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With this Instructable we are going to connect a karaoke type mic to a powered speaker for singing mainly.
I had an old powered speaker the kind with base box and the 2 other speakers separate from the base and an old mic from a karaoke player.
So i decided to connect the mic direct to the speaker, with a pre-amp in between.
After much searching i decided to try this circuit in the picture. For one reason it is able to input both types of mic's. Electric the little ones you find in headset's and Dynamic the bigger ones that will work with a karaoke. Another reason it is simple and uses few parts. Stuff i already have. 

Given it's simplicity this thing actually works quite well. The first mic i tried was an electric mic. You can see it in the pictures. It was from a broken computer headset. Worked but not great, acted sort of like a boom mic. The kind used in private airplanes and much feedback.
The second one i tried was from a broken karaoke player. WOW i powered everything up and it worked great, sounded great with no feedback. Worked like a P-A system should.
With that i removed any components not needed in the pre-amp. Basically the electric mic parts. Consisted of one resistor and two capacitors. That was not the best design decision. It will work like this, but those parts are need to be in there for best performance. So i re-installed the 2 caps and the resistor. Now its back to great.

 This can be seen in action by clicking the video link below.

YouTube Video 1

Step 1: Mono to Stereo

The pre-amp was only a single output. Sense the speaker has a left and right input i added this " splitter " circuit. Mono in and Left - Right out. Stereo i suppose you call it or two chanel.
Not really sure how much better it actually sounds with this installed, but in my mind it sounds better so we will just go with that.  
It can be used in either direction. Stereo to mono or mono to stereo.

Step 2: Bread Boarded Circuit

The boarded circuit.
In the end i did't use the volume control at the pre-amp.  
I just relied on the main speaker volume. 

Very few components for what it does. 7 components including the LED. Mine actually has eight. I used two 100K resistors instead of the 220K it calls for.

            BOM: 

RESISTORS

  • 1)  4K7 ohm
  • 1) 220k ohm
  • 1) 2k2 ohm
  • 1) 120 ohm
  • 3) 600 ohm
CAPACITORS:
  • 4) 10uF
  • 1) 100uF
 
 TRANSISTOR:

     1) BC547






Step 3: PCB

I mounted the components on perf board, then after testing the sound and volume just wasn't very good.
So after some investigation i found i had gotten the output capacitor in backwards.
After fixing that it was running great.    

Step 4: Non Altoids Tin

An amp like this is best mounted in a tin box to help reduce noise, static. Scene Altoids are not available here i made a crude tin box. Pop riveted it together. Now this box is no where close to winning any beauty prizes. It only needs to be functional, besides it is hidden inside the speaker box out of site.  

Step 5: Install and Get Power

I took power from the amp powering the speakers. It was at 13.v, pretty high. I added 3 1N4001 diodes inline with the pre-amp power line to bring the voltage down some. That brought it to about 11.2v. Still high scene the circuit was designed for 9v and i was actually running it on 5v on the bread board. I could tell there was still " OVERDRIVE "  even at 11.2v. I am not sure if overdrive is the correct term for this but it sounded good to me, we will go with it. 
I decide i would go ahead and assemble everything and try it. 
It is put together and working as can be seen in the video.              
                                                           

 As soon as i get  irritated enough with the overdrive issue i will go back in and drop the voltage to 5v  

Thanks for looking!
<p>electret input???</p>
what does your electret mic look like?
Hi thanks for looking. <br>In step 2 the very last picture shows the electric mic. Skinny black thing in the bottom of the picture.

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Bio: Why would i buy something ready made when i can make it myself with half the features for twice the money? DIY!
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