This preamplifier - quite simple - can work to drive common amplifiers with the signal of microphones of various types or capsules.
We use only one transistor to amplify the signal, in this elementary configuration powered by only 6 volt. If you use an improvised microphone, from a speaker, and you do not get enough driving from the amplifier, with this step things get much better. (Figure 1)
The transistor can be either a commonly used NPN like the BC548, and the capacitors are ceramic.
In order to avoid buzzing, the input and output cables must be shielded with the mesh connected to the negative of the source.
If there is a tendency for distortion, R2 can be changed in the range of 2k2 to 22k, in order to obtain the best performance.
The output must be connected to the amplifier input (AUX). In the assembly (Figure 2), observe the polarity of the batteries. In fact, the power can be made with voltages between 6 and 12 volt, without need of modifications of values of components.
MATERIAL LIST
Q1 - BC548 or equivalent - general purpose NPN transistor
C1, C2 - 100 nF (104) - ceramic capacitors
R1 - 1 M x 1/8 W - resistor (brown, black, green)
R2 - 10k x 1/8 W - resistor (brown, black, orange)
S1 - single switch
B1 - 6 V - 4 small batteries
Miscellaneous:
Terminal strip, jacks and plugs, support for 4 batteries, shielded wires, wires, welding, etc.
