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.
Thanks!
Thanks!
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_det.asp?cid=111&sa=cf&ctid=4
I am not certain if this kit could be powered by 5v but somebody can hopefully confirm
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_det.asp?cid=111&sa=cf&ctid=4
I am not certain if this kit could be powered by 5v but somebody can hopefully confirm
hm. I've got 2 opa134-pa on hand. would those work for the preamp?
sigh. i dont want to buy anymore components, shipping burns..
I was going to use this schematic. http://www.linkwitzlab.com/images/graphics/microph2.gif
sigh. i dont want to buy anymore components, shipping burns..
I was going to use this schematic. http://www.linkwitzlab.com/images/graphics/microph2.gif
haha. like I said. I'm hoping to make do with as few parts as possible. 1 9V would be nice, I tried basing it off a cumoy amp and somehow my biased power supply totally fried one of them, so hot it burned off a couple layers of skin off my fingers. actually its not too much for speaker testing as i need it for real time spectrum analysis for live sound reproduction.
are you referring to this one?
http://www.linkwitzlab.com/images/photos/mic-amp.jpg
so i have to double it up eh? I need to find a supplier here ..
http://www.linkwitzlab.com/images/photos/mic-amp.jpg
so i have to double it up eh? I need to find a supplier here ..
nukaidee said:
Then you might use a switched gain for adjusting the preamp gain (higher) to find the sweet spot after your setup is finalized.
If your post/preamp cable runs get too long >50-80 ft then this might not be your best solution (noise EMI pickup).
Just use two 9V batteries as the above post.
nukaidee said:
That's the one. Can't find a 2.2uF cap? - drop in a 1 uF, because - unless you have access to an anechoic chamber or are measuring outdoors in a field - you don't need an F3 of 7Hz. All of the other values can be found in any town with an electrical supply company. I think you mentioned having the OPA 134, so you can skip the unused second IC in the schematic.
I think he should be able to do it with only one 9V battery. He'd need a rail splitter, but I used one for mine even though I had two batteries.
You can find plenty of 2.2 uF electrolytics which should be better than tantalums in this app.
I'm busy right now, so I can't attach the whole thing, but if you are not too worried about noise you can do this:
order TLE2426CLP (3-pin package) sample from TI
1x 9V battery clip from digikey or local
1x ~100uF electrolytic cap
1x SPDT toggle instead of DPDT
1x patterned perfboard (Radio Shack 276-0150 works very well)
That basically takes care of everything that isn't shown on the schematic except for the enclosure
You can find plenty of 2.2 uF electrolytics which should be better than tantalums in this app.
I'm busy right now, so I can't attach the whole thing, but if you are not too worried about noise you can do this:
order TLE2426CLP (3-pin package) sample from TI
1x 9V battery clip from digikey or local
1x ~100uF electrolytic cap
1x SPDT toggle instead of DPDT
1x patterned perfboard (Radio Shack 276-0150 works very well)
That basically takes care of everything that isn't shown on the schematic except for the enclosure
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