How to build a Stereo Microphone and Battery Box

[A440]

i'd love to see a circuit to record audio to an sd card. put that in an altoids tin

Wouldn't we all?

Unfortunately, that's not a circuit, that's an analog-to-digital converter plus controls plus hardware to write the data to the SD card, and, by the way, won't you want some kind of display with that?

The device exists. It's bigger than an Altoids tin.

http://www.rolandus.com/products/productde...px?ObjectId=757

There are also small flash memory recorders made by companies like iRiver, and pocket hard-drive players that double as recorders. Someday, perhaps soon, one of them will be as reliable, high-quality and recording-oriented as minidisc.

[CHURCH-AUDIO]

And now you’re qualified to say that my preamps distort at concert levels???

WOW..... Now you’re qualified to say that a preamp is not necessary for concert recording???

Man I don't get people that have been doing it for 2 months, can come along and bash people that have been doing it for 10 years, And pretend to know more about mics and concert recording then a sound engineer with over 20 years in the business. Can you Please explain this to me? I would love to hear it.

Hehe, nice to see someone actually doing it, i'd like to see more people giving it a try. Looks pretty good for a first attempt. Actually, the resistors should usually be somewhere in the 2-10kOhm range, but you're right - it doesn't matter much.

A few months ago when i joined here, i had no idea about all this - what a good microphone should look like, how it should be placed - i didn't even have the slightest clue what a battery box is or what you could need it for. But i knew about Minidisc's high quality recording capabilities and wanted to use it for live recording. Music is an important part of my life, why not conserve some of it?

I started experimenting with some older microphone capsules i had lying around from disassembled tape/radio recorders soon. The first results were promising, but the recording came out clipped above a certain loudness. So i started researching if there are possibilities to avoid it. What i found was the (simple) headphone attenuator and the battery box. I went for the simpler solution first which gave a slight improvement at high SPLs but realized soon that this design has some serious limitations. So i gave the battery box a try. I had some serious problems to find a small yet durable design, the first try was really awful, rather large and too fragile. But i realized that this kind of external powering of the microphones is the way to go for undistorted recording at high SPLs. At the same time i discovered the very welcomed source follower mod which i use for serious recording ever since. Spending lots of thoughts about optimized designs, some less successful attempts and testing various microphone elements finally lead me to these two designs, as illustrated above. I'm a happy recordist ever since.

Thank you all for your kind words, i'm glad to help.

Edited August 18, 2006 by CHURCH-AUDIO

[pepsi_max2k]

gee, what is with people this week? i'm seeing nothing but angryness on message boards...

just think, if people didn't try to improve on other's products, we'd still be listening to vinyl.

fwiw, i've read a lot of this thread and didn't notice anyone criticizing any particular brand of mics/amps. so it can't be that bad.

[raintheory]

yeah I'm not sure I follow you Church... Firstly that thread you're quoting was from almost a year ago... and second, I don't see where there is anything said that would make you feel this way...

I'm sorry if theres confusion in the air here at the moment, but rest assured I know the regulars here and I highly doubt any of them are trying to make your projects look bad in any way. Personally I have seen your work and am very impressed.

[greenmachine]

I can't give technical explanations, but speak from experience.

When recording quiet sounds, the built-in preamp of a (Hi-)MD usually gives very nice, quiet enough (no significant noise) recordings. No additional gear necessary (except for microphones). Below a certain level setting (low sensitivity, approx. 10/30 for my NH700) you can't reduce distortion any further no matter how low you set the levels. This is the point where you should switch to line-in (via battery box).

You obviously don't record quiet sounds via line-in, otherwise the levels will be very low and you'll get an incerased noise floor after normalization. If the to be recorded signal is strong enough to go line-in though, there should be no audible/significant noise unless you manually set the levels way too low.

If your recorder lacks a built-in preamp, a battery box is obviously no substitute for an external preamp when recording quiet sounds. In my experience, a recorder equipped with a high quality preamp (like most (Hi-)MD recorders nowadays have) and line-in requires nothing but a battery box (and microphones) to cover the full range from recording quiet to very high sound pressure levels.

