How to build a Stereo Microphone and Battery Box

[Malcolm Stewart]

Many thanks to Greenmachine for publishing the details of his battery box. I went shopping last Monday and spent a happy time putting it all together. I used a mini plastic case from Maplins and it's a good fit. (Order code JX56L and it comes with a cable relief grommet. I bought a pair of cheap earphones so as to obtain a lead with a gold plated stereo plug. In the past I've found this helps keep noise down - particularly where power is supplied along mike leads.)

Then came the big test, and things weren't so good. Instead of the monitored sound being similar to what the plug-in power Mic socket on my NH900 provided, it was heavily distorted. So I tried again last night capturing quieter(?) birdsong in the garden, definitely better and then after about a minute, the monitored sound cut out all together.

Panic.

Had I blown my NH900?

Fortunately, the answer lay elsewhere. As I'm somewhat deaf I use a Soundprofessionals Headbanger amplifier between my NH900 and my 'phones, and the (rechargeable) 9V battery in the amplifier had chosen the time of this most important test for its voltage to dip below that at which the Headbanger works cleanly. Recharging for a short period and I was listening to good sound - phew... I'll have to add a battery voltage zener in my (modified) Headbanger's LED "ON" circuit to ensure that I get warning when the volts drop below 7V or so.

[tangerine]

Hi all,

I have some questions about this device.

Can I use tantalic capacitors instead of the electrolyt ones?

Will this work with any recording gadget? (I don't own a MD recorder, I have an Archos Gmini 400).

Is it possible to measure the line-in impedance?

thx

[pepsi_max2k]

weyhey, another gmini 400 owner

anyway, i just found out i can attach a 9v battery (after a bit of soldering, just found a cheap soldering gun but i'm still minus a hot glue thingy) to the cheap battery box i already have, so i'm gonna try that first. if it don't work - malcomb, i guess you're from the uk. did you get everything you needed from maplins? i might have to make a stop off there on my way back from uni how much did it all cost you?

Edited May 20, 2006 by pepsi_max2k

[Malcolm Stewart]

malcomb, i guess you're from the uk. did you get everything you needed from maplins? i might have to make a stop off there on my way back from uni how much did it all cost you?

Using the small plastic box, I didn't need to use hotmelt glue (which I don't have). I bought everything from Maplins in Milton Keynes. The most expensive item was the cheap earphones (from which I removed the lead and gold plated stereo plug) at £4.99. Other items including the PP3 battery clip, stereo socket & case cost about £3. I used a small piece of copper strip board to help neaten my wiring, and I drilled and screwed the 9V battery connector to one side of the case. I was surprised at how long I spent cogitating before cutting plastic! (Nobody would make a profit employing me these days.)

To Tangerine

I can't think of any reason why tantalum capacitors can't be used instead of aluminium electrolytics (they're a similar size), but it's not my field and others may advise differently.

Testing, or not testing the box

I still haven't found sufficiently loud sounds (not from loudspeakers) with which to try out my battery box and microphones. This pm I tried recording the noise underneath a metal girder bridge, on the West Coast Mainline, when a Pendolino was thundering above me. Very much quieter than I had expected and much of the (expected) noise had been dampened by a concrete infilling to the underside of the bridge! Certainly the meters got nowhere near -12dB when using the Line Input.

I had hoped that this fairly repeatable noise would allow me to tell the difference between various modes such as Mic In, Line In, AGC modes etc.

[tangerine]

Thx for the answers.

I will use the tantalic (or tantalum?) capacitors.

to pepsi_max: I'm from Hungary. Everything was cheap except for the mics they were 1100 HUF (~4 €) each.

I bought some 3.5 mm stereo sockets but they are too bulky (chinese rubbish) to build in. So I decided to get them from some old CD-ROM drives (headphone output). That is much smaller and better quality.

Edited May 21, 2006 by tangerine

[tangerine]

I've made two of them.

Battery box #1

Battery box #2

[Malcolm Stewart]

I've made two of them.

Battery box #1

Battery box #2

Looks good to me, and some pretty good close-up photography as well!

