Strange issue with M8 wireless microphone

malc c

I'm hoping someone can explain why the following issue is happening.

I have a Panasonic HC-VX870 4K camcorder which I'm really happy with.  For general use where I want to record two people talking to camera  I often use a pair of wired lapel microphones, connected to a Rode 2-1 adaptor which then connects to the camcorder's mic in socket.  The mics are TRRS and came with TRRS to TRS adaptors, and as the Rode SC-6 adaptor is also TRRS the mics are plugged directly into it and then a TRRS to TRS adaptor cable connects the SC-6 to the camcorder.  This works perfectly and both microphones are picked up and I have no issues with the sound balance between the two.

For sessions or locations where a cabled microphone is impractical I have a K&F M8 wireless microphone set up.  This is the typical transmitter unit that clips to a belt, with a plug in TS mono microphone.  The receiver sits on the camera via a cold shoe, and the output to the camera's mic socket is connected via a short male TRS to male TRS cable.  Again this woks a treat.

However I now have a project where I need to use the wireless set up and a wired lapel mic together.  So I connected a TRRS lapel microphone to the SC-6, connected a Rode SC-7 TRS to TRRS cable between the receiver and the SC-6 adaptor, and then the SC-6 to the camera via a TRRS to TRS cable adaptor.  With the wireless TX and RX off the lapel mic works fine, but as soon as I turn the TX and RX of the wireless set up on the wired mic is taken out and only the wireless mic can be heard.

I've tried various combinations and adaptors, but the same happens each time.  The wireless units are powered by 2x AA batteries, so it's not as if there is 48v phantom power involved.  The camera's 5v power for condenser mics is ample enough as it works just fine when just the two lapel microphones are connected, so that can't be the cause ?

Any suggestions would be welcome.....

noiseboy72

What's probably happening is that the source impedance of the radio mic receiver is much lower than that of the lapel mic and as you turn it on, it essentially shorts out the lapel mic so nothing can be heard. the radio mic is probably also a lot louder than the lapel and the camera's auto-gain control is compensating for this.

I would suggest a Tascam or Zoom external recorder and sync the audio back up in the edit. Another method would be a small mixer to combine the signals prior to the camera, but you might need to attenuate the signal prior to the camera connection.

Terfyn

The problem will probably be in the SC-6. I suggest you look at cam mixers such as Saramonic.
Or you could just try a dual mono socket to stereo jack splitter cable.

Certainly, as Noiseboy72 says, there is a power imbalance between a lapel mic with no amplification and a wireless mic which will certainly be powered.

My own solution would be my Tascam DR-60D MkII.  I would use the 1 & 2 inputs with 3.5mm to 6.3mm adapters and balance the source signal in the recorder. The DR-60D has a feed directly into the cam mic input socket.

malc c

Thanks for the replies.  I've ordered a 3.5mm TRS to two mono sockets cable to see if that will at least give the the opportunity of recording on different channels, which I can live with.  Funds won't stretch to the DR60

12harry

Hi, seems a shame as you are nearly there.... however, without solving the impedance and/or levels ( as suggested prior), I don't see that things won't be much the same. I suspect you need to attenuate the radio-mic output - something as simple a 1000-ohm resistor in series, may do... if not, then increase with more the same.
Those tie-clip mics have an op-Amp buffer ( hence the need for some battery power )...The other possibility is the Radio-mic is such a low o/p impedance it's draining the (limited) power that the camcorder produces on the Mic-input.  If you have a digital voltmeter you can check what DC Bias is available for the Tie-Clip - their needs vary quite a lot....from 1.5 - 3.5v
FWIW
Your set-up is quite complex, but I guess I understand it....Are you plugging only a cable into the camcorder?  
With modern surface-mount construction the sockets are very delicate and a short-length of mic-cable wound round something, will ensure you don't strain the camera-connector when attaching external kit.

As with many things in Life, . . . . it's not What you do, . . . rather How you do it...
It might be sensible to discuss this issue with a local electronics repair shop.  You probably require two Mic inputs  ( if paying include a Line-In for later-on ), One for the (?) high-level Radio-mic receiver and the other for the Tie-clip.  Ideally both will have some attenuation options, either in switched-step, variable, or simple Hi-Lo - with the Radio-receiver having a blocking capacitor so it can upset the tie-clip's power source......but they may need to "play" with your Kit, to solve this issue.
I'm fairly sure it's not RF interference, but you could try removing both the transmitter and receiver batteries, whist still plugged-into the camcorder - this should not change "much" - hope that helps.

Good Luck

malc c

Thanks for the info.  Placing an unwired stereo (TRS) 3.5mm plug into the socket on the camcorder I measured 2.79v DC between both sleeve and ring and sleeve and tip.  But I'm assuming the wireless set up wouldn't be bothered about that as it's the only component that is powered by an independent source (2 x AA batteries).
Edit: - just measured across the output from the RX and it's 1.42v on the tip and ring

Hopefully the adaptor I just ordered will arrive early tomorrow (its confirmed next day from Amazon) and it will at least give me an option as I need this for tomorrow afternoon !

I don't do much with the camera that would warrant having it modified for additional sockets.  Normally I use it for videoing / vlogging trains etc.  But on this occasion I need to interview people behind exhibition stands so need the wireless side as having cables trailing in an exhibition hall isn't practical.

Its all good fun

malc c

Hope the attached drawing explains things better.  The setup on the left works, the one on the right doesn't

                                                                       

malc c

This is what I'm planning to test when the stereo to individual L/R Channel cable arrives

                                                                       

noiseboy72

I think this will confuse the gain control on the camcorder, as the levels will be very different.

A 25db reduction should be about right. One of these: Sescom3.5 mm Line to Mic -25 dB Audio Cable for Zoom H6 (9 would be perfect and I think would solve your problem.

malc c

Thanks for the suggestion, but why don't I need any attenuation when I use just the wireless mic, with the camera set to manual record levels ?