[beefstew]

How to build a miniature battery module / box:

Other parts needed: a small piece of circuit board, two 2.2uF capacitors, two 10kOhm resistors, preferrably 1% metal film, one 1/8" / 3.5mm stereo jack, one cable with a 1/8" / 3.5mm stereo connector. Solder the parts to the circuit board, as seen in the schematic, the stereo jack belongs to the side of the mic input, the cable with connector to the output side. If the jack is not a closed type, wrap some tape around it to prevent glue entering the inside. Solder the board to the battery connector. Fill the gap with hot melt glue. Cut a piece off the top plastic shell so that there's place for the jack. Loop the cable around to the opposite side of the jack so that there's no stress on the connections when in use. Put the top shell on it and fill the gap with hot melt glue.

What stores have these kinds of parts??

[greenmachine]

What stores have these kinds of parts??

Most electronic parts stores, like digi-key in the usa or conrad electronics in germany. If you can't answer this question for yourself and have no experience with electronics/soldering, this propably isn't the right project for you.

[beefstew]

Most electronic parts stores, like digi-key in the usa or conrad electronics in germany. If you can't answer this question for yourself and have no experience with electronics/soldering, this propably isn't the right project for you.

no its just that i live in a small ass town (in the usa) with like no stores with this stuff

[A440]

http://www.digikey.com/

[greenmachine]

You can order the parts online there, they will ship it home to you. Or you could disassemble some defective electronic devices in your home and see if you can get the parts from there. Good luck with it and let us know if you succeed.

[beefstew]

You can order the parts online there, they will ship it home to you. Or you could disassemble some defective electronic devices in your home and see if you can get the parts from there. Good luck with it and let us know if you succeed.

yeah ive taken apart some busted cd players and tape players but all those little pieces look alike - could u post some close up pics of the resistors and stuff?

[bravoland]

i'm interested in giving this a try.

where can i buy miniature electret microphone capsules?

[A440]

I think I'm having deja vu.

http://www.digikey.com/

[bravoland]

sorry... i didn't see the 13 or so other pages of information.. digikey seems to be out of the wm-61 right now.. any other name brands capsules anyone recommend?

[greenmachine]

sorry... i didn't see the 13 or so other pages of information.. digikey seems to be out of the wm-61 right now.. any other name brands capsules anyone recommend?

I like the Monacor MCE-2000 (google it) as well, but don't know if they're available outside of europe. They're also more expensive.

yeah ive taken apart some busted cd players and tape players but all those little pieces look alike - could u post some close up pics of the resistors and stuff?

A resistor color chart like this might be helpful to choose suitable resistors:

[attachmentid=2030]

[CommanderZero]

i have a electret microphone, its a stereo one, it has ground/L+R. i have 2 of these, so can i just solder off the left wire on one side and the right channel on one side, and use them like that?

[A440]

digikey seems to be out of the wm-61 right now...

They're baaaaack...

http://www.digikey.com/scripts/DkSearch/dk...582&Site=US

[fishstyc]

Hi,

I ordered these microphones: SP-TFB-2 - SOUND PROFESSIONALS - LOW NOISE IN-EAR BINAURAL MICROPHONES

Would your battery module work fine with these (that is, it will sound good and won't harm the mics)?

Thx.

[tiberiusbeekirk]

I want to thank Greenmachine for his tutorial again.

I just made a T-style mic as a carry around mic for those times I find myself needing to record something. I've found it easier to make a T style mic than a dual mono type mic going into a 3.5mm stereo plug. My soldering is getting better.

The panasonic wm61's fit perfectly into a Bic Round stic pen.

I just ordered the parts for your battery box. I hope I can do it. I want to thank Tangerine for his helpful schematic.

If anyone is interested, my first binaural recording is up in the gallery section.

