greenmachine

How to build a Stereo Microphone and Battery Box

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Figures, the one place I didn't look (digikey) would have them. Thanks for the info :)

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First of all - great thank you to greenmachine!

Really great DIY! Anyway it gave me inspiration as long as i'm waiting for my new unit (MZ-RH910). After that i get my unit i can start live recording and do my first bootlegs at all. ;)

Thank you all guys!

The thing i built. I had to improvise and go without mic-jack, just cord inside the box and out. And i also had to use 11kOhm resistors instead of 10kOhms, but i think it won't matter so much.

[attachmentid=908]

I'll let you know, when i get my first recordings done.

pisialvar, i think you could improve the quality of your recordings if you mount the mics to the outside, even if it might not appear that 'stealthy'. The rim of the glasses seems to cover a bit too much, which could lead to high frequency attenuation and/or nasty resonances. Did you succed with your first recordings? I think i've seen a first recording in the gallery, but can't seem to find it again. Could you post a link or move it to its proper category?

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Hello to all,

I need just a few explanations from those of us that are good with electric wirings and electronic:

1) Does usuall schematics where the FET is operated in common source mode means that capsule is more sensitive to higher SPL so it overloads mic preamp – simply said the capsule is not linear in response to various SPL… or some other situation is involved in here?

2) Someone tried Linkwitz scematics described here:

http://www.linkwitzlab.com/sys_test.htm#Mic

and here:

http://www.linkwitzlab.com/images/graphics/microph2.gif

How those numbers marked with *) – for attenuation values can be explained? It is said here that “value may go up to 100K if the input impedance of the preamp is < 10K”.

Does it means that for atteunation values there it must be placed 100K resistor value, or values described on that hand written schematics, I don’t know what to choose …

Thanks!

Edited by mmilovan

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pisialvar, i think you could improve the quality of your recordings if you mount the mics to the outside, even if it might not appear that 'stealthy'. The rim of the glasses seems to cover a bit too much, which could lead to high frequency attenuation and/or nasty resonances. Did you succed with your first recordings? I think i've seen a first recording in the gallery, but can't seem to find it again. Could you post a link or move it to its proper category?

I got my first recording done and it's here. I also moved it under Live Recordings - Music.

About mounting the mics- i also moved them little bit more down, so they didn't stay so inside of glasses and were more under the thing. So i think that rim wasn't so much on the way, but who knows. Maybe i should move them totaly outside- will see.

Anyway, let me know what do you think about the recording.

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1) Does usuall schematics where the FET is operated in common source mode means that capsule is more sensitive to higher SPL so it overloads mic preamp – simply said the capsule is not linear in response to various SPL… or some other situation is involved in here?

A welcomed side-effect of the mod is the lowering of the mic's sensitivity, thus the preamp can accept higher SPLs before clipping occurs.

2) How those numbers marked with *) – for attenuation values can be explained? It is said here that “value may go up to 100K if the input impedance of the preamp is < 10K”.

Does it means that for atteunation values there it must be placed 100K resistor value, or values described on that hand written schematics, I don’t know what to choose

Instead of attenuating and using the mic-in, the use of the line-in is recommended at high SPLs. Attenuation would only be useful if you don't have a line-in or can't adjust the preamp gain (like some camcorders).

"Attenuation of the microphone output degrades the signal to noise ratio and should only be used, when the preamplifier gain can not be reduced." S.L.

Anyway, let me know what do you think about the recording.

You've got a comment in the gallery.

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A welcomed side-effect of the mod is the lowering of the mic's sensitivity, thus the preamp can accept higher SPLs before clipping occurs.

So, is it non-linearity of the mic capsule to various SPL involved in here, still I can not figure it out?

Instead of attenuating and using the mic-in, the use of the line-in is recommended at high SPLs. Attenuation would only be useful if you don't have a line-in or can't adjust the preamp gain (like some camcorders).

As some members of this forum concluded, mic pre amp gain of HiMD is, again, unadjustable - as I understood rec level adjustment circuit is placed after the preamp - no?

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So, is it non-linearity of the mic capsule to various SPL involved in here, still I can not figure it out?

