, in the signal/power line, right behind the front MIC jack. This allows me to use a dynamic microphone with no electret current applied to it. The electret current is still available on the ICOM microphone jack if I want to use the stock mike.

Click the following image for a full-size view. Credit for the original image goes to NG7M (saved me from taking mine apart again!)

Installing a DC blocking capacitor

I did a complete review of the UR6QW processor right here.

I also covered my setup and settings using the UR6QW processor with my Icom IC-7300 here.

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Andrew - KD5FHW

I see you put the capacitor on the headset mic input jack. Will that take care of the 8-pin input in the front as well? I’m looking at using a low impedance (150 Ohm) dynamic mic through the 8-pin input with a Heil cable. Will I have any issues with the lower impedance mic? Thanks!