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Old November 14th, 2002, 11:56 AM   #1
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Do I need Attenuator?

I am in kind of desparate situation here so I am posting qustion everywhere. I want to know if I want to connect KM201 microphone to minidisk via phantom powersupply, do I need to put signal through attenuator? If so I want to know if the inline attenuator from Shure would do the job. people from fullcompass.com told me that those wouldn't do what I want to do and need a unit that is AC Powered.

Shure attenuator is on catalog of fullcompass and number is A15AS on p. 284 I think the person I was talking to is wrong. What would happen if I didn't put though attenuator?
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Old November 14th, 2002, 06:09 PM   #2
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I don't know what a KM201 microphone is so I don't know what you need. Does the microphone put out millivolts (microphone levels or line level?

You are going to plug into a minidisk. Mine has separate line and microphone inputs so the major level changes are handled there. Then my MD has a level control which so far, has managed to handle everything I throw at it.

The phantom supply doesnt' enter into the picture, signalwise.

Guess I don't know why you would need one unless you are sending line levels to a microphone input. I used to do that and I bought the Shure fixed attenuator. I think it has around 50 db of attenuation. Shure also has a switchable attenuator too. Still don't know, with the information you've provided, why you would need one.

I also don't know why a powered attenuator (strange as that sounds) would be necessary.
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Old November 14th, 2002, 07:01 PM   #3
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Recording a show with a pair of KM201 which looks like:

http://www.sound-room.com/mofcart/elation.html

I don't know if the microphone put out mic level or line level... When I used AT822 with minidisk, AT822 doesn't seem to put out line level. I had to plug the microphone to mic-in instead of line-in.

right now this is the last question I need to get answered. Sorry for filling up boad with unrelated question.
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Old November 15th, 2002, 05:55 PM   #4
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OK. These mirophones output at microphone levels, not line levels. So why did the salesperson try to sell you an AC-powered attenuator? Who knows.

There are microphones out there (The Sennheiser MKE150 comes to mind) that have such a high output that an external attenuator isn't a bad idea. Without being able to test the microphones beforehand, if I were short of time, I'd probably spring for the adjustable Shure attenuator and place it before the Phantom power module.

Something like a Beachtek or Studio 1 XLR to minijack box would also work. And give you a finer control of output levels than the Shure which switches in attenuation 10 dB at a time IIRC.
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Old November 16th, 2002, 08:06 AM   #5
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I was testing my Elation KM201 and it's doing something strange. I connected the microphone then connected the cable to Deneke phantom power supply, then to minidisk. When I turned on my MD, I heard this noise that goes like, "SHHHHHHH.... pop! pop!" I made a sample mp3 of it because I can't descirbe it well.

It's 860kilobytes mp3:
http://207.44.160.90/~admin7/staticnoise.mp3


1st one is the matched pair of Elation KM201s and 2nd one in the sound bite is T.H.E KA-04 with KR2c cardio capsel. The 2nd microphone doesn't make noise.

I don't know why Elation mic is making such a loud noise. I think I broke microphone. It is bought a 2nd hand one, and has 8 hours use on it.

This is how I connected:

Mic->Ramtech XRL cable->Denecke Portable Phantom power->XLR
Mic->Ramtech XRL cable->Denecke Portable Phantom power->XLR
then those dual XLR goes to stereo mini.

Does this have something to do with connecting Balanced out to unbalanced input. Person who sold me Denecke Phantom power supply (DEN-PS2) said that what comes out of the power supply is unbalanced. I connected Elation KM201 to my PD150 directly and I didn't hear any strange static noise.
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Old November 17th, 2002, 12:08 AM   #6
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Couple of possibilities here.

One is the mini-jack adapter is not wired correctly. I think this is unlikely. You should check it in any case. But you say the 150 records the sound OK. That makes me think that the microphone power coming out of the MD is causing the microphones to do something strange.

When you fed the signal into the 150, did you use the on-board phantom power or did you use the Deneke to power the microphones? If you used the Deneke, then you know it works in a 'regular' environment and you need to look at the circuits beyond the output of the Phantom supply.

If you look through Jay Rose's past columns on the DVMag web site, you will find an article in which he describes the insertion of a voltage blocking capacitor in series with the signal line of a microphone to avoid a buzz that is caused by the DC power coming out of amateur recording devices. He was writing about camcorders but the MD is in the same situation, I'd guess.

The capacitor is small and can be hidden inside the XLR shell. You would need to add two capacitors for a stereo system.

Were the microphone broken, it would not work with the 150.
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Old November 17th, 2002, 12:26 AM   #7
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Dear Mike,

Jay said that maybe the Deneke power supply is causing the whole connection to be unbalanced (if the seles rep I talked to was correct. He said Deneke SP2 phantom power supply would output unbalanced signal. Jay says this is unlikely).

The strange thing is though, that the pair of T.H.E. KRC2 microphone which is also professional grade mic which use XLR output did not make any static noise at all. it is the second sound bites that's on the mp3 I posted and it seems to be able to capture sound well, compaired to Elation KM201 (I had to crank up recording level to 29/30 to get that mp3 recording posted) which is also strange.

When I used PD150, I used onboard power supply only.

I'm going to test

1) Use Deneke in conjuctnion with PD150
2) Use Clown phantom power supply with Elation KM201s
3) Read Jay's article about consumer device putting out DC volatge.

Thank you mike, and I'll report it back !
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