Could you express your thoughts in different words? I'm not entirely sure what you mean.

As some members of this forum concluded, mic pre amp gain of HiMD is, again, unadjustable - as I understood rec level adjustment circuit is placed after the preamp - no?

This might be true, but you can use line-in for high SPLs without having to worry about overloading it -> no additional attenuation needed.

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I'm sorry I wasn't so clear.:(

I'm thinking of non-linear response of capsule for various SPL. For an example - capsule will produce much higher voltage for loud, punchy sounds (bass drum) and overload mic preamp, and for quiet sounds it will produce not equivalently smaller voltage, right?

Now these words are just my thoughts, I still can't figure how bass drum can be distort...

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I imagine the mics' behavior close to linear up to a certain point - the more the diaphragm swings, the higher the output voltage - ideally a linear relationship, like that:

[attachmentid=970]

Why do you think it could be non-linear?

post-6863-1130013747_thumb.jpg

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I imagine the mics' behavior close to linear up to a certain point - the more the diaphragm swings, the higher the output voltage - ideally a linear relationship, like that:

[attachmentid=970]

Why do you think it could be non-linear?

Well, I'm afraid that my thoughts are just one way of explanation clipped distorsions with bass drums impulses that have much higher amplitude than anything else (other instruments' sounds).

Is attached diagram based on some kind of metering electrical parametars?

I manage to do modifying of monacor capsule MCE 2000 (doing the same as with Panasonic capsule), and do some live recording. While extremly linear in frequency range, loud sounds (for example screaming of persons while excited with someone solo) were still clipped awfully.

Anyone thought of placing DIY limiter or similar kind of circuit before mic-in?

Edited by mmilovan

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For what reason do you refuse to use the line-in if the mic-in can't handle it any longer?

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For what reason do you refuse to use the line-in if the mic-in can't handle it any longer?

Well, one and only reason would be: how to switch without interuptions between mic-in and line-in (and backward) when the music gets louder? How to know precise moment of such switching? Some types of music can be, speaking of quiet and loud passages so different and unpredictable, right?

And for example, if someone decide to use line in plug only, the same clipping occurs in quiet passages below certain points of, let's say, 90 or so db. Sounds below that limit will remain unnoticed, unrecorded...

Edited by mmilovan

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The 96 dB dynamic range of a 16 bit medium should be adequate to capture both (not extremely) quiet and loud passages without excessive noise or clipping without adjusting levels. In extreme cases, like recording the ticking of a clock directly after an indoor heavy metal concert, you should indeed consider to use different settings, but even the rather large dynamic range of recording an orchestra can be done without limiters or different settings with good results (see examples in the galery). Don't overcomplicate simple correlations.

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Don't overcomplicate simple correlations.

OK. So, it is line-in plug a way to go?

Edited by mmilovan

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Simplified it's usually mic-in up to a certain peak SPL (depending on the sensitivity of your mics), for anything above use line-in. Practice doesn't make perfect, but you'll understand correlations easier.

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Hey, that looks like my design!

IPB Image

After opening three 9V batteries (two of them Duracell like the howto) none of them had the plastic case thing, but instead cardboard-backed contacts and cheap, thin plastic wrapping. So I had no choice but to use this design, and it's worked very well.

Instead of hot gluing the whole thing, I just put duct tape over the components as I wasn't sure how hot it would get (not very, but I didn't know if I had shorted anything) but I do plan on covering it all in glue now.

The first recording was at a heavy metal show. Not the loudest show I've been to, but I got good results with very little clipping standing just behind the soundboard. But the sensitivity of the capsules is noticably different so I'll have to match a pair.

Thanks for the howto greenmachine!

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Very nice. The capacitors look somewhat large-ish, don't they?

Be sure to loop the cable around the board before finishing it and be careful that no glue enters the jack.

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Well, I've done it also. Thanks to greenmachine for this great diy (and a little extra help). I have posted a song from my first band recording. It's a local metal band. It was very loud, and I could pick the mix apart, but I think the recording turned out great. Please take a listen and let me know what you think.

