This portable mic preamp circuits uses only two transistors as an amplifier. In addition, the mic preamp circuits requires a very low supply current, only just 2mA.
Because the current absorbed mic preamp circuit is very small, then the battery will long lasting for used. If using battery 9VDC, usage estimates will long life up to 3 months.
Mic preamp circuits has harmonic distortion of 0.1% for all of the frequency response. The maximum permissible input voltage is between 25 mV to 200 mV.
Basically this mic preamp circuits produces low noise, high gain and strengthening two stage by the transistor. Resistor R6 serves as a negative feedback to stabilize the circuit performance.
Potentiometer P1 is used to set the gain in accordance with the desired output. The first stage transistor using a PNP-type, while the second stage uses an NPN. Both transistors have been combined perfectly.
Portable Mic Preamp Circuits Parts List:
R1,R2,R3 = 100K
R4 = 8K2
R5 = 68R
R6 = 6K8
R7,R8 = 1K
R9 = 150R
P1 = 2K2 Linear Potentiometer
C1 = 1 µF/6.3V polyester
C2,C3,C4 = 100 µF/25V elco
C5 = 22 µF/25V elco
Q1 = BC560C
Q2 = BC550C
J1 = Jack socket (Mono 3 or 6 mm.)