[tangerine]

Looks good to me, and some pretty good close-up photography as well!

Thx.

Photos are resised to 33% of the original.

[pepsi_max2k]

woohoo. got my stuff from maplin, i'll put up the catalogue numbers later for anyone else in the uk, just gotta confirm they work first which brings me to my next problem...

for the sake of anyone else who last did anything with circuits 5 years ago in high school, could someone clarify/fix the following for me? i know it's wrong, there's at least the middle part of the jack wire (in this pic) going no where at the moment, and between me not understanding the diagram, not being able to see where the wires are going in the photos, and having a stereo socket with 3 wires instead of 4 like in the original, i've no idea what i solder to what. so err... if anyone would be kind enough to join the dots in the pic, please repost the correct version. thankyou

ps. remember, it's a drawing of wires for noobs to understand, not a circuit diagram, so no fancy stuff / laughing at the idiot

edit: probably need someone to tell me what's what on the socket too the pin at the front is connected to the round bit at the front, the pin on the right in the first pic has a kinda flat bit lying along the edge, and the left one has a curved bit coming down opposite the flat bit.

update: just added what i think is l/r/g after looking at which parts of a jack plug the bits touch.

EDIT 2: had another look/think about it, came up with this:

which is based on the assumtion of this: (g was for ground, though I've no idea what it actually is...)

any better?

Edited June 10, 2006 by pepsi_max2k

[cribble]

Ello, First time poster here.

Was very inspired by this to make my own mic's and hopped on the train.

My first attempt was crap - i used the mic's from Maplin with the crap responce freq (50hz-13khz), i used to stiff of a cable to make it flexible to put it into any position and the sound distorts at the sound of cymbals - must've been a freq range thingy. They look like this...

i used black tape, because i decided to do everything on the cheap.

Then i found a website that supplied 20-20khz mic's and was all over it in no time. So i ordered a batch and install some into headphones:

These still need to be sanded a little as the plastic is abit rough around the mics. Other than than, you goto a gig and no one ever knows. These babys are awesome. Here's a band rehearsal i recorded [link] - i've only boosted the volume - no eq's, compressors etc were added.

I have a question about the batterybox. I want to add some bass roll-off's to it, anyone know how?

Edited June 10, 2006 by cribble

[tangerine]

[looonie]

being a total noob on electronics, i've to ask if i can just get a stereo to 2 RCA cable and cut off the ends of the RCA sides then solder on the mics?

[pepsi_max2k]

cheers tange, basically got it on my second drawing but with the red/white stereo wires the wrong way round

[pepsi_max2k]

hmm well. just made it. only getting sound through the right ear, which appears to be coming from both the left and right sides of the mic. and a high pitched sqeak through the left ear, changing from the left to right ear when i wiggle one of the capacitors. but i guess i'm halfway there

on the other hand, i just attached a 9v battery connector to my old 1.5v battery box and it works fine, though can't hear too much of an improvement with it.

Edited June 11, 2006 by pepsi_max2k

[Malcolm Stewart]

hmm well. just made it. only getting sound through the right ear, which appears to be coming from both the left and right sides of the mic. and a high pitched sqeak through the left ear, changing from the left to right ear when i wiggle one of the capacitors. but i guess i'm halfway there

on the other hand, i just attached a 9v battery connector to my old 1.5v battery box and it works fine, though can't hear too much of an improvement with it.

The joys of miniature(?) electronics!

Sounds pretty familiar to me when trying to make gear as small as possible; and without the expensive and specialised tools our technicians had at work. I'm sure you'll get it corrected quite quickly.

I wouldn't expect any improvement when using the 9V battery unless you're recording very loud sounds which would cause pre-amp clipping with the inbuilt pre-amp. (There might be a small improvement in noise level if the electrets are optimised for 9V usage, but I'd expect you'd need a meter to measure that.)

[mudihan]

Omitting the capacitors?

I will be using M-audio Transit USB DAC/ADC to record concerts on my laptop. I think the unit does have input capacitors behind its mic-in/line-in. If that's the case, do I still need 2.2uf capacitors? I do prefer a purer signal path. Thanks!

