This simple preamplifier with two transistors may be used in a wide range of applications. The transistors may be the BC548 or equivalent, and the circuit has low power consumption. Power can come from battery or supply as consumption is very low. The 100k resistor can be changed as the signal source characteristics in order to achieve better performance. The circuit has average input impedance and an output impedance of about 4k Ω. The level of the output signal is a few hundred millivolts, enough to excite the input of most common amplifiers. The same circuit can be mounted with PNP transistors, such as BC558, simply by inverting the polarity of the power supply and electrolytic capacitors.
