Canon XM2: Wireless Lavalier Mic Question

[Acid5]

Hi

I have recently purchased a Trantex S4.4 Wireless Lavalier Microphone system for recording selected audio at wedding events.

I can't afford a £400+ Sennheiser kit at the moment, but this cheaper model comes with recommendations.

To my dismay, the receiver appears to be mains operated only - DC11-18v IN/100A. So the first issue is finding a plug socket near the camera on the day.

My main concern however, is plugging this receiver into my camera [Canon XM2/GL2]. I am assuming it is safe to do so?

It doesn't say anything about video cameras in the instruction manual [it mentions amplifiers], but I am assuming such a piece of audio equipment is designed for video camera mic input as one possible use?

I often plug in my external shotgun microphone into my XM2, which is itself powered by a battery. This wireless lavalier is mains, however, and I want to be 100% sure before I connect the electric-powered receiver to my camera via the external mic jack.

I vaguely remember learning about 'phantom power' and '+xx volts' for plugging in differently powered microphone systems, but I'm currently rather unsure about this area [the XM2 has one simple external mic jack, described as 'MIC terminal input 3.5mm stereo mini-jack -35 dBV (with 600 ohm mic)/5.6 kohms', and there is nothing about plugging in various mic types in the manual].

Any technical types able to offer me some advice here, or videographers etc?

Thank you

 

[rogs]

First thing - you say the mic receiver requires '11 to 18VIN/100A'. I would hope not -- that's the sort of power required to crank a car engine!

I suspect it's more like 11 to 18V @100mA (that's milliamps) --1000th of the power!

If that's the case, then you could use battery power -although you might need to use a fair sized battery pack, if you want to run for any length of time. A 12V SLA (Sealed Lead Acid) battery would be ideal - although there may be suitable Li-ion battery packs avialable these days - I'll leave it to the power supply experts to comment on that one.

When it comes to 'phantom power' there are two quite distinct types. Most professional condenser mics require a 48V phantom power supply from the mic input itself. If your XM2 mic inputs use XLR connectors, then it's possible the camera has that facility, but it will be clearly marked, and switchable.

If the camera uses 3.5mm 'minijack' mic inputs, then it won't supply 48V phantom power.

What it may supply is 'plug in power'. This is where an electret mic can receive the power it requires, instead of mounting an internal battery in the microphone. In this case, the voltage is only 1.5V, and the current very small as well.

Strictly speaking, you should make sure that plugging in an input, that doesn't use 'plug in power', should be 'capacitively isolated' to prevent the D.C.power from the camera input jack being fed into the receiver output, but in practice, it almost certainly won't make any difference.

I see you have already said you plug your shotgun mic, which has it's own battery, into the socket with no ill effects, so I can't see any problem with the receiver jack plug.
(I'm assuming we are talking about 3.5 mini jack sockets here - not the XLR ytype I mentioned above).

If you do decide to power the receiver from the mains, I'm assuming that the receiver is fitted with a socket marked '11 to 18V DC in', or something similar, and that you are supplied with a plug in 'wall wart' type power supply to step down and isolate the mains. The isolation transformer inside that power supply will ensure you have nothing to fear, safety wise.

 

[Acid5]

Thank you for your quick and helpful reply, rogs.

I have checked the mic receiver again and yes, it says 'DC 11-18V IN 100mA'

I'm a noob on power supply aspects, so I really wanted to make sure that plugging something connected to the electricity into my camera wasn't going to blow it up.

I see that there are SLA batteries for about £15, with about same again for a charger. Shame they are so big to haul around - the Sennheiser wireless lavalier I borrowed a while ago had a compact receiver with just a square 9v square battery inside - but I guess I shouldn't complain for such a reasonably priced UHF radio mic.

"When it comes to 'phantom power' there are two quite distinct types. Most professional condenser mics require a 48V phantom power supply from the mic input itself. If your XM2 mic inputs use XLR connectors, then it's possible the camera has that facility, but it will be clearly marked, and switchable. If the camera uses 3.5mm 'minijack' mic inputs, then it won't supply 48V phantom power"

I remember a few years ago using a professional DV camera with 'MIC' and '+48V' switches, the mics connecting via XLRs. On my much smaller XM2, I have only a 3.5mm jack input with no such options.

Have no idea about 'plugin power' through my camera mic socket. I found a little information here [XM2 = GL2]:-

GL2 and plug-in power? - The Digital Video Information Network

The Rode shotgun mic I received in the package with my camera is obviously suited to the XM2, and that needs a battery to run.

"If you do decide to power the receiver from the mains, I'm assuming that the receiver is fitted with a socket marked '11 to 18V DC in', or something similar, and that you are supplied with a plug in 'wall wart' type power supply to step down and isolate the mains. The isolation transformer inside that power supply will ensure you have nothing to fear, safety wise"

I was supplied with a Trantec Systems power supply. It says on the plug: class 2 transformer, input 230VAC 50hz 9VA, output 13VDC 300mA - so I'm assuming this gives me all the correct electrical current and safety I need for this situation.