[cribble]

Does anyone know how to install some bass roll off to the battery box?

[greenmachine]

Basically, if you want bass roll-off, you need lower capacity capacitors (something in the 0.xx uF range). See here: >>click me<<

I'd recommend to capture the full spectrum instead and filter afterwards via software if necessary though.

Omitting the capacitors?

I will be using M-audio Transit USB DAC/ADC to record concerts on my laptop. I think the unit does have input capacitors behind its mic-in/line-in. If that's the case, do I still need 2.2uf capacitors? I do prefer a purer signal path. Thanks!

Without being certain about the existence of input capacitors, i wouldn't risk it.

Edited July 2, 2006 by greenmachine

[cribble]

Cool, and thanks for the link, one more question just before i mod my battery box: is it really worth having the bass roll-offs?

Because i hear you can just eq out the bass later. People keep telling me it will stop bass distortion, but thats the mic's fault, not the players/recorders fault, right?

[greenmachine]

The capacitors (bass rolloff filter) sit behind the mic's output (between mic and recorder's input) and thus don't have an effect on the SPL handling of the mics. If your recorder has only a mic-input (no line-in, like many camcorders, but unlike MD recorders), the lowered output in the lower frequency region can lower distortion of the recording in high SPLs by less overloading the preamp.

Virtually all MD recorders are equipped with a line-in though, which cannot be overloaded easily even at very high SPLs (unless you have extremely sensitive mics). Thus no bass roll-off will be necessary if you record via line-in. Correction via software is more precise than a fixed 6dB/oct filter anyway.

Be sure to always keep an unedited master.

[lalomania]

Just built my battery box, it sounds great! Thanx greenmachine. One question.

Can i use any tipe of glue for the casing?

[greenmachine]

Hot melt glue will work best - dries fast, is inexpensive and non-toxic, will make a solid housing.

[pepsi_max2k]

just replaced both capacitors and both resitors on the thing and it still insists on only outputting sound from the left ear i give up, at least the old one i bought with a mic works ok

[greenmachine]

I wish i could help, but it's hard to find the bug without at least seeing your construction. Any pics?

[pepsi_max2k]

I wish i could help, but it's hard to find the bug without at least seeing your construction. Any pics?

sorry, i would've added them to the previous post but it's currently 30 miles away i'm sure it's soldered together exactly how it should be, and there's little i can see that could be wrong with it other than maybe a connection on the stereo socket. i forgot to mention i even changed the stereo lead and it didn't affect anything. i'll try post some pics when i can

[lalomania]

Hot melt glue will work best - dries fast, is inexpensive and non-toxic, will make a solid housing.

Ok, but suppose i cant get any hot melt glue, could i use any glue that i find in my house?

Edited July 9, 2006 by lalomania

[tangerine]

I've made my first recording but not too happy with the result.

Can it be improved somehow?

Does anybody know how to do it with Sound Forge?

I used a pair of modified (lowered sensitivity) mics (MCE-2000). (Post #18)

The rec gain was set to 14 (out of 15) on my Gmini400

Here are some untouched samples (3 x 1 min, ~5 MB each)

sample 1

sample 2

sample 3

(edit)

Another sample (whole song ~ 26 MB)

Electronic Apeman

Edited July 9, 2006 by tangerine

[greenmachine]

The download is very slow /doesn't work, but have you thought about mic placement, how do you do it? Also you cannot expect great results when recording from a stack of speakers or any other low fidelity source.

[tangerine]

The download is very slow /doesn't work, but have you thought about mic placement, how do you do it? Also you cannot expect great results when recording from a stack of speakers or any other low fidelity source.

Sorry for the slow DL (no problem here) I'll try to UL somewhere else. (any idea where to?)

Here is the position of the mics (and me).

Edited July 10, 2006 by tangerine

[greenmachine]

You can use the gallery of this forum for uploading samples. Flac files are rather huge though and should only be used when perfect accuracy is necessary. Otherwise well encoded mp3's will do. I'd suggest to create a new thread to discuss the subject in depth.

