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Jim Loomis
wireless distortion mystery
on Apr 4, 2008 at 10:22:49 am



I have a mystery I would like to share. I have set up an audio system to go wireless from a mixer to camera that goes like this...

a Sennheiser 416 running XLR down the boom into a Marenius MM-3100 Mono Mixer. From the mixer I have a Sennheiser SKP 500G2 transmitter sending out to a Sennheiser EK 500G2 reciever going into the camera.

A mic – XLR cable – mixer – transmitter – reciever – camera setup to summarise.

In this setup I get low level distortion on the receiver end of the chain. (I have hard wired, & cut the mixer out of the equation in tests & all is beautifully clean) Whilst testing, however, I discovered that if I activate the Battery Test function on the mixer the distortion disappears & I receive a clean signal from the receiver & the camera.

I would be very interested to hear if any one

A. Understands what I just wrote – is it intelligible?

B. Has any ideas as to what it is related to the Battery Test function of the mixer that is interfering with the transmition?

Could it be attenuation or power usage?

In tests I get the same distortion whether the Phantom power is on or off on the transmitter.

Any thoughts would be greatly appreciated.

Many thanks


Jim Loomis
jim@shotcuts.es

http://www.shotcuts.es
http://www.loomisimages.com


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Ty Ford
Re: wireless distortion mystery
on Apr 4, 2008 at 1:04:44 pm

Hello Jim and welcome to the Cow Audio Forum,

You have done some good problem solving. You pretty much have your answer, it's the mixer.

Now, why?

Do you have the 48 V DC option for the mixer? If not, the likely cause is the 18 V DC Phantom Power voltage. Sennheiser 416 mics require 48 V DC Phantom Power. If they don't get it, they sound distorted because they are power starved.

Even if you do have the 48 V DC option, the power supply may not have the current to power the 416 properly. Power of any sort is a function of voltage and current - actually power TIMES current. The formula is P=IE; where P is power, I is current and E is voltage.

There are outboard, battery-powered Phantom Power supplies that do supply 48 V DC at a current level high enough to power the MKH 416.

If you were paying me to consult with your on your sound package, I would spec the Sound Devices 302 mixer to replace the Marenius. If your transmitter can take line level input, the Sound Devices MixPre works. It's lighter and is more easily belt mounted than the 302. BTW, I've never heard of Marenius. Thanks for letting us know about them.

Regards,

Ty Ford






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