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Old 7th April 2003, 11:27 PM   #1
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Default High Quality mic amplifier for Panasonic WM-60a electret?

I was experimenting a little with Panasonic WM-60a electret capsule and
decided to put everything into a small metal box and supply with batteries,
so that I can record and measure outdoors.

It will be used for measuring loudspeakers, recording voices and whatever
possible regarding directional characteristic of electret capsule.

I'am looking for some high quality solution so I plan on using a BurrBrown
INA217(same as SSM2017), symetrical supply out of two 9V batteries, and
another 9V battery for microfon bias voltage.
Capsule is going to be modified as suggested by Linkwitz. I'am not sure
wheather I should implement schematic B or C? Which are the advantages /
disadvantages of circuit B over C vice versa?

Click the image to open in full size.

Am I missing something?

Is there a possibility for a simetrical supply for OP to create problems?
Lets say one battery after some usage gives 7.5V for a plus rail and the
other -7V for the minus rail........ I don't know how to express myself
better in english

I'am going to use standard 9V acumulator bateries (I have 3 of them),
but is it possible to achieve the same final results using 2 bateries?
Wondering, wondering....

tnx for all replays,
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Old 8th April 2003, 01:55 AM   #2
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The first DIY preamps for this electret were the two Mitey Mike versions:


On above's URL you will find the MM2 and the MM3 (which I didn't know about).

An easier alternative is the corrected "El cheapo" mic preamp, which uses through hole parts:


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Old 8th April 2003, 02:12 AM   #3
BrianL is offline BrianL  United States
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I don't see the need for a differential-in part like the
INA217/SSM2017. You don't have an inherently differential
in the Panasonic mic, so a normal low-noise op-amp will

There shouldn't be a whole lot to designing a preamp
for this. The Mitey Mike preamp was designed for measurement
applications and might not ring your audiophile chimes
of you're using it for music recording.
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Old 8th April 2003, 04:33 AM   #4
Pedja is offline Pedja  Serbia
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Hello Mario,

Basically it doesn’t matter what connection you’ll use, that FET will be polarized the same way in both cases. Circuit B can be considered as customary, circuit C is the same thing but uses only two wires. If you’ll go with circuit C take note on the battery’s polarity.

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Old 8th April 2003, 10:09 AM   #5
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Default pre amp´s for wm 60 capsule


It you are trying to replace the build in fet for even lower self noise.
let me know if you get better result. I havent tryed.
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Old 8th April 2003, 05:15 PM   #6
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Well I'am going to measure loudspeakers, record male vocals and acoustic guitar for now.
I would like it to be as transparent as possible with WM60A electret, capable of lets say
110db without clipping and high distorsion, have good frequency response and also as
fewer parts as possible.

I'am going to modify the electret capsule as sugested on Linkwitz web site and hook it on
some OPAMP as shown on the figure B.

I though that INA217 would be nice couse it is a complete solution in one integrated chip,
so that I need only few external parts.

I'am also going to put a switch so that I can chose high gain or low gain setting.

I looked at ESP web site and above posted links and still prefere something with fewer parts.

thanks for all the help so far,
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Old 8th April 2003, 05:31 PM   #7
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I forgot to say that I have INA217 on hand. A frend told me that I can get it from him for free.
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Old 9th March 2004, 11:46 PM   #8
Ryssen is offline Ryssen  Sweden
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I was going to build a mic amp like MM2, in the link above,but I can´t find the IC´s, MAX402-438, could anyone suggest a replacement.
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Old 10th March 2004, 06:29 PM   #9
Ryssen is offline Ryssen  Sweden
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I have some OPA637,can I use these,If I use 2 9volt bat. +- 9 volts,or can it be driven with only 9volts?Someone must know.(I hope).
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