condenser mic school project

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12afael

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Aug 6, 2004
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well here is the story , my brother ask me if I could build a mic . I say sure. he have to do a project for his technology class.

we build a kind of condenser capsule using a chocolate wrapper made of plastic and a film of aluminium (this is a CHHHHHEEEAAAAP mic). is not so thin like a real membrane but it should work.
the back plate is a piece of clean pcb.the distance between the film and the back plate is like 1,2mm and the ratio of the capsule is 3,5cm.

I put 10 9volt bateries for get 80Volts for the capsule. I don`t have 1G resistors so I put 5 of 22M so I have 110M as polarization of the capsule.

as amp I put two 1000 time gain with two op amps(1.000.000 times!!!), we don`t need balanced stuff.the op amp work with another 9v batery.

the problem is that we have VERY low output. I have to normalize the wave to hear something between the noise. it sound clear but with noise I think the signal to noise ratio is catastrofic.

some one have an idea of how improve this mic?
 
[quote author="12afael"]well here is the story , my brother ask me if I could build a mic . I say sure. he have to do a project for his technology class.

we build a kind of condenser capsule using a chocolate wrapper made of plastic and a film of aluminium [/quote]

Maybe the problem is the thickness. Plastic wrap is maybe 2 or 3 mills I think which is ~50 to 75 microns and my condenser mic has a 6 micron diapragm.

I'm just guessing... I never built a capsule before.

Kiira
 
I will try to improve the spacing between the diaphragm and backplate.
is the paper of filter caps more thin ?

is the polarization resitor so critical?
 
> the distance between the film and the back plate is like 1,2mm

WAY too big. IIRC, sensitivity rises as the inverse of the square of distance. So a 0.001" space would be about 2,500 times more output.

However 0.001" or 0.025mm spacing across a 35mm diameter will force you to tension the chocolate wrapper so it never touches the backplate. And your backplate must be flat to much less than 0.001" (can't use an old penny).

The thickness of the membrane is not so very critical if it is mostly light plastic. The metal should probably be on the backplate side to minimize the distance (mikes can be built with metal on the outside but that's tricky with candy technology).

Get some very thin stiff plastic. Maybe like a "sheet protector" used for holding important and often-used paper in an office binder. Cut a ring 35mm outside and 30mm inside. Get some Crazy Glue (cyanoacrylate) instant glue, the good stuff not the weak stuff that won't stick fingers together. Glue the ring to the backplate. Glue the candy-wrap to the ring. Get it reasonably tight while the glue sets. Then touch it with hot-air from a hair dryer to shrink the candy-wrap taut.

One problem can be: that metallized coating may not be continuous, especially after being wrapped and un-wrapped from the candy bar. Contact to metallization can also be tricky.

A different technique is a Snell transducer. Use very coarse sandpaper to rough-up the backplate. Lay the candy-wrap on the back-plate metallization side away from the backplate. The low-spots in the roughened surface are the active areas. The high spots are acoustically dead, and are parasitic capacitance. But no explicit gap is needed, and the plastic-film provides insulation. The film's self-stiffness in bridging the small gaps between high-spots sets the resonant frequency, which will be spread-spectrum because of the random distance between high-spots. (Crown's early PZMs used a similar diaphragm plan but the high-spots were micro-molded in a regular grid.)
 
I don't have anything to contribute, but this is very interesting and I really hope you can get your truly DIY condenser working. And I'd love to see a picture of the build. Good luck :thumb: !
 
I reduce spacing between the diaphragm and backplate with better results.
but still is very poor the signal.
I think that the membrane is not enought thin.
here are pictures of the ugly capsule , the most ugly capsule on the history.
it is made with a coffee can , good smell :wink: it could make a singer song better???? :cool:
a "bon o bon" mmm chocolate , I could do thousands of mics with these wrappers .and a pcb







finally we build a electret based mic. maybe in the the future will experiment with other membranes. I think some like this could work well for heavy sounds like guitar amps.
 
here is my humble capsule experiment,i have to reskin it,and build the head amp,i received some 1 g resistors this week...


http://community.webshots.com/photo/499522898/499536196PWiIBP#


http://community.webshots.com/photo/499522898/499537537UPozHk#


http://community.webshots.com/photo/499522898/499540411MPLobf#

http://community.webshots.com/photo/499522898/499541874coGtdq#

http://community.webshots.com/photo/499522898/499543416jkJEWM#

http://community.webshots.com/photo/499522898/499546235jhIqGp#



http://community.webshots.com/photo/499522898/499548664OsxiFb#
 
what are you using as membrane?
it look like the capsule of an old pdf article.
great job.

Pd: I will do reverse ingeniering of your loopers with this pictures.
just kidding. :grin:
 
I find this very encouraging,proper DIY !
infinitly preferable to trying to modify commercially made rubish.
Keep going.
Andy.
 
HI!
I'm using the metallized film from a capacitor,following advices from the guru's from here...the mechanical building was posted by Nothsiderap some time ago,congratulations to his work,and thanks for his help...i hope i can make it sound....
 

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