Your comments are most welcome.

edit, rec'd the parts today. My goodness, those resistors are tiny and I ordered the wrong PC board, it holes are smaller and spaced tighter. How do I cut these to size?

found out why the resistors are so small, I ordered the Panasonic 1% metal film MINIATURE ones.

take two, I finished it. however it's not the way it is per the DIY.

My first try only had sound in the right channel, then my second try had no sound to both channel.

So I deviated from the photos of GM's BB and went with Tangerines block diagram. I just used some wire to go from the input to the Caps and resistors.

It works, I'm working on my second one.

Edited October 17, 2006 by tiberiusbeekirk

[fishstyc]

If you want to record high sound pressure levels (like amplified music/instruments, concerts, everything you would call 'loud') without noticable distortion, you should use the line-in of your recorder. The line-in uses a significantly lower preamplification than the mic-in, which would overload soon at high SPLs. The line-in provides no bias voltage ('plug in power') for the microphones though, thus the microphones need to be powered externally, which is the task of this module.

Thanks for the tutorial.

Here's another question (I don't really have a lot of electronics experience):

The battery module only powers the microphones, but if I understand correctly, with a higher voltage than what the minidisc sends to the mics. This would also be one of the reasons that the microphones can stand a higher SPL.

I thought that the impedance of the input had an effect on the sound of the microphone. So what happens to the characteristics of the mic if you connect it to the line in, via the module? And what would be the effect if you connect the battery module to the mic-in? Is it harmful, will it overload the mic-in, or can you just turn it down, will the mic-in sound diferent than the line-in (I heard people talk about too much bass, may this be a reason)?

Does the battery module itself change the characteristics (frequency response curve) of the mic (apart from SPL at which the mic overloads).

Many questions I know. Thanks if someone can help me out on a few of these (I didn't read the whole thread so I apologise if someone already answered these).

[Malcolm Stewart]

Here's another question (I don't really have a lot of electronics experience):

The battery module only powers the microphones, but if I understand correctly, with a higher voltage than what the minidisc sends to the mics. This would also be one of the reasons that the microphones can stand a higher SPL.

I thought that the impedance of the input had an effect on the sound of the microphone. So what happens to the characteristics of the mic if you connect it to the line in, via the module? And what would be the effect if you connect the battery module to the mic-in? Is it harmful, will it overload the mic-in, or can you just turn it down, will the mic-in sound diferent than the line-in (I heard people talk about too much bass, may this be a reason)?

Does the battery module itself change the characteristics (frequency response curve) of the mic (apart from SPL at which the mic overloads).

Many questions I know. Thanks if someone can help me out on a few of these (I didn't read the whole thread so I apologise if someone already answered these).

I've knocked up a battery box (as per this thread) and using the same small omni microphones, all I've noticed is how clean the recordings are, albeit at a lower level than via the mic input, naturally. (RH-10 and RH-1)

Connecting the battery box output to the mic-input is OK. The 9V only goes to the mics themselves, and the output is isolated. There's no amplification in the battery box. Whether the electronics in the mic gives a little more gain with the higher voltage, I've no idea.

Extra bass often comes from having the mic closer to the sound source - something which a higher dynamic range may encourage.

I suggest you just get the parts and give it a go. I'm sure you won't be disappointed. If you then find that you are concerned about the frequency response, there are plenty of tools available for dealing with that when you've uploaded to your PC.

[fishstyc]

I've knocked up a battery box (as per this thread) and using the same small omni microphones, all I've noticed is how clean the recordings are, albeit at a lower level than via the mic input, naturally. (RH-10 and RH-1)

Connecting the battery box output to the mic-input is OK. The 9V only goes to the mics themselves, and the output is isolated. There's no amplification in the battery box. Whether the electronics in the mic gives a little more gain with the higher voltage, I've no idea.

Extra bass often comes from having the mic closer to the sound source - something which a higher dynamic range may encourage.

