Is low DC resistance good or bad for a mic? Is this Lav mic (CVM-WM300) incompatible with my mixer (Zoom PodTrak P4)?

Question

I'm pretty deep into debugging this. I suspect there's just some knowledge I'm missing.

The lav mic is a stereo 3.5mm TRS male from a wireless lav kit CVM-WM300. This mic is working for sure as I happily connect it directly to my computer. I connect the lav, without the wireless system, to either:

• DISINO 1/8 to XLR Male, to Balanced 3.5mm Female Stereo TRS Mini Jack
• COLICOLY XLR Male Balanced to 3.5mm Female Audio Converter Cable Adapter

Which plugs into the XLR inputs on the back of the Zoom PodTrak P4. I just hear noise. No signal from the mic.

I bought a multimeter and started measuring to see if the pins on the adapters are wired correctly. They do seem to be wired correctly per the diagrams I found. I measured the DC resistance on my Shure SM-57 to be 17 ohm, and the resistance on this Lav mic is 1 ohm. That's the same resistance I measure between the hot and cold signals on the XLR end of the adapter.

Everywhere I read that microphone's impedance should be in the 100-600 ohm. Which is nowhere near what I'm measuring.

So the question really is - is this 1 ohm completely wrong because it's a DC measurement? Is 1 ohm just so low impedance that the mixer can't handle it? Is there another reason that this lav mic is not working at all with the Zoom P4? Do I need another component to make them compatible?

Answer 1

Almost all lav mics work the same way. They require what is known as pip for plug-in-power, that is a voltage feed of around 5V. The P4 does not have any input giving this kind of power. You can get an adapter for this, I use Rode VXLR+ myself (NOTE: the + in the name, the version without + does not output pip). You use that connector or similar on an XLR input that outputs +48V and the adapter changes it to pip voltage around 5V.

The 1 Ohm you measure between the Hot and Cold on the CLR is probably a full short - which is correct. The pip microphone uses only two wires, one is the sleeve and the other is tip + ring.