Hidden mini omni gem.

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k brown

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I know there's not a whole lot of interest 'round these parts in SDC omnis (this is kind of a multi-pattern LDC playground), but I thought I'd share my discovery of these beautifully-made mini capsules from inside an Audio Technica AT841R boundary mic.

Separated from their stock power modules with tiny tunes transformers, and hooked up to a quality transformerless circuit, these sound amazingly good; and shockingly quiet for such a teeny thing: 7.5mm outside diameter, with a built-in 2SK660 FET (and NOT SMD) and RF caps. With the top tamed about 3dB, these hold up extremely well against my Sound Room cherry-picked Oktava MC012 omnis.

The later iteration of these (in the U841R) have just a simple, small hole in front of the diaphragm, instead of these precision-machined slots. Body is not stamped aluminum, but machined brass. The actual capsule unscrews from the tiny back-end that holds the little PCB with the FET on it.

Though the published response curves are quite similar, they sound way less bright than my Shure Microflex omnis (which I've never been able to find a use for, except inside really dull pianos).

The top end is less hot hooked up to an 8533 power module, compared to it's stock module; maybe a boost circuit in it?
 

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cyrano

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I use several AT lavaliers and love them for outdoors use. Same 8533 modules. Balanced cable for a non-balanced connection. Some of these are "hanging" choir mics and come with 9 meters unbalanced cable between electret and power module.
 

k brown

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Here's the first complete build with these little beauties. Tucked into the back-end of a TA3F connector, using it's strain relief to secure the cable.

For power modules, I'm using the boards from AT8533 modules, with the transformers replaced by impedance-balanced outs and phantom-feed resistors.

Still amazed how quiet these things are for their size. At least half the noise was from the stock power modules, which appeared to be very much like the 8531 modules, but with SMD parts and some different values. 8533 is a more sophisticated biasing circuit.
 

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cyrano

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Nice.

Mine are AT853 with 8533 in the XLR. I used four of them for my first ambisonic experiments. And some others. I like the entire range, cause they're small and you can still order anything in parts from AT. Even for stuff that's over 20 years old.
 

k brown

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Second build with these little guys - much more robust, and look much less silly up on a stand! Also allows mic clip/shock mount to be placed further from capsule.

Carbon fibre tube in heavy duty 1/4" plug barrel.
 

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