DIY SRPP Headphone Amp for Warm Sound

With a circuit configuration known as series regulated push-pull (SRPP), you can build a low-power tube amplifier that doesn't require the infamous output transformer.

With a little know-how and some basic parts, you can design a hybrid amplifier in fairly short order. This project combines the best attributes of both tube and transistor technologies.

Dave Erickson built his first multi-zone audio system in the early 1990s using C microprocessor code he developed on Freescale MC68HC11 microprocessors. In early 2014, he detailed how he upgraded the eight-zone system, which uses microprocessor-controlled analog circuitry.

Looking for a circuit solution to the problem of measuring AC voltage and current using DC meters? Synchronous rectification solves a pesky problem caused by diodes.

Bill Reeve’s article, “Repurposing Antique Radios as Tube Amplifiers,” provides vintage radio resources, simple circuit diagrams, and essential part info. He also covers the topics of external audio mixing and audio switching. The article appeared in the May 2012 edition of audioXpress magazine.

Charles Hansen described a DIY phase meter calibrator using all-pass, phase-shift filters in a November 2006 article published in audioXpress magazine. Being able to measure phase angle is often helpful, so Ron Tipton decided to build the calibrator as described. In Hansen's design, there was a set of five calibrations frequencies: 10 Hz, 100 Hz, 1000 Hz, 10 kHz, and 100 kHz. Hansen relied on an external oscillator to drive the calibrator at these input frequencies. Ron Tipton made some modifications that better suited his needs, described in this article.