I suggest you just get the parts and give it a go. I'm sure you won't be disappointed. If you then find that you are concerned about the frequency response, there are plenty of tools available for dealing with that when you've uploaded to your PC.

Thanx for your insights.

I already made a battery module, but my first impression (apart from the noise which probably has to do with my soldering skills), was that the sound was a bit 'empty', clean indeed but lacking warmth (I used line in with the battery module).

So I'll have to experiment some more (connecting the batt module to the mic in and see what that does to the sound). I may go for an external mic amplifier one day, because the one in the MD gives a lot of noise.

Apart from that I am extremely happy with the binaural mics themselves. Whithout batt module, this recordings were the first where I didn't feel the need to start equalizing immediately, because the sound was not OK.

[Top Cat]

I may go for an external mic amplifier one day, because the one in the MD gives a lot of noise.

Are you sure it's the mic pre-amp which makes noise?

Keep in mind, most mic cartridges rarely deliver SNR greater than 60 dB, which is probably some 20 dB less than that of Sony's built-in pre-amp

[Malcolm Stewart]

Are you sure it's the mic pre-amp which makes noise?

Keep in mind, most mic cartridges rarely deliver SNR greater than 60 dB, which is probably some 20 dB less than that of Sony's built-in pre-amp

For fishstyc

I was going to make the same point. Occasionally, the noise level has been so low that the automatic Track marker has kicked in. Can't remember which Hi-MD recorder I was using. (On the contrary I have found it quite difficult doing wild-life recordings of, say, birds, very difficult without picking up distant road noise, aeroplanes etc.)

[fishstyc]

Are you sure it's the mic pre-amp which makes noise?

Keep in mind, most mic cartridges rarely deliver SNR greater than 60 dB, which is probably some 20 dB less than that of Sony's built-in pre-amp

Quite sure (tell me if I make a huge mistake here), since I recorded a few seconds with just a very short unconnected wire plugged in to the mic input (so my md recorder would say 'mic recording'), instead of a microphone and the amount of noise is very audible I think. I didn't really hear a difference with the mic plugged in (noise-wise), so it seems to me that the noise floor of the pramp is a lot higher than that of the mics I have.

That's my personal feeling though of course.

[Top Cat]

Quite sure (tell me if I make a huge mistake here), since I recorded a few seconds with just a very short unconnected wire plugged in to the mic input (so my md recorder would say 'mic recording'), instead of a microphone and the amount of noise is very audible I think.

That might be the interference picked up from the air.

To reduce external influence the wires should be bridged by something similar to a mic, may be a resistor

[tiberiusbeekirk]

Is there a reason to use the Battery box through MIC in, instead of LINE in?

[RockyJ]

I'm going to build a BB and do some testing to see if running soft sounds is much different going through a preamp or going through the BB and post-normalizing the digital output. There will be some resolution loss though it may not matter.

I am guessing the mic will put out analog signal noise regardless of being run through a preamp or line-in and can't be avoided. However you are avoiding preamp noise going through the line-in, I just don't know if post processing low signals will be a good tradeoff for the bother and problems with preamps.

[RockyJ]

I got Radio Shack's non polarized caps, is that acceptable.

[greenmachine]

Is there a reason to use the Battery box through MIC in, instead of LINE in?

The mics will perform slightly better in theory with a higher voltage [s/n, response, sensitivity], but the differences are subtle. Plug in power should be sufficient most of the time.

I'm going to build a BB and do some testing to see if running soft sounds is much different going through a preamp or going through the BB and post-normalizing the digital output. There will be some resolution loss though it may not matter.

I am guessing the mic will put out analog signal noise regardless of being run through a preamp or line-in and can't be avoided. However you are avoiding preamp noise going through the line-in, I just don't know if post processing low signals will be a good tradeoff for the bother and problems with preamps.

When you record at low levels you will get additional digital noise after normalization, not just resolution loss.

I got Radio Shack's non polarized caps, is that acceptable.

