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David Waelder

Neumann mikes in radio boom

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I am a fan of the short Neumann microphones - the KMR 140, 150, 185 etc. They have served me well on many projects. Lately I have been noticing some noise when I use them in a quiet environment with a cordless boom configuration. They are very quiet - at least, quiet enough for movie work - when hard wired but there is an undertone of noise when hooked up to a radio transmitter. I can only describe this noise as a crackling hash. It is sufficiently background that I have successfully used the mikes outdoors, or in noisy interiors, without harm but it is disturbing when used indoors in a quiet environment.

At first I thought it was a problem with my radio transmitter or, possibly, interference from an on-cart IFB transmitter. Maybe one of the battery chargers I keep on the cart throws off some RF that I would notice only in a critical listening situation. Well, I ran some careful tests and I'm pretty sure it isn't any of those things. I have swapped out transmitters, receivers, locations of gear on the cart, mixing panels, antennae, etc. etc. I have used components in different combinations and different locations. I have simplified hook-ups, eliminating patch panels, using whip antennae directly on the receivers, etc. I have pulled all AC power delivered to the cart with no effect. I have exchanged phantom power supplies and also measured voltage at the terminals (52 volts with no load) and eliminated those as culprits. So, with all these tests, I am confident that it's not:

the transmitter (Lectro 200 series & 400 series)

the phantom power supply

the receiver

the antenna

the position of the receiver on the cart

whether other elements are operating on the cart

whether or not AC power is delivered to the cart

which mixing panel is in use

No matter how I configure things, the short Neumanns (I tested 2) make noise and a longer Neumann (KMR 81) is quiet. It's a consistent pattern.

One of those Neumanns was recently in Connecticut to correct a problem with susceptibility to RF interference. The service shop put in a new circuit board so it is fitted with the very latest electrical design. (And, by the way, has been very RF resistant ever since.)

So, my question to the group is: How do I proceed now?

One obvious solution is to purchase a pair of the new Sennheiser 8050s (or a pair of MKH 50s or one 8050 and one 8040). I am seriously considering this or some variation. But that's an expensive solution and I want to make some investigation before going that route.

Has anyone else experienced this problem?

Is there a reasonable solution? Possibly some sort of filter trap in the cable from the transmitter?

Thanks for your help. (& sorry for the long post)

David Waelder

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Hey David,

its been a long time since your post, but I have a similar problem with my kmr 185’s. I can’t use them wireless in quiet indoor places.

I use the lectrosonics plugon or a ssm with 48V supply.

did you find a solution for that?

thanks

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Regrettably, I never did identify the cause of the noise I heard with some Neumann mikes in a radio boom situation. I did learn that the shotguns (KMR 81 & KMR 82) are electronically different than the shorter mikes but I don't recall how they differ. The Audio Ltd device is probably worth a try but I'm not sure that the noise came from RF interference. Rather, I think it was some sort of incompatibility between the components. But, worth a try.

 

I acquired a set of Sennheiser 8050's and the mysterious noise problem was never heard from again.

 

David

 

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I gave up using my km185 because it was too noisy for quiet talkers (hard wired). My kmr81 would buzz around fluro lighting, otherwise I loved the sound of the neumanns. They both were stolen a few years ago and replaced with a mkh50/dpa 4017, I use the mkh50 probably 90% of the time now.  

 

Grant.

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just plug the mic hard wire to the recorder ,and then turn on other suspect one by one ,You then find which one causing interference or it is self noise of the boom transmitter  

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I have also had problems with a KM150 for wireless boom. With a Lectro butt-plug the KM150 didn't work at all. I needed a phase reversal adaptor to make it work. I believe it's because my older KM150 is pin 1 hot. With a Sony UWP-D plug on TX the KM150 worked fine, but I did get occasional RF "hash" in some circumstances. works just fine hard wired. My MKH8060 has zero problems with plug ons of any stripe.

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1 hour ago, chrisnewton said:

I needed a phase reversal adaptor to make it work


Yes, that’s a known issue with the Neumann mikes. However, it doesn’t seem to be related to the noise issue. That seems to be some sort of incompatibility between circuits but the particulars remain a mystery. (At least to me)

 

This problem was one of the reasons I stopped using phantom power supplies, like the Denecke 48v unit, in favor of the Sound Devices MM series preamps. 
 

At a distance of a dozen years I no longer accurately remember the sequence of attempted remedies. I’m not sure if use of MM preamps was a remedy or if the issue wasn’t resolved until I acquired the Sennheiser 8050’s. 
 

David 

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