A compendium of useful audio amplifier circuits for the experimenting constructor

Although the power amplifiers described last month have a respectable amount of gain, some signals may be too weak to produce an adequate loudspeaker output without additional amplification. They can also be further weakened by an excessive mismatch between the signal source and the amplifier. Tone controls are usually required when music is being reproduced, and restricting the bandwidth will clarify speech signals, especially under noisy conditions. Covered in this article are these three issues:

• Pre-amplification
• Impedance matching
• Tailoring the frequency response