Some people claim non-polarized ones to be sound-quality-wise superior, but since i can't tell a difference, i've used polarized ones because of their size/shape.

[tiberiusbeekirk]

Someone on another board opened a commercially made BB and it appears they were using metallized film caps. At least, that's what it looks like they were to my untrained eyes, they were yellow, with axial leads and took up a lot of space in the box.

[kentek]

How to build a high quality stereo / binaural miniature microphone:

Get the parts for example at www.digikey.com or www.conrad.de.

Required parts:

- 2 omnidirectional miniature electret microphone capsules (get the best ones you can find - your selection will have a major influence on the sound quality - recommendation: Panasonic WM-61, Monacor MCE-2000)

- 3.5 mm stereo connector with cable, preferrably shielded

- a few inches of heat shrinkable tubing, slightly larger diameter than the capsules

Additional requirements:

- soldering iron + solder

- hot melt glue + gun

- scissors

Warning: Be very careful if you apply heat to microphones, it could irreversibly damage the diaphragm. Keep the procedure(s) as short as possible.

1) Skin and solder the cable to the capsule, the shield to the outer shell of the capsule, keep soldering time as short as possible. (heat)

[attachmentid=475][attachmentid=463]

2) Bend the cable and add some hot melt glue. (heat)

[attachmentid=464][attachmentid=465]

3) Cut suitable pieces off the heat shrink tube (about 1/2 inch) and put it over the capsules.

[attachmentid=466][attachmentid=468][attachmentid=467]

4) Heat it with a lighter or similar tool for a short time just until it doesn't shrink any further, remove leaking glue as long as it is fluid. This process requires some experience. You might want to practice first. Never apply excessive heat to a single spot, keep the heat source moving.

[attachmentid=469][attachmentid=471][attachmentid=470]

For a realistic stereo image it is important to separate the mic elements about 6-8 inches and preferrably have a separator in between, which is ideally your head. You can attach the microphones to the rim of glasses using the same heat shrink tube method, put them into eye glass retainers (croakies) or just use black electrical tape. Don't mount them too far up front or you'll loose a great part of the head's separating characteristic. Having them as close as possible to your ears is ideal.

[attachmentid=909][attachmentid=912][attachmentid=910]

How do I wire it up if the mics have 2 wire plus a ground?

[fishstyc]

Is there a reason to use the Battery box through MIC in, instead of LINE in?

The reason I think people want to use the LINE IN is to avoid the mic preamp (so that it can't be overloaded when recording loud signals and to avoid adding the extra noise it may generate, if I understood correctly).

The thing is, I suspected that the sound would also be different if you recorded the same thing via line in. This has been confirmed by some test recordings I made.

The sound via MIC IN is nice and warm, the sound via LINE IN is thin and hard. Very ugly to my ears. My personal conclusion is that I will never record with the battery box directly through LINE IN, but I will always use the MIC IN. A nicer sound is far more important to me than some noise, and even a slightly distorted mic to me is less of a problem than the ugly sound I get when using line in directly.

But you should try it out for yourself of course...

[alchemy]

Thank you very much for posting these instructions greenmachine.

My question for you is if this homeade battery module will work with the Sound Professionals SP-BMC-2 microphones, seen here:

http://www.soundprofessionals.com/cgi-bin/gold/item/SP-BMC-2

I was hoping to use them, the DIY battery box, and then plug into the line in on my Sharp MD MT-90.

Also, I noticed my MD recorder has an optical in, is there any way or benefit to do an optical out on the battery module?

Thank you in advance for any responses.

Edited October 29, 2006 by alchemy

[greenmachine]

The battery module should work with any standard pre-polarized condenser [electret] mic [like the sp-bmc-2] unless it is modified and requires reverse polarity [rare, very unlikely]. Adding an optical out is not quite an easy task since it would require a built-in analog t digital converter [ADC].

[tiberiusbeekirk]

Is the mod you're talking about where I cut the trace for the Ground and use the other pad as ground making a connection to the outside edge of capsule and the original cut ground pad as (+)?