[lalomania]

sorry i keep insisting, but can i use any glue that i find in my house, im sorry but i just cant use hot melt glue.

[The Low Volta]

hot melt glue becomes liquid when heated (by the glue gun) and it dries really solid when it cools down again. Other glue types do not really show the same behaviour (they often do not dry out completely which leaves a mess or could even ruin other parts when inserted like your mic stereo-plug)... I wouldn't trust any other material personally, but if you really really really can't find hot melt glue (available in any decent DIY-store and you could always send someone to pick some up if you aren't mobile at the moment) I still would advise you to try the material you wanna use on something dispensible (but as much like he real battery-box as possible) first (and give it enough time to dry and test it rigorously before applying for real)

it seems no-one here has found himself in the situation where they neede hot melt glue but culdn't get any, so I'm afraid no-one will be able to give you a definite answer... it's guineepig time

[lalomania]

hot melt glue becomes liquid when heated (by the glue gun) and it dries really solid when it cools down again. Other glue types do not really show the same behaviour (they often do not dry out completely which leaves a mess or could even ruin other parts when inserted like your mic stereo-plug)... I wouldn't trust any other material personally, but if you really really really can't find hot melt glue (available in any decent DIY-store and you could always send someone to pick some up if you aren't mobile at the moment) I still would advise you to try the material you wanna use on something dispensible (but as much like he real battery-box as possible) first (and give it enough time to dry and test it rigorously before applying for real)

it seems no-one here has found himself in the situation where they neede hot melt glue but culdn't get any, so I'm afraid no-one will be able to give you a definite answer... it's guineepig time

Thanks, i'll have to take my chances. I'll post the results...

The real reason why i couldnt get any hot melt glue is economical, it just seemed a waste of time/money to buy a hot mel glue gun, and a "cartridge" for it just to use a little bit on my Battery Box. Although I'm having second thoughts about it, how much does a hot melt gun plus the "cartridge" for it cost?

[greenmachine]

I've seen low cost variants for as low as 1€ per gun including 2 sticks and 1€ per 12 pack glue sticks. Quality equipment isn't too expensive either. You'll propably need no more than one glue stick for a miniature battery box. It's a great tool for any kind of DIY though.

[lalomania]

I've seen low cost variants for as low as 1€ per gun including 2 sticks and 1€ per 12 pack glue sticks. Quality equipment isn't too expensive either. You'll propably need no more than one glue stick for a miniature battery box. It's a great tool for any kind of DIY though.

I thought it was really expensive, nice to know its cheap.

Anyways I couldnt wait, so i tryied using a regular "school" glue (the kind you used at school to make collages and that sort of things) and worked great, i took special care not to let any glue inside the input jack. Tested it and works like a charm.

[pepsi_max2k]

it's not like you *really* need the glue, you can always stick it in a little box or cover it in tape or something...

[tangerine]

You can use the gallery of this forum for uploading samples. Flac files are rather huge though and should only be used when perfect accuracy is necessary. Otherwise well encoded mp3's will do. I'd suggest to create a new thread to discuss the subject in depth.

Thanks GM, the I will make mp3s of the wav and start a topic on repairing process.

I found here some topics reporting the same problem (huge bass and weak mid and highs)

[Billman]

Great Project! I was looking at this microphone from radioshack 270-092C

http://www.radioshack.com/product/index.js...rentPage=search

Would this be a better mic to use?? and if so how would I wire it up?? It has 3wires instead of 2 in greenmachines project.

Edited July 26, 2006 by Billman

[greenmachine]

These seem larger and technically inferior. I'd suggest to get some Panasonic WM-61A capsules from digikey instead if you are in the US:

http://www.digikey.com/scripts/DkSearch/dk...626&Site=US

[mark18]

very cool project. can you recommend some good sites to learn design. i've been looking around and found sites with circuits but nothing that will help one to learn about designing their own. i'd love to see a circuit to record audio to an sd card. put that in an altoids tin and along with your battery box and mics, you'd have the ultimate stealth rig! (i know that's a pretty ambitious project, but i'm willing to learn).

thanks,

mark