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Old 8th March 2009, 05:33 AM   #1
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Default wm-61 measuring mic

I know these mics have been discussed for a bit before. However I was just thinking since we always measure through a laptop or computer nowadays, would it not make sense to draw power through usb? I presume usb +5VDC is pretty clean? would I get any problems if I used the usb +5VDC instead of using a 9V battery? The datasheets point out a nominal voltage of 2V to a max of 10.

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Old 8th March 2009, 01:29 PM   #2
infinia is offline infinia  United States
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Yes
preamp+ADC at USB will be used as well to make it practical.
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Old 8th March 2009, 08:26 PM   #3
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I was hoping the built in preamp in my m-audio transit would be enough.. I don't feel like building a preamp.. mine have all failed =(. I was just going to do a 3.5mm plug and usb hybrid that will terminate in a female 3.5mm plug which is "powered" so the mic will get power..
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Old 8th March 2009, 09:18 PM   #4
Ron E is offline Ron E  United States
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Well, you can just use the mic input on your sound card. That provides a 5V bias automatically. You wire the + on the mic to the tip and ring and wire the - to the sleeve, IIRC.
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Old 8th March 2009, 09:59 PM   #5
Dr_EM is offline Dr_EM  United Kingdom
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Yes, the mic input on a computer supplies a 5v bias specifically for electret capsules (as are commonly used in PC mics).

However, regardless of how you power your mic capsule I'd strongly reccomend a good quality pre-amp to go with it. The pre-amp inbuilt on computers is usually of very poor quality, they have a lot of noise and likely distortion too; not ideal for measuring. A good quality pre-amp can be built very simply and a kit like below will make it very easy. You can then hook up to the line input which bypasses the low quality pre-amp:

http://www.madaboutsound.com/prod_de...1&sa=cf&ctid=4

I am not certain if this kit could be powered by 5v but somebody can hopefully confirm
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Old 9th March 2009, 06:47 PM   #6
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well I was using my external soundcard, it is definetly better than my internal sound card, I don't have a line in anywhere so I'm out of that option, maybe I can just plug it in and see how it sounds.. can I measure the 5V by plugging in an interconnect and taking a volt meter to it?
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Old 9th March 2009, 07:00 PM   #7
infinia is offline infinia  United States
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Yes you can ...mic input is a 3 wire with a gnd, pre-in, and Vs.
What's wrong with Linkwitz preamp and capsule mods ?
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Old 9th March 2009, 07:11 PM   #8
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I am using the linkwitz mod, but wasn't planning on the preamp.
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Old 9th March 2009, 07:54 PM   #9
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Try these threads:

Few questions about Linkwitz' mic amp circuit
http://forums.anandtech.com/messagev...&enterthread=y
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Old 9th March 2009, 10:06 PM   #10
infinia is offline infinia  United States
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Plan on a pre-amp esp if doing the capsule mod. The gain (mic fet) is cut to less than 1 for lower noise and higher spl.
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