For the testing of components, on the bench, the presence of an amplifier that provides pure signal with a few hundred milliwatts of power is indispensable. The amplifier we present has excellent sound quality, as it uses transistors with complementary symmetry output, and in addition it has great sensitivity for testing stages that have low intensity signals. The hobbyist will be able to use this amplifier in the proof of microphones, phonographic capsules, as a signal follower, in the proof of loudspeakers (which will be connected at its output), headphones, etc. Four general purpose transistors are used in this amplifier, which will perform best with a 9 V power supply (also works with 6 V). NPN transistors can be BC548 or equivalent, such as BC238, BC547 and BC237. The PNP of the exit stage can be the BC328 and the NPN of the exit the BC338. The diodes are BA314 and all 1 / 8W resistors. The P1 potentiometer can be 22 k or 47 k with a switch, and the electrolytic capacitors for 12 V or more. When assembling, short connections must be made and the entry, if made with long wire, must have shielded wire.
