I am building something and have a small amp from an old set of computer speakers and I'm trying to hook a small electret microphone to the input of the amp and get it to play through the speaker. I didn't think it would work by just connecting it to the input wires but tried it anyways and of course I got nothing. Is there anything I can do to get this to work? Thanks guys

 

The problem is that the audio amp wants a line-level signal in, and the little mike can't supply it. You need a preamp -- http://www.discovercircuits.com/A/au-preamps.htm.

 

Thanks man

 

I had some free time today and put together this circuit.
http://www.reconnsworld.com/audio_simplepreamp.html

Im a little confused on how to connect this preamp to the speaker amp. The preamp only has 1 output which I would assume would go to the positive on the amp input but what about the negative? Would I just ground that to the battery ground? I went ahead and tried some variations of the wiring and I cant get this microphone to work. All Im getting is some radio station in the back ground. Any advice?

 

The grounds will have to be tied together. That would be the battery negative and the amp negative.

 

Maybe your microphone is not an electret type. Look in Google Images for Electret Microphone.
It must have the preamp compactly built (not on a breadboard) and use shielded audio wire between the mic and the preamp, and from the output of the preamp to the audio amp input.

If the mic hears the speaker then you will have acoustical feedback howling as the sound goes around and around.

 

I still cant get this thing to work correctly. The Mic just is not working. I drew a pic to make sure everything is connected correctly. The only other thing I can think of is I pulled the mic from an old cell phone headset. I know it worked but I kinda guessed that it was an electret mic. Do you guys see anything wrong with this setup??

http://i189.photobucket.com/albums/z173/SilvrEclipse/Circuit-1.jpg?t=1234922231

 

Use 9v and change the caps to 10uf.
Plus side to the mic and plus side to the transistor collector.
But I expect you will need even more power to the amp.

 

Your schematic should work fine if the input impedance of the amp is 10k ohms or more.

 

I'm more concerned with the output cap. Many PC amplifiers expect to see a speaker output - not a line out. Or they did in the old days...say <1993.

 

You forgot to post the schematic or part number of your audio amp. Maybe its input must be connected to 0V with a resistor or to a voltage divider at half the supply voltage.

 

It dont have a schematic or anything for this amp. I just took it out of a set of desktop speakers. The amp works, when I hooked up the microphone I got nothing from it but when I touched the negative wire for the amp input I was pickin up radio stations.

 

Can you provide a good photograph of what you have? The preamp and amp.

 

Yea I will get one when I get home.

 

Ok here are some pics I just snapped. The on the preamp, the top of the board is the +. The bottom is the - and the middle wire is the signal. Im running 12v to the amp and ran another resistor inline with the preamp to knock the voltage down to 8v or so. The mic is on the left of the preamp. I ran the signal from the preamp to the right and left channel of the amp and all the negatives tie together. Power source is not connected right now but everything else is wired up.

http://i189.photobucket.com/albums/z173/SilvrEclipse/DSCF2716.jpg?t=1235753324
http://i189.photobucket.com/albums/z173/SilvrEclipse/DSCF2717.jpg?t=1235753383
http://i189.photobucket.com/albums/z173/SilvrEclipse/DSCF2718.jpg?t=1235753411

 

Im running 12v to the amp and ran another resistor inline with the preamp to knock the voltage down to 8v or so.

Then you knocked down its gain from 180 to almost nothing.
You should use a voltage regulator, not a resistor.

Get rid of the extra resistor and add a 9V battery with a 100uF capacitor to power the mic before you make a voltage regulator.

 

Ok I will give that a try. Hopfully it will fix it.

 

Thanks AudioGuru, the mic works now. I didn't add the 100uF cap yet, what exactly is it going to do?

 

Thanks AudioGuru, the mic works now. I didn't add the 100uF cap yet, what exactly is it going to do?

As the battery runs down, its internal resistance rises which causes its voltage to swing up and down with the audio that causes positive feedback.
Then the output will make a motor-boat sound: "putt, putt, putt etc".
The 100uF capacitor smooths the voltage from the battery so it does not jump up and down.

 

The mic is working great now. I went ahead and put the 100uF cap on it earlier. It seemed to take some of the interference out of the circuit. I am getting a much cleaner signal now. I went ahead and added a 5v regulator to the preamp also. The whole thing will run off a 12v power source now.

Only issue is the volume is a little low. Is there anyway to make it louder? It may be fine for what Im using it for but I have to keep the volume on the amp all the way up.

Thanks again guys