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I want to build a Mic Amplifier

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New Member
Hi everybody!
I wanted to build a stereo microphone amplifier to turn my Nokia 5510 into a small audio recorder.
So, what i needed was a microphone amplifier, small voltage battery operated (i would prefer those small coin batteries), with stereo output (for the stereo audio input in the phone) but i don't know how to do do it, not even what components to use. :wink:
Here goes a small list to make it clear:
  • :arrow: Use a low voltage battery
    :arrow: Have a stereo output to connect to the stereo input of the phone
    :arrow: (optional but inportant) Have a small form factor (about 3cmX1cm)
Any ideas?
And then, please tell me:
  • :arrow: What type of microphone to use
    :arrow: What are the components
    :arrow: Wow do i put all that together! :D (the scheme!)
Thanks, all!


Active Member
Look at this circuit:

The first transistor Q1 forms mic. amplifier stage. Use this circuit upto C2 for your purpose. You can use 3V battery in this circuit. The only thing is the gain of amplifier will be less.

I have never seen mobile phone socket for stereo input. Veriy it whether its mono or stereo. It should be mono.


New Member
First, let me thank you for the help.
I just have a question, i use up to C2, so i won't use C2? if so, i have mono input, right?
If not so, i get 3 wires, one is ground, and the other two, what are they?
Oh, and 3v? It's great! as the gain, i don't know how much i will need, becaus this input is used to connect speaker/line out from any sound card, or other audio device to input audio to the MP3 recorder of the mobile.

As for the stereo input, this is not the standard "Hand's-free" kit microphone. This is an other audio input, because Nokia 5510 is also an MP3 player that accepts audio in MP3 format from the USB cable, but also suport's analog audio input trough the ADE-2 cable. Here's a picture of it!
I don't know how much you are familiarized with this equipment, but in a short resume, this is a mobile phone with built in MP3 player and FM radio tunner, so it is an 3330 with 3 more connectors: one for stereo audio input, one stereo audio output for headsets (also used for any hand's-free kit, or to conect speakers with a converter cable thata converts from the 1,5mm stereo jack to the normal 3mm stereo jack(sorry if the measures are wrong, i have no ruller here with me... :wink:)), and finaly one mini USB connector. As ofcourse, the original headset microphone is a 1,5mm jack with 4 connectors, the same from 3210 and 33x0.
So, i think that converting the mono signal to a stereo signal (i'm not worried about channel spliting, i just want to hear the same sound in both channels), would increase the sound quality and turn easier the listening.
Finaly, once again, my gratefulness.


Active Member
You have to use C2 in order not to change the dc bias of the further processing stages (mobile phone's circuit in this case) since capacitor blocks DC signals. TO make this mono amp. into stereo you can use 2 capacitors in parallel in place of one C2. Thus the circuit will have two DC isolated outputs one for each channel. You cannot turn mic signal into a real stereo (channels separated by small delay) with this circuit. It will just produce 2 signals having same information.


New Member
:idea: Thanks! that's a great idea!
I was thinking in building an parallel circuit, but for what i need, it would be stupid! (including in other aspects...:lol:)
Well, i'll try it out this weekend, and then, i'll post here the results! :wink:
Once again, thank you!
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