mic pre - a tiny line-level electret microphone preamp for Norns/modular/field recording and whatnot

Durdee · 2022-08-10T14:57:28.072Z

Just burned out my first tiny board. I have yet to pull it back apart to see what went wrong, but the end of the mic tube got a bit warm and then that was that. Battery died. Hmm……

kasselvania · 2022-08-10T16:08:52.051Z

I got some Kapton tape for when I revisit the build to keep the battery wires/contact points away from the tubing. That seems to be the most likely point of contact and shorting

forrest · 2022-08-12T19:49:06.200Z

Love this project so much but I needed something stereo for my Clippy EM272 stereo pair so I designed a stereo version using the reference design you provided but changed all the values to work just right for the EM272Z1 capsule. Using some cheap extruded aluminum boxes and printed pcb’s as ends. The sound is so clear, so much better than when I have used them through some cheap field recorders in the past. I added the ability to bring in dual mono and input dual mono as well.

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ramphands · 2022-08-13T02:58:15.634Z

Lovely recording!
Wow those EM272s are specced extremely well. -28dB sensitivity at 80dB S/N.

What values did you use to suit the capsules? I may have to try some for myself if I can get the capsules. Seems like Primo, while being a Japanese company, don’t actually sell their capsules in Japan, only finished products.

kasselvania · 2022-08-13T04:55:47.036Z

I’m in the states and had to purchase some European ones. Odd.

forrest · 2022-08-13T10:28:38.863Z

Thanks!

I’ve put everything in a github repo so you’re welcome to it. Lom’s Uši Pro uses the same capsule, so this design should work for them as well.

As an aside, this box seems to work OK running my LOM Elektrouši (I don’t think these are supposed to use plug-in-power) Here is a recording of my 128 grid (the device itself) running ‘Awake’ through these stereo electromagnetic mics (with 10k+ rolled off, there was some high frequency noise)

PedalsandChill · 2022-08-14T16:28:58.808Z

I’m sorry to bug ya again. But, I seem to be finding a heck of a time finding the file that details the placement of all the parts. Could you fill me in on what I’m overlooking?

ramphands · 2022-08-14T16:33:28.766Z

Hello! No problem at all.
For each version of the board, in the BOM folder there should be an HTML file called “ibom.html” - that will bring up an offline webpage which has all the components and their locations. Hope that helps!

PedalsandChill · 2022-08-14T16:34:25.289Z

That was it!
Thanks for the help and quick response!

::edit::
@kasselvania Which part did you buy that was incorrect?
I believe I may have done the same thing. I got it all soldered and put together last night, powered it up, but the volume is incredibly soft.

kasselvania · 2022-08-24T14:18:01.031Z

I incorrectly purchased this amp:

OPA172IDBVT

While I should’ve (and eventually did) purchased this:

OPA172IDCKR

The way that I could tell that they were incorrect was that the first one was actually too big for the footprint for the IC on the PCB.

Even after having the correct part, The mic didn’t initially work! I had to reflow all the contact points and found a faulty one. The tiny mic pre is TINY and is a bit tough to build, even though there are very few components.

ramphands · 2022-08-24T17:01:14.293Z

Yeah the tiny version isn’t the friendliest thing ever.

The regular version is tricky enough for people who don’t have experience with SMD - it requires a bit of thought about the order you place components so as not to make it really hard to get your iron in to solder the last components. The tiny version is even less forgiving, however.

kasselvania · 2022-08-24T17:29:37.644Z

To add to this, I suggest anybody building the tiny mic pre, GET KAPTON TAPE!

It’ll help give security so that the wire joints don’t happen to touch the aluminum tube and cause a short!

PedalsandChill · 2022-09-15T23:22:36.468Z

Hello! I looked over your schematic, I think I have all the right components. Any chance you’d be able/willing to look it over and tell me if it’s correct before I place the order?
::Edit::
Forgot the link.
https://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=e26bbc3bf6

ramphands · 2022-09-16T03:52:48.860Z

Is this for the tiny version?

I see you’re missing the electret microphone and also some of the parts are the wrong size.

There’s a cart linked on the Github page with the right bits:
https://www.mouser.jp/ProjectManager/ProjectDetail.aspx?AccessID=1ea3a70ac9

Hope that helps!

By the way, the opamps are on backorder from Mouser but can be sourced from LCSC and perhaps some other places.

PedalsandChill · 2022-09-16T04:27:47.804Z

Actually, I put together one of each of your layouts. I was blown away by the clarity of that electret mic! But I meant @forrest layout. Yours were such fun builds, I thought I’d take a crack at their build too! Accidentally dropped a couple op amps in the process though.

forrest · 2022-09-16T10:28:35.827Z

I actually sourced everything from lcsc and had jlcpcb assemble the boards for me, its so inexpensive these days and saves some hassle, pretty sure the stencil layers are in that gerber so ya can probably just upload the bom during that process.

Edit: oh it looks like I didn’t upload the placement csv, thats on another computer, i’ll upload it in a day or two then you can just have them build it, easy peasy.

Edit 2: updated the repo with the placement csv

ramphands · 2022-11-27T07:34:42.155Z

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Finally built up the tiny version. Have to get some suitable wire to finish them off. I’ll be interested to see if there’s any noticeable audio difference between this version and the original. In theory, due to the shorter distance between the mic and the circuitry, it should be less prone to interference, although I didn’t really notice any with the original.

Rodrigo · 2023-01-22T18:42:03.363Z

I got to thinking about a project where I have a mic mounted to each finger in a glove for really dense explorations of the mic/friction stuff (like this) and I remembered this project. Specifically the Tiny Mic Pre variant.

I could conceivably have 4 (or 5) of them on little finger mounts (banjo/finger picks?) and have all of that going to a breakout box with a battery (presumably you can power all of them off a single battery?), then have that go onto the rest of the system from there.

Does anyone have spare PCBs for this in the UK/EU?

monopole · 2023-01-22T19:02:29.205Z

@Rodrigo I have a few spare stereo preamps designed by @forrest up here, based on the same design.

Rodrigo · 2023-01-23T01:04:24.530Z

Hmm, that does look good, but those mics are definitely on the big side, though it would be interesting to consider just having the capsules themselves on their own, and having whatever else in a breakout box handling the power. I guess you risk more noise, but given what I’m doing, that’s not a huge deal.

Lemme have a think on it and I’ll drop you a PM if it seems like it would work well (wouldn’t want them just sitting here unused if it’s not).