All items written by Gerhard Haas
PPP HiFi Valve Power Amplifier
May 1, 2001 by Gerhard Haas

PPP HiFi Valve Power Amplifier

Thanks to their pleasant sound, valve-type power amplifiers continue to enjoy uninterrupted popularity. With such an amplifier, you can eliminate the impression of coldness, sterility and artificiality that many people experience with CDs.The design for a power amplifier that is presented in this article is based on the PPP principle. PPP stands for ‘Parallel Push-Pull’. ‘Push-pull’ means that the output stage is composed of two active elements acting in phase opposition. One of the valves handles the positive half-cycles, while the other one handles the negative half-cycles. In a Parallel Push-Pull configuration, the valves in the output stage are connected in parallel with respect to the ac signal. The disadvantage is that the power efficiency per valve pair is less than with classical Class AB push-pull operation. Otherwise the PPP principle has only advantages. This output stage configuration was invented in the early 1950s, and it was the configuration of choice in studios. Reduced distortion, good sound and a wide frequency response were more important in this application area than high power efficiency. With the triumphal march of semiconductor technology, PPP was unable to retain any significant territory, due to its relatively low power efficiency and relatively high price. However, with the aid of modern resources it is possible to construct excellent HiFi PPP power amplifiers at an acceptable price.