Would your DIY battery box work with this mod? Only because I just made this mod with some short lead wires just now.

[RockyJ]

<p>I know people are always looking for other container ideas for GM's

bat box so I took some pics of my project. Hope it is useful. </p>

<p>I found the batbox definitely improves the mic-in in at least

one aspect, and after I try some recording may find it better than

my external commercial preamp/line-in combo. The commercial preamp

has problems I can't figure out, sometimes it clips at approx -3db,

and it also has a jack I can't completely trust. Also with the on

switch and low/hi amp switch, I guess they could add noise to the

mix, so if this batterybox/mic-in performs like it is starting out,

I will definitely recommend it for use with mic-in.</p>

<p>The one improvement I noticed is the balance levels between

channels. with mic-in there is a 3db difference between channels,

but with the batterybox they are even levels.</p>

<p>The mic-in set at 20/30 equals the batterbox's setting of

16/30.</p>

<p>After looking for a good case in lieu of the glue glob, since I

wanted to do jacks instead of the hardwired output, I came up with

a floss container. Here's some pics.<br>

<br>

</p>

<table BORDER frame=box RULES=all>

<col valign="top" align="center" width="30%">

<col valign="top" align="center" width="30%">

<col valign="top" align="center" width="30%">

<tr>

<td><p>After I glued it I forgot what side was the mic. Good thing I

took the pics Be sure and mark the mic on the resistor jacks</p></td>

<td><p>use the floss for something </p></td>

<td></td>

</tr>

<tr>

<td><p>drill 1/4" holes, the plastic is soft enough to do by hand but

protect your fingers with some tape</p></td>

<td></td>

<td></td>

</tr>

<tr>

<td colspan=2><p>I stripped the grnd(-) a little long and used the extra length

to bridge the two jacks. If I do it again, I will add a separate

bridge wire to allow for expansion and flexibility when mounting in

the container.</p></td>

<td></td>

</tr>

<tr>

<td><p>I mounted it on the outside to work on. This gave me some idea

of final position as I attach the caps</p></td>

<td><p>Nut the jacks and add some glue to keep wires separate. I put

some elect tape pieces over the jacks and also between areas I was

worried about shorting. I forgot to get pics of the resistor

attachment but their leads will fit in the jack's solder tabs along

with the cap leads to make an easy connection.</p></td>

<td></td>

</tr>

</table>

<p>You can poke some holes in a patch of tinfoil and wrap the

container with the jacks sticking thru the holes and the nut on the

outside. I would suppose this would add some shielding tied to the

grnd(-).</p>

<p>I salvaged the bat connector from an old garage door opener.

Check local dealers they may have some old throwaway openers from

their jobs.</p>

Edited January 1, 2007 by RockyDisc

[beefstew]

well im looking at DigiKey

and im searching for

two 2.2uF capacitors, two 10kOhm resistors, preferrably 1% metal film

and i did a search for "2.2uF capacitors"

and it gave me tons of options for this!

what kind do i need? will any 2.2uF capacitor work?

Also i tried looking for the 10kOhm resistors - but there are many many variables as well...i dont which one to choose!

if someone could copy down the part numbers for the specific piece used... that would be awesome!

thanks for the great DIY

hopefully i can finally get one finished

Edited December 9, 2006 by beefstew

[Nathan P]

Okay, my box and mic work well but no matter what I do, the left channel is always maxing out, and the right is quiet. Is it my battery box? My mics? I replaced both the mics, and the left is still considerably louder. Note that I didn't match the mics, but what are the chances of it being that far off with 4 different mics, twice in a row and the same orientation? (Left louder)

[Nathan P]

Well, found my own problem I wired up the ground as left channel because I looked at the pinout on the plugs I bought backwards. I may just make some adaptors, it would be cheaper and easier than trying to unglue the whole thing. To make another one I need one miniplug socket and 2 caps, which is like $3, so I'll probably just buy another set of parts and just build another one.