common emitter preamplifier problem

Question

i need an amplifier to amplify my electrolyte microphone sound and put output to sim800l . currently i just experiment with amplifiers to find good gain for sim800l mic input.

some one advise me to use common emitter as pre amplifier . so i found this circuit on the internet and check the simulation in Proteus 8 software.

in theory this circuit work great .i add electrolyte microphone to input of circuit in reality. i just can hear very weak audio in output but without amplifier and just connecting electrolyte microphone to sim800l sound is much better.

edited: i want to know why i cant amplify my voice in real circuit . i check all wire connection and its not wire problem

Answer 1

Your amplifier has low input impedance (resistance). If collector current is 0.5 milliamp, your transistor base looks like (52_ohms * beta) ~~~ 5,000 ohms.

The biasing is a GOOD approach, but I'd cut that resistor in half, and insert a large capacitor from the midpoint to ground. That way, the needed DC biasing still occurs, yet your amplifier gives you maximum gain.

I'd raise the V_collector, by using 470,000 or 680,000 or 1,000,000 ohms from collector to base. And as I suggested, cut that into 2 resistors and bypass the midpoint to ground; use a large cap, or else your bass frequencies will br missing.

Depending on the value of the load (not just a scope), you may want a 2nd transistor to provide high load currents while letting your first transistor continue to provide maximum gain. Have the transistor: collector to VCC, base to first transistor output, emitter to 1,000 or 3,300 ohm to ground. Do not short this output (the emitter) unless you add 47 ohms into the collector.

If you operate this circuit on +12volt (collector approximately +6v), your gain should be 6v/0.026v === 240X. An electret microphone may have such large Vout that your preamp goes into distortion. In that case, add 100 or 270 ohms in the emitter.