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Author Topic: U87 and TLM 103 noise  (Read 2440 times)

underdub

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U87 and TLM 103 noise
« on: April 13, 2012, 12:50:11 pm »

Hey all,

I have a pair of old U87s and a TLM 103 that are very noisy.  It's a hiss type noise, similar to the gain of a preamp turned all the way up.  I have tried different preamps, patch points, etc.  It is common to these 3 microphones.  When I switch to other mics, the channel is dead quiet.

 i.e., I can setup an 87, get a good recording level and hear the noise loudly.  Unplug the 87, plug in a 4033, U95 or other, change no other settings and get roughly the same signal with no detectible noise. 

I thought the 87s were just getting old and needed some attention, but now that the TLM 103 is doing the same thing, I'm baffled. Could it be oxidation on the connectors, or somewhere inside the mic?

Thanks,

Travis 
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klaus

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Re: U87 and TLM 103 noise
« Reply #1 on: April 13, 2012, 01:10:44 pm »

Troubleshooting more than one component at a time, in your case three mics, can be a mental and technical challenge. As soon as a second or third item is used as comparator, the assumption is usually: "This one is healthy, so the other one must be defective!"

First, an AT4033 should not be quieter than the two Neumann models you mention, especially not when compared with a super-quiet model like the TLM103.
So, it is possible, but would be a rare circumstance, that all three microphones are defective, or that, equally likely, something has gone haywire in your signal path downstream from the mics.

Here is what I would do: establish a baseline: borrow a well-working U87. Position U87 (proven as good) and U87 (possibly defective) next to each other. Singing a steady tone, set gain to similar levels at the board. Now, with no input into the mics, crank the monitor level of the board  to compare noise floor of both mics.

This will be the first objective and useful troubleshooting test of several to follow.

Let's say, the U87 (possibly defective) has indeed a 6dB or higher noise level than U87 (good). That still could indicate a healthy U87, if it's one of those U.S.-delivery U87s (some came with as much as 12dB lower gain!) You would need to consult your schematic and check whether pads and 50 Ohm strapping are in place in your mic, and bridged pads and 200 Ohm strapping are found in the "good" mic.

The U87 issue is completely different from the TLM 103 issue which shares NONE of the components and circuitry of the U87, old or new style. Here, again, I suggest comparing noise floors with another TLM103 by borrowing, or buying one on try-out. If your mic turns out defective, only Neumann/Sennheiser have the parts and circuit information for repair.

Best of luck,
KH

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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

radiovinhet

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Re: U87 and TLM 103 noise
« Reply #2 on: April 14, 2012, 09:57:17 am »

Can you upload some mp3 samples from this mics?
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underdub

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Re: U87 and TLM 103 noise
« Reply #3 on: April 21, 2012, 02:44:03 pm »

Thanks for the advice Klaus.  When I get back to the studio I'll perform the tests as you describe and report my findings. 

I'll also upload an .mp3, but if I hear my noise used on the inevitable Waves U87 plugin model, I'm gonna be disappointed!  ;)
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