[attachmentid=1209]

post-23078-1134016753_thumb.jpg

Edited by woulfer

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i made a diy battery box and encased it in a radio shack project box, but i like your design better because the project box is just too bulky to carry around. well, that and my friend decided we should put a big red button switch on it so it sorta resembles a bomb detenator. getting caught sneaking gear in is one thing, but now my biggest fear is having to explain why i have this sketchy device on me. anyhoo, question for the floor: how long (approximately) does your 9v battery last? do you put a new one in before each show?

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Assuming that the microphones consume less than 1mA and battery capacity of an Alkaline is in the ~300-500mAh region, the battery should last about 300-1000 hours. I put in a new one once the voltage drops below 7V or so. If you don't constantly use it, it should last at least a year or so. Putting in a new battery before each show is a waste.

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Hey guys. Check out my new diy battery box. It is housed in an Altoid's Gum tin. It's the perfect size (not much bigger than greenmachine's), and I feel more comfortable that it has some protection.

[attachmentid=1272]

[attachmentid=1273]

post-23078-1135876294_thumb.jpg

post-23078-1135876349_thumb.jpg

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So, I'm trying to make both a battery box and a pair of binaural mics (with panasonic mce2000 caps). I'm a noob on this area, this will be my first experience with soldering and putting an electronic device together.

I'm basically facing 2 material problems. first I've found it hard to find the 3.5 mm stereo connector with the cable as shown on the pics on the first page. I've cut open a (bad quality) pair of earplugs but it didn't look like cable on the pic. Maybe someone could point me in the right direction on where to find these. I've got some 3.5mm jack > dual mono RCA cables lying around, would these contain the cable needed?

Second I just noticed I've only got 0.25W 10 kOhm carbonfilm resistors. Could I use these instead of the metalfilm resistors? What will be the difference?

Thanks in advance

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So, I'm trying to make both a battery box and a pair of binaural mics (with panasonic mce2000 caps). I'm a noob on this area, this will be my first experience with soldering and putting an electronic device together.

I'm basically facing 2 material problems. first I've found it hard to find the 3.5 mm stereo connector with the cable as shown on the pics on the first page. I've cut open a (bad quality) pair of earplugs but it didn't look like cable on the pic. Maybe someone could point me in the right direction on where to find these. I've got some 3.5mm jack > dual mono RCA cables lying around, would these contain the cable needed?

Second I just noticed I've only got 0.25W 10 kOhm carbonfilm resistors. Could I use these instead of the metalfilm resistors? What will be the difference?

Thanks in advance

1) I found them in a local electronics store and have a few left. PM me if interested.

2) These usually have somewhat greater tolerances (+-5% instead of +-1%). Actually it makes very little difference unless you do it professionally. You can use them without thinking twice. If you have more than two of them, you can use a mulitimeter to match them by yourself.

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I'll just use those carbon film resistors then. Thanks for the offer on the cables. Tho, I just cut open one of the jack > dual mono RCA cables and those are the ones I need, so it won't be necessary for you to send me the cables. I'll post some pics when I'm finished, which will hopefully be at the end of next week since I still have to receive some parts I ordered.

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a while back i inherited a pair of audio technica mini cardioids, at831c's to be exact. they came with no power module, and terminated in mini-xlr plugs. i've played around with them with my sony d7, and with or without phantom power (there seems to be little performance difference that i've noticed. it's been a while since i've used them with phantom power, though, so i could be remembering this wrong. the last show i used them with pp was coldplay in 2003. now that i think about it, it seems with pp the recording suffered from much less clipping.), by themselves they overpower the mic-in for most shows, and don't quite push enough for the line-in. my question is, instead of getting some electret capsules and making my own mics, could i use the at's with your battery box? i'd really like to come up with a sleek solution with the at's, since they're obviously higher quality than i could make myself (one day i'll track down and invest in a matched pair of omni caps to swap out when i want to. it was quite a pleasant surprise to find the heads unscrewed.), but i don't want to risk damaging them. i lost the pp supply and have since rigged up a variable line attenuator to keep the clipping to a minimum through the mic imput.

and one day there will be a non-ipod linux solution to line-in recording with my ipod video, and i'd like to have these usable with that as well. any help/advice you have would be very welcome.

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