Zramo 'BM-700' with much better capsule

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k brown

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These BM-700 style mics being sold on Amazon show a completely different capsule than the usual TSB-160a (or copy thereof). It's no hype - I bought a pair and the larger capsules are not just much better, but with cleaned-up electronics, and the top end cut back a bit on the mixer, they compare VERY favorably with my Oktava 319 and AT3035.

These capsules bear a passing resemblance to the TSB-2555, but have a narrower front rim and a different hole pattern on the back. The exposed diaphragm area is about the same as the 3035. To check the noise of the capsule itself, I hooked it up to a 2SK660 and known quiet biasing circuit, and they are very quiet.

Since the capsule has a built-in fine mesh, I removed the inner mesh from the front half of the head basket; no noticeable hum. By plugging one of the rear vent holes, the sound at 180 degrees was less 'scooped'.

Someone is selling on e-bay capsules that appear to be the same; I haven't received it yet so can't confirm if it is.
 

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k brown

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Here's their listing for the capsule alone; for $3 more you get the body, and a pretty good shock mount!
 

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k brown

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Looks identical - wow, four bucks !!

What's weird about that listing is, that's clearly the same capsule and it's not aluminum - the housing is clearly solid brass; I just did a 'scratch test'.
 
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homero.leal

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CM012 is only Zramo's part number, but they are not the manufacturer of the capsule.

I still haven't found who the original manufacturer is.

Regards.
 

k brown

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That's what I figured.

I'm surprised how well these work as omnis, with the rear vents plugged up (as reported earlier by kingkorg). Also as sub cards with all but 3 or 4 closed. They must be tensioned somewhere between the optimum for cardioid and the optimum for omni. The oft-heard claim that diaphragms must be tensioned differently for the two patterns always puzzled me a bit - were that the case how could the Sony C37a sound so good, or the switchable Schoeps capsule, which Marc Aubort used his entire career?
 

kingkorg

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The oft-heard claim that diaphragms must be tensioned differently for the two patterns
It's a myth, don't waste your time on tension. Tension is a part of the equation, there might be other reasons why some capsule uses higher tension. Sometimes it's just a production variation.

As a rule of thumb with higher tension you get lower output, more extended HF FR, and less low end. Also less plosives and posibility to polarize the capsule with higher voltage. But there are so many other parameters that affect the same.

Since you are into orchestra recording, give something like this a try, worked great for me. With closed holes on the back off course.
 

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k brown

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Indeed, I have. I've made 40mm and 50mm APEs for my MC012s and my beloved little Primo EM50s; in both clear acrylic and hardwood. I'll be making them for these caps too. You should try smaller balls - anything larger than 50mm is going to give you a pretty 'pushy' upper midrange.

Regarding the rear vents, a very famous classical engineer that asked to remain anonymous on this point, suggested blocking half the vents on cards to create subcardioids.
 
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