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Adam White

Squealing Neumann KM185

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Hey friends. 

Sent my KM185 in for repair because it was squealing like this. See attached. 

 

They sent it it back saying they couldn’t replicate the problem.  

I was having no problem that day on set though!

 

Humidity or weird RF? This unit was supposedly manufactured after the latest revision but it’s the only things I can think that would be intermittent. 

 

Cheers

Adam

neumann_km185_hissing.wav

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Could be the 48v power in what ever the mic is plugged into. The tone bursts are a bit surprising. If you can't recreate the problem then chalk it up to a one time thing.

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1 hour ago, Eric Toline said:

Could be the 48v power in what ever the mic is plugged into. The tone bursts are a bit surprising. If you can't recreate the problem then chalk it up to a one time thing.

 

Never had a problem with another mic. It’s  plugged in to a 633...

So weird! 

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I can‘t listen to this on my phone, but weird RF is always a possibility, especially with Neumann mics. 

I have great trouble with my KMR81i with the tx next to the mic on the boom. The mic has no rf protection and Neumann said they won’t do it, either. Maybe a similar issue with your mic?

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38 minutes ago, INARI said:

Does not it scream when connected to another device?

Sennheiser returned it to me but I won’t have a chance to test again for a couple of weeks. 

Thanks everyone for the notes.

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The KM 180 series uses a DC converter to boost the 48-Volt phantom supply voltage up to 60 Volts to polarize the capsule. The converter basically is a radio frequency oscillator that drives a tiny step-up transformer; its output is then rectified and smoothed.

 

With proper powering and a properly functioning microphone, the frequency of that oscillator is well above the audio range. However, if the microphone is defective or the phantom powering isn't up to specification, the oscillator frequency can dip down into the audible range. You can hear this if you connect the mike to an outboard phantom supply, run it for a minute, then turn the powering off while you continue listening to the microphone's output. As the stored energy in the supply and the microphone ebbs away, the oscillator will drop in frequency, and you will hear it descend through the audible range until it dies out completely.

 

Since Sennheiser didn't find any problem with the microphone itself, I suspect that it wasn't being powered correctly when you ran it. There have been two different versions of the KM 180-series circuitry; the changeover occurred around 2002. The original KM 180-series microphones required 2.3 mA; the later version requires 3.2 mA (in return for which they are 3 dB quieter, while keeping the same sensitivity and maximum SPL).

 

I suggest that you try your microphone with a different preamp, mixer or recorder, or with a known good outboard 48-Volt phantom power supply. The original version of the phantom powering standard set 2 mA as the recommended limit, and a lot of older equipment (and even some that's newer) falls out of spec trying to deliver the 3 to 5 mA that microphones commonly require today, let alone the 7 to 8 mA required in some extreme cases.

 

--best regards

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@DSatz thanks for the detailed reply. 

 

Update:

I wasn’t crazy. I had someone at the local shop replicate the problem with me, and sent it back in for repair for a second time.  It was highly unlikely that the 48v supplied was the problem as we used multiple preamps to test. 

This time the sennheiser technician heard the problem and repaired it. He wasn’t on his lunch break. 

 

I’m afraid I didn’t ask for their detailed repair procedure in the end... I just needed to get back to work!

 

cheers

adam

 

 

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Another update: The mic that was misbehaving last summer, squealing and what not, has been malfunctioning now in humid environments. And I'm not talking jungles, but a rainy days in Toronto. The noise floor comes up and things get crackly etc.

 

Seems to clear once the air dries it out again.

 

Do we have any KM185 users here that can speak to its "tropical" performance? Is another repair/cleaning in order or is failure expected in humidity for this microphone? 

 

AW

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Very weird. I too have been using Neumann's for years (KMR81i, KM140, KM150) and have never come across this, and I work in Vancouver. Officially this is a rain forest area. Lots of moisture here. Sorry if you were already asked this, but do you have access to another KM185? Curious if another one does the same thing.

 

CRAIG

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Adam, you asked many questions but did not share the repair info that took place at Sennheiser. A simple phone call to the Service Department 

there could give you the info about what was done to your mic and potentially help others on this board.

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1 hour ago, Ontariosound said:

Adam, you asked many questions but did not share the repair info that took place at Sennheiser. A simple phone call to the Service Department 

there could give you the info about what was done to your mic and potentially help others on this board.

Hey!

Thanks everyone for your responses.

It's currently in the Sennheiser shop and I think it's getting a new pcb, at a cost of around $350. I will be calling them next week to get the full story.

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