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Author Topic: Microphone tester  (Read 2703 times)
ELMER
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Posts: 18




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« on: October 13, 2012, 06:41:07 PM »

Could someone point me to a tutorial/plans on building a tester for microphones?
I know they sell them for $50, but I would like to build my own.
Thank you
I did search the site and google first.
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KD0REQ
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Posts: 1006




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« Reply #1 on: October 13, 2012, 08:57:14 PM »

if you can get 60 dB gain, you can drive earphones.

just about any inverting op-amp in any spec sheet can be tickled up there, or you can cascade two amps at 30 dB each, and hook that to a set of cans.

if all you are looking for is gain, and not quality, plug the mic into the magnetic phono input of a stereo receiver and earphones into the other.  the RIAA equalization will make it sound like a cricket, but it's go-nogo for zero investment.
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K7MDO
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Posts: 325




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« Reply #2 on: October 14, 2012, 06:52:14 AM »

Couldn't you get a lot of information with a oscilloscope? It seems like first you might need some "standard"data for the different types of microphones.  Just a thought.
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K8AXW
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Posts: 3963




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« Reply #3 on: October 14, 2012, 07:04:45 AM »

I use my old Heathkit audio signal tracer.  Just connect the mic to the signal tracer probe with the gain turned down and then speak into the mic as I advance the gain.

It's a go-no-go method which tells you nothing about the impedance of the mic. 
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G8JNJ
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« Reply #4 on: October 14, 2012, 11:15:30 AM »

Hi,

If you have a PC with a soundcard you can test microphones.

Connect the microphone to the soundcard mic input and use something like Soundcard Oscilloscope to check the sensitivity.

http://www.zeitnitz.de/Christian/scope_en

You can also use the audio signal generator function and a set of Hi-Fi headphones to check the frequency response of the microphone. Set the audio generator to sweep mode, and take a look at the spectrum analyser plot.

You may need to experiment with volume settings, mic / headphone placement and room acoustics to get the best results. But you can get a good idea of the response curve fairly easily.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com
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ELMER
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Posts: 18




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« Reply #5 on: October 14, 2012, 05:01:42 PM »

Gentlemen, thanks for all the help. I was just looking for a diagram on building a homemade box to plug my 4 pin and 5 pin microphones into. I'm starting this hobby on the ground floor and I don't have a scope or even a way to connect to my sound card.

Here's the retail product: http://www.workmanelectronics.com/categorycatalog.htm
I was thinking of a project box, with the microphone panel jack and old speaker and a simple circuit. Just wondered if anyone had built one.

Thank you.
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VA7CPC
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Posts: 2406




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« Reply #6 on: October 14, 2012, 08:46:01 PM »

OK -- from the ground floor:

1)  Different mic's have different pinouts.  So the first thing you need is two sockets (4-pin, and 5-pin), and some kind of patch-board that lets you cross-connect the pins on the sockets to their "logical" uses:

. . . Mic +

. . . Mic - (and/or "Ground")

. . . Ground

. . . Push-to-talk

2)  Some mics (e.g. Icom) require a DC bias voltage.   With Icom's, the DC bias voltage is "phantom power", on the "Mic +" line.   For others (I don't know which) it may be on a separate wire.   You need a way of delivering that voltage, and of _blocking_ it from the audio-frequency microphone output.

3)  You need an amplifier, to raise the mic's output voltage to something you can hear (through headphones or loudspeaker).  "Any op-amp" will work.   A Behringer Xenyx 502 mixer will work even better, and cost about 38.   Or you could use any computer soundcard -- the "Mic In" jack goes to a usable mic preamp.  The "ring" contact supplies a reasonable bias voltage, the "tip" contact is for audio-frequency microphone output.

That's what you need for "Does this microphone work?"  testing, on a wide range of microphones.   

If you want to do sensitivity tests, or frequency-response tests, that's a whole other ballgame.

I hope this is less confusing than previous posts . . .

           Charles
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G8JNJ
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« Reply #7 on: October 15, 2012, 08:36:50 AM »

Hi Chris,

Sorry - I should have clarified some points in my earlier posting.

Soundcard Oscilloscope is free software that turns your PC and Soundcard into an audio frequency Oscilloscope, Spectrum Analyser and Signal Generator.

With this software running you have all the components of an audio lab without having to buy any hardware.

Most PC and Laptop soundcards use 3.5mm (1/8th inch) stereo jacks for audio in and out. You only need to makeup a simple adaptor cable to connect between your microphone and soundcard microphone input. It's at least as easy (if not easier) as making up a dedicated test box with a built-in amplifier.

A general note to all readers - If you haven't ever experimented with your PC soundcard connected to your radio - I'd strongly recommend trying it - there is a lot of very good free software available that allow you to do all sorts of amazing stuff.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com
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