Phantom Power and Wireless receivers?
 

Today I had to video a conference using my precious wireless Sennheiser lapel mics and once set up for testing the audio guy wondered where a huge amount of hum is coming from...

He had phantom power turned ON!

I don't know if that could have damaged the wireless receivers that were receiving 48V, but they seem to work ok - thank god.

Do you think this can cause damage or are the circuits designed to 'handle' that?

The model of receiver is EM100 from the evolution wireless Series ew100.

Jack

Jack,

are you running an unbalanced connection between the Sennheiser receiver (which would have to be the XLR, not the phone connector for this receiver) and the audio guy's input? Had it been balanced, you shouldn't have had a problem with hum or anything like that.

What I am wondering is why you were going into a mic input in the first place. Your ew100-series wireless receiver outputs a line signal, and that's what I would feed into the audio recording equipment, and phantom power only applies to mic inputs.

I don't have the book at hand to confirm it, but I seem to remember that Jay Rose described phantom power such that it only does something when a device is actually "looking" for it. Sorry about the not-so-scientific wording, I'll try to look it up tonight and confirm this. But this is true for balanced connections only.

If you go to Shure's website, they have a PDF file that you can download called "Audio Systems Guide for Video Production"; it talks a little bit about phantom power and balanced/unbalanced connections. They don't use a wireless mic such as yours as an example, but a dynamic mic (which needs no phantom power either) and state that it should work fine with phantom power turned on and a balanced connection, but a hum could result from phantom power turnd on with an unbalanced connection. Seems similar to what you experienced.

- Martin

I can draw circuits which would sustain damage and I can draw ones which are immune. If the device were coming out of my shop you can be sure it would be one of the latter that went with the product. Thus I'd take the fact that no damage was observed put together with Sennheisers years of experience in the field and the frequency with which things like this happen to conclude that you are protected.

Still researching this, I found that as per the wikipedia article (http://en.wikipedia.org/wiki/Phantom_power) it states;

"Phantom Power's supply voltage is effectively invisible to any balanced
microphones" which confirms what Martin said.

However the dilemma... as per the wireless receiver's specifications in the manual (page 81) it states;

"AF OUT: 3.5 mm jack socket = unbalanced: +10 dBu"

(As you may know, this is the only output on the body pack receiver, but it does indeed end up as XLR for connecting to the actual mixer). I always thought any XLR connection is balanced but not in this scenario!?

So that is most likely to have caused the huge amount of hum and which makes the circuit not 'immune' but hopefully 'sustained damage'.

I have emailed Sennheiser USA for more factual feedback...

Sorry, I missed this detail. I don't have a bodypack receiver, but the regular one which offers a balanced XLR in addition to an unbalanced phone connector.

No, a simple adapter will just connect the pins but not balance the signal. The results may or may not work, as you have experienced. There is, however, the option of using a balancing transformer that would turn your wireless receiver's unbalanced output into a balanced signal.

- Martin

Replies from Sennheiser
 

Just to follow up, I have got 2 replies...

-------------------------------------------------
REPLY 1 - from Syntec (Australian Distributor for Sennheiser):
December 11, 2006

"The receiver's output circuitry is design to block up to 63V coming into its output connector.

Thus, the 48V of phantom powering supplied by the console should not be a problem.

However, when a mixing console develops a fault (i.e. 48V becomes not clear or not within phantom powering design tolerance) or the protection components in our receiver fail then the output of the EM100 can become unstable and unpredictable in operation.

Best regards,
Syntec Service Department"

-------------------------------------------------
REPLY 2 - Sennheiser USA:
January 17, 2007

"There is protection built into our receivers so it should not have hurt anything. If for some reason they start to sound noisy send them in and we'll take care of it under warranty."

-------------------------------------------------

So I'm glad that the circuit has a tolerance to accidental phantom power, Martin P. thanks for the advice regarding the balancing transformer... handy to know.

Jack

Hang on, in your first post you referred to the receiver as being an EM100, which is the rack-mount or table-top diversity reveiver. It does indeed have both line and mic level outpus and they're available on either XLR-M balanced or 3.5mm TS unbalanced outputs. In a later post you talk about the bodypack receiver, which does only have the 3.5mm jack. Which are you using?

EK100 - The bodypack receiver
 

Yeah it's the EK100 - The bodypack receiver, I got the model numbers confused and also it's not the G2 (Generation 2) as you see everywhere now.

Here is the link to a brochure;

http://buy.sennheiserusa.com/ASP/Sen.../100series.pdf - 762KB, 2 pages.

Regards,
Jack

most of these recievers do have protection against ph power
not as some mixers which can be damaged if you run phantom inside of it channels ( usually unprotected unbalance outs)
usually it will not affect on the quality of the signal that comes from your reciever
the 100 has unbalanced out even it comes as 3 pin out