microphone/output project

Discussion in 'The Projects Forum' started by Mathematics!, Jan 1, 2009.

1. Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Ok I have a PC-Board Condenser Microphone Element part 270-090 radioshack.

I have an old speaker that say's it is an 8 ohm , 2 Watt

The microphone electrical characteristics is
supply voltage 1 to 10 VDC
nominal suppy 4.5 VDC
Current drain 0.3mA (max)
signal/noise 60db (min)
sensitivity -64 +- 2db
Output Impedance 1k ohm.

How can I make it so when you talk into the microphone you here it out of a speaker .

I know P = 2 watts = VI = V^2/R => V = 4vdc => I = 0.5 amp
This means the speaker needs 4 volts and 0.5 amps of current to it.

I am unsure what I need to do to get the microphones out put in the range for the speaker.

I have a 9 volt battery and 1.2 volt battery.
Lots of resistors and capacitors.
Lots of different gage copper wire.
And some transistors I think both PNP and NPN.

For the microphone I am unsure what defineds how much current and voltage it will out put. Is say's that current drained is 0.3mA and output impedance is resistance + i reactance since it is real the impedance must be just 1k ohm resistance.

I know that humans hear in the 20 hertz to 20k hertz range.
So I am assuming I have to use some kind of capacitor , inductor setup.
To alternate the current back and forth and have the microphone effect the frequency in the hearing range to the speaker.

Sorry I am a little lost.
I know alot of different things but I am having trouble in determining what is important current, voltage , or frequency of ossilation ...etc etc

2. Wendy Moderator

Mar 24, 2008
20,735
2,499
Do you want a prebuilt amp, or are you wanting to build one yourself?

3. Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
I want to buid this from scratch.

Just want to be able to talk into the mic and hear it out the speaker.

4. Audioguru New Member

Dec 20, 2007
9,411
895
The microphone is an electret one not a condenser one. RadioShack don't have a clue about electronic parts.
Its output level is about 5mV to 10mV into a high input impedance amplifier.
A speaker needs to be driven from a power amplifier.
If the microphone can hear the speaker then the sound goes around and around making acousic feedback howling and squealing.

An LM386 is a little power amplifier that can drive an 8 ohm speaker to 0.45W at clipping when the 9V battery is brand new. A cheap little clock radio will be louder. You can make your own LM386 amplifier with 4 transistors and many resistors, capacitors and diodes.
The LM386 can be set for a gain of 200 then its output will be fine if you talk loudly and closely to the microphone. An added transistor can amplify it more.

Apr 20, 2004
15,815
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6. Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Well I don't have some of the parts given in the preamp digram but I do
have an op-amp from radio shack. Could I use an op-amp in place of the preamp digram.

I think the op-amp was a LM386 but I cann't find the package that I had it's characteristics.