A general-purpose preamplifier circuit is useful for boosting low-level sound sources, such as microphones, contact mikes, guitar pickups, and coils, to the line-level signal strength typical of computer audio, flash recorders, etc. After preamplification the signals can be sent to powered speakers, such as those used for computers or phones, or mixed with line-level sources using simple, passive mixers. The guitar is always the best instrument for evaluating distortion. As the gain increases, the sound shifts from clean amplification through tube-like “overdrive” into distortion and, eventually, uncontrollable noise and oscillation. Preamplifier and distortion circuits are very useful in their own right. And if one can successfully boost ordinary analog audio to the near-square wave signals put out by more extreme distortion circuits, the door to some unusual signal processing is opened.