The Panasonic DWM-MS2 condenser microphone has a 3.5mm TRRS plug that connects to the GH3/GH4 body http://www.bhphotovideo.com/c/product/907000-REG/Panasonic_dmw_ms2_External_Stereo_Mic_For.html

Similarly, the iRig PRE XLR microphone interface also has a 3.5mm TRRS plug http://www.bhphotovideo.com/c/product/840641-REG/IK_Multimedia_IP_IRIG_PRE_IN_iRig_Pre_Microphone_Interface.html

I wondered if I could use the iRig PRE as an XLR input, pre amp & +48v phantom power source for my Apex420 condenser microphone when connected to a GH4. I decided to roll the dice & connect the iRig PRE directly to a GH4 (via the 3.5mm mic input) for further investigation. DISCLAIMER: I am not an audio engineer. Please take that fact into consideration. I'm not affiliated with IK Multimedia in anyway (the makers of the iRig PRE). I simply saw (what appeared to be) the same 3.5mm TRRS plug between the two aforementioned devices & wanted to see if I could utilize some of the audio gear I already own. I was stoked to discover that I could record video & stereo audio directly to my SDHC card using this setup. The SNR & noise floor (with the iRig's pre amp turned up to 1/3 gain) sounded acceptable for my video/stereo audio recording purposes. Your personal view might differ & I respect that. More testing is needed to determine whether the iRig PRE is a pro-sumer audio solution or a professional audio solution for the GH4.

SIDE NOTE: the iRig PRE I’m using is NOT hacked. I connected my Apex420 to an XLR cable -> XLR cable to the iRig PRE–> iRig PRE 3.5mm TRRS plug to the GH4 3.5mm mic input. The iRig's pre amp was turned up to 1/3 gain. After connecting all of the cabling I tweaked a couple of settings within the “Motion picture” menu tab (page 6) as follows:

Mic Level Adj.: 0

Special Mic -> Manual -> Mic. Directivity Adjust: adjusted to the right side of the scale (cardioid) -> set. All special mike modes worked excluding the “stereo” setting.

Mic Level Limiter: On

The previous setup worked for me & I hope a similar setup utilizing the iRig PRE & GH4 works for you too. Please post your findings/gear setup/audio menu settings here.