Just ran a test on my guinea pig old palmcorder, and the mic works a treat - I guess I'll assume all will be OK with my XM2. Shame no helpful information in the manual for either the camera or the mic about connecting up both pieces of equipment, at least in terms of power supplies.

 

[Acid5]

"What it may supply is 'plug in power'. This is where an electret mic can receive the power it requires, instead of mounting an internal battery in the microphone. In this case, the voltage is only 1.5V, and the current very small as well.

Strictly speaking, you should make sure that plugging in an input, that doesn't use 'plug in power', should be 'capacitively isolated' to prevent the D.C.power from the camera input jack being fed into the receiver output, but in practice, it almost certainly won't make any difference"

I've just noticed my guinea pig palcorder external mic socket says 'PLUG IN POWER'.

However as far as I am aware my XM2 is not plug in power, unless anyone knows any different. One person in the thread I linked to above says his plug in power microphone gave no sound when he tried it in the XM2s mic jack, indicating it is not. And I'm sure it doesn't have phantom power either.

I've just tested the wireless mic in my XM2, and all seems fine - good clear sound reproduction through the headphones when I manually adjust the camera's audio levels [or rather level, since I get a left channel only on this one - mono mic I guess].

So when I tested it through the [apparently] plug in power mic socket of the old palmcorder, I haven't risked any damage to that camera or my new receiver have I? Will my mic receiver likely be 'capacitively isolated' to stop any DC power being fed into the receiver output, as you mentioned above?

I did notice the radio mic pickup through the palmcorder was rather loud, but this old camera has only automatic audio recording levels so it was hard to tell if there was any conflicting going on.

 

[Acid5]

This is my wireless mic, lavalier version:-

http://www.trantec.co.uk/html/p_UHF_Systems_S4_4.htm

Sorry for extra posts, but I really need to get to the bottom of this today with the job tomorrow - here is latest research I have done today:-

- According to the retail supplier of my wireless mic, the plug in receiver "will be line level output"

- My Canon XM2 is apparently mic level input. It is 3.5mm jack [not XLR so no danger of phantom power from camera].

I understand 'line level' = 'plug in power'?

Tests I have done:-

- Plugged receiver into my old JVC palmcorder - the mic input on this says 'plug in power' [i.e. line level]. Results: mic works, though output from camera seems very loud. However this old palmcorder has no manual audio level controls

- Plugged receiver into my XM2 - the mic input is apparently 'mic level'. Results: mic works, with output from camera rather loud but clear - I have audio level controls on this camera so when I have it turned down to the lower end, with the lavalier mic attached just below chest level, I get good speech sound

So... I have a mains-powered apparently 'line level' mic receiver working through both a 'plug in powered' external mic jack, and a different 'mic powered' mic jack, with the results sounding better through the 'mic powered' jack.

But isn't this at odds with how it should be? If anything, I would guess that if the mic receiver is actually working more correctly through the 'mic level' XM2 than it is through the 'line level' JVC. It is difficult to say if there is 'too much' loudness through either camera, since both seem very sensitive machines to sound with audio recording levels on the XM2 rarely needing to approach halfway from past experience with my external shotgun.

I'm tempted to throw caution to the wind and just go for it tomorrow by plugging the receiver into the XM2, but I am concerned about possibly damaging any circuitry by plugging a 'line level' into the 'mic level'.

I can say that my XM2 test did not seem to distort mind you - it seemed loud and clear through my headphones.

I really need to get to the bottom of this today, so would be extremely grateful for any further help and information.

Some info I found about the XM2 mic jack: XM2 Audio Line Input while filming - The Digital Video Information Network

 

[rogs]

I understand 'line level' = 'plug in power'?

No - the two phrases have nothing to do with each other!

'Plug in power' is merely the provision of a low voltage, low current phantom DC power for suitable electret mics.

'Line level' refers to the sensitivity required to match audio signal inputs and outputs together.

A 'mic level' input will typically be about 40dB more sensitive than a 'line level' input (40dB represents about 100 times more in this instance.)

It is unusual for radio mic receivers to provide only a line level output - in many cases they are likely to simply be replacing a standard microphone, and are going to use the same amplifier or mixer input, but it is possible I suppose. I'm not familiar with the model you describe, I'm afraid.

What is also possible is that you may have the option to make the two 'match',if you have control of both input and output levels.
With the receiver on it's lower settings, the output is going to look more like a mic level signal, and with the XM2 adjustable input levels set near their minimum, that is going to look more like a line input!

Not a perfect solution, and you may find you don't have enough 'headroom' (that is, spare sensitivity, before the signal clips and distorts).you'll have to experiment and see. That is the most obvious shortcoming.

From a damage point of view, I really don't think you're likely to do any. Signal level mis-matches may distort a signal, but they are too low an energy signal to casue any actual harm to equipment.

Damage from 'plug in power' DC is theoretically possible, but really only if you plug a dynamic microphone, with no internal coupling transformer, directly in to the offending input.
In your case you should be OK on that front.

Ideally, if your receiver does only have a line level output, you really need to 'pad' the signal level down to match the XM2 input more exactly, and give you extra headroom. Such a 'pad' is only a passive (resistor network) attenuator. You can Google 'audio pads' for loads of information on these devices.