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Author Topic: CA 9100 with BM-700?  (Read 782 times)

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Offline SquirrelMurphy

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CA 9100 with BM-700?
« on: January 15, 2020, 06:32:16 PM »
Hi all. I've been wanting to try one of those Pimped Alice mods on a Chinese BM-700 or BM-800. You can get the mic for $5-$20 and mod it for $10-$30 so it'd be a fun build to try. Search on eBay or Ali Express (or even Amazon) for BM-700 and BM-800 and you'll see what I'm referring to.

One of these guys (if it's not showing, this link)

These are fairly large condenser cardioid studio mics and I think pretty much one company supplies them for branding and resell by dozens of other Chinese companies. The mod is a replacement condenser and replacement circuit. You use the mic as a donor body essentially.

From what I've read, the BM-700 typically ships with an XLR to 3.5mm cable and needs at least 3V-5V to run. People use it on their PCs for podcasting or whatever. No pre-amp required, but it's recommended. I think it's meant to look like a U87 clone. There's also a BM-800 is similar but requires 48V phantom power so I'd run it through a mic pre-amp.

My question: I have a CA 9100 that I run CA-14 cards through for field recording. It supplies 9V and has a 3.5mm stereo interface which matches what they commonly ship with the BM-700. That'll work OK, won't it? It's a mono mic, so I presume I'd get left-channel only.

I like the BM-800 design better, but the requirement for 48V phantom power means the 9100 is off the table, connector would be XLR<>XLR and it'd probably never leave the house. But the BM-700 could potentially be used in the field like my CA-14s if I could use the existing pre-amp. Maybe heavy battery suckage?

Also thinking a bit about building two for stereo recording... could be interesting.

Cheers and thanks...

Offline heathen

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Re: CA 9100 with BM-700?
« Reply #1 on: January 16, 2020, 09:39:28 AM »
You should try emailing Church Audio directly with this question.  I've found him to be pretty responsive to emails.
Recordings on LMA:
Mics: AT4050ST | AT4031 | AT853 (C/SC) | Line Audio CM3 | Sennheiser e614 | Sennheiser MKE2 | DPA 4061 | CA-14 omni Pres: CA9200 | DPA d:vice Decks: Zoom F8 | Roland R-05

Offline kuba e

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Re: CA 9100 with BM-700?
« Reply #2 on: January 16, 2020, 10:38:04 AM »
If a microphone can accept 9V power from CA9100 and has an unbalanced output then it should be possible. Edit: I am not sure about the next, probably following strikethrough is wrong and it is not needed You have to change TS jack to TRS otherwise you will create a short circuit in CA9100. Let the ring unconnected in TRS jack. Or connect the second microphone there. The last thing is microphone's output impedance. CA9100 has input impedance 10k ohm. So probably mic with output impedance around 1k ohm or less is ok.

But I am not specialist. The best is to ask Chris as Heaten advices.
« Last Edit: January 16, 2020, 10:50:41 AM by kuba e »

Offline SquirrelMurphy

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Re: CA 9100 with BM-700?
« Reply #3 on: January 16, 2020, 01:20:54 PM »
Yah, OK... thank you both. I'll ping Chris. The things you mention -- like TRS pin-outs -- I would not have considered (a bit of a noob). He'll probably want specs for the target mic. Specs vary from one brand to another, but for what it's worth they are generally:

Sensitivity: -38dB±3dB
Working voltage: DC1.5 V-10V. People report that it works fine at 5V.
3mA current
FR: 20 - 20K or sometimes 30 to 18K
100-150 Ohm output impedance (1K-Ohm load, sometimes 2.2KOhm_
Max SPL: 130dB
Noise level: 16.0 dB(A)
S/N Ratio 78dB

Might be safest to just just start with the BM-800, XLR, +straight-up phantom power from a pre-amp (I have one) and play around with that before messing with portable. I'll learn a lot during the process of building the circuit board -- and that's what this is all aboot.


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