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Author Topic: Impedance switch seems to have opened up KM85  (Read 1111 times)

frank w.scott

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Impedance switch seems to have opened up KM85
« on: November 02, 2005, 02:41:57 PM »

I've got a KM85 that has been running through an RNP8380 pre.  When I got the mic is was set at 50 ohms impedance.  I've been contemplating changing that to 200 ohms since I've been having to turn the pre up to 42 db to make it workable.  So I made the change today and it seems that my KM85 has either seen the light or there are some funny things going on with the KM85.

At 50 ohms the mic seemed overly muddy, in fact, I've been having to actually EQ some of the low end out of it, I've always thought that to be strange since it has a severe bass rolloff from 200 hz down.  Now after the switch no EQ required, in fact it just "feels" and sounds like one would imagine a KM85 to sound.  The top end has also opened up, or at least the less bass end has allowed the top to come out.  

It isn't bright, just very smooth and open.  I know there's been some discussion on whether impedance matters when the input has enough, but it seems to have worked in this one instance.  I'm running cable no more than 20 feet.  Maybe it's just an anamoly between the RNP and the KM85.

Regardless, I just thought I'd throw this out there.
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boogalaboogala

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Re: Impedance switch seems to have opened up KM85
« Reply #1 on: November 02, 2005, 04:51:35 PM »

I've read that, as a rule of thumb, the input impedance on a pre should be TEN TIMES the output impedance of the microphone.  Now, I only have five impedance settings on my pre, and I usually go to the setting below where a factor of one would be; but I've found it's often the case that this rule holds true.

Am I out of my mind?
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frank w.scott

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Re: Impedance switch seems to have opened up KM85
« Reply #2 on: November 02, 2005, 05:22:29 PM »

Well the RNP8380 has 5000 ohm input so it was more than equipped to handle the KM85 at 50 ohms.  

Perhaps too much input impedance causes distortion(in this case low freq anamolies)?  Or perhaps having to turn the RNP up to 42 db gain on a KM85 causes irregularities.

Hard to say, but the change in sound is most definate.
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