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Author Topic: Radio pickup  (Read 1849 times)

gkippola

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Radio pickup
« on: May 22, 2012, 09:00:22 am »

I moved my studio to a new location late last year, what a task, but love the new one. In the new building I still have, slightly worse, a problem with my '55 Telefunken u47.  When it is hanging up on a large stand, if the cable is draped down the stand, i can hear a local fm radio station which is at 107.7 mhz -if i crank the gain waay up.   In the old location approx 15 mi away i used to get the same thing. The mic and NG PS are totally original, except i changed out the mic cable to gotham gac-7.  If i let the cable just hang loose w/o wrapping it around the stand in any way -it goes away.  Anyone have experience with a prob like this, as i haven't had the time yet to sort it out yet, it's otherwise working great. No other mics in the cabinet will do this-
I checked the internal wiring, and pins 3 and 6 are soldered together, and go to case and cable shield, but 4 goes to a separate ground wire--  i think the recommended way was to tie 3,4, and 6 together at the mic-is that recommended?
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klaus

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Re: Radio pickup
« Reply #1 on: May 23, 2012, 12:44:45 am »

RF in these mics is usually cured by rigorous application of a good (i.e. 100%) combined grounding /shielding coverage of all components involved.

Let's start by connecting pins #3, 4, and 6 together and to the Gotham cable's ground wire and cable shield - on BOTH cable connectors!

Also make sure that the XLR chassis-mounted connector on the U47 power supply is similarly grounded/shielded: its pin #1 should be connected to the shield of the internal cable going to the multi-pin Tuchel female on the p.s.


Please report back with the results.
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Klaus Heyne
German Masterworks®
www.GermanMasterworks.com

gkippola

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Re: Radio pickup
« Reply #2 on: May 29, 2012, 12:19:06 am »

So far, results are good,
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Jim Williams

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Re: Radio pickup
« Reply #3 on: May 29, 2012, 12:10:10 pm »

Clean the pins on the mic connector. Corrosion does build up after 50 years. Replace the connectors on the mic cables, you can't clean female pins easily so it's best to replace them.
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