I use Google Translator so there may be errors in the text. I have a problem with connecting a dynamic (not electret) microphone. Dynamic microphones have too low resistance (this one has 200 ohms) and when connected to a smartphone, they work but very quietly. As you know, in a smartphone there is a voltage of about 2.2v at the microphone input (4-pin jack) to power the electret microphone. I would like to use this voltage to build a very simple amplifier with one transistor that would allow me to connect a dynamic microphone instead of an electret one. There will probably be questions about why I want to connect a dynamic microphone. This is absolutely necessary because the microphone has to work in a very noisy environment (moto paraglider). To be precise, it is a dynamic differential microphone (but that doesn't matter anymore) and only such microphones can work in extremely noisy environments. Generally, I mean a system that does not require external power supply and only draws power from the smartphone's microphone socket (2.2v).

Dynamic mic.

I tried to make an amplifier according to this diagram but it doesn't work :(

enter image description here

  • \$\begingroup\$ Can you be more specific than "it doesn't work"? Your circuit looks OK for a first attempt. \$\endgroup\$
    – Jens
    Commented Apr 2 at 23:21
  • \$\begingroup\$ Dynamic mics should generally give larger amplitudes than an electret. Are you sure you connected it correctly without an amplifier? How did you connect it? \$\endgroup\$
    – Justme
    Commented Apr 3 at 4:40

1 Answer 1


Sorry. I had a broken transistor. Everything works. I checked several transistors, 2n2222, BC547, etc. You can probably use any NPN transistor and it will work. Instead of a resistor, I used a 1 megaohm potentiometer and it works at almost every setting except 0 ohm.


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