A fully analog, low-cost, three-phase power supply is built. It is based in an op amp phase-shift oscillator plus three power stages. The latter are three push-pull stages inside a feedback loop which determines the voltage gain. This circuit was proven to work remarkably well for classroom demonstrations of three-phase electric power. This configuration also illustrates the advantages introduced by negative feedback: the voltage gain stabilization and the reduction of non-linear (crossover) distortion, as well as the use of a source degeneration configuration which improves thermal stability.