Tiny Mic Preamplifier

Rajkumar Sharma      http://www.rajkumarsharma.com  
8532
Project tested

A017

The Tiny Mic Preamplifier based is based on a single transistor amplifier design.  It amplifies the output of the electret condenser microphone.  Good choice for Karaoke.

Specifications

  • Power supply: 5 ~ 9 VDC @ 2 mA
  • Provides standard audio signal
  • PCB dimensions 26 mm x 56 mm

Schematic

SCH

Parts List

BOM

PCB

3 Response on “Tiny Mic Preamplifier

  1. The voltage gain of only 32.5 is much too low for a mic preamp. It should be 150 to 200. The gain is low because the low input impedance of the transistor loads down the high output impedance of the mic.
    The polarity of C1 is backwards. R4 and R5 are not needed.
    The transistor is biased wrong since it is almost saturated and loud sounds will cause clipping.

  2. Assuming the mic capsule has a preamp already, C5 and R4 are unnecessary. Reverse C4 and change R5 to 56K, this stabilises the bias point for maximum output voltage. No need to have R3 going to collector, put is on V+. There is enough NFB via the 56R emitter resistor, this theoretically gives a gain of 100X but will be more like 60X in practice. If the capsule does not include a preamp, the circuit is unable to be used as a condenser microphone preamp.

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