Arduino-Based Tube Power Amplifier Controller

In a nod to the Maker Movement, this project uses a common open-source microcontroller module, the Arduino, to build an automatic power controller for a tube power amplifier. The resulting controller is very simple — a $25 Arduino module, a couple of dual op-amps, a few other components, and a 5-VDC power supply plus some opto-isolated switches. This article was originally published in audioXpress, February 2015.

In 2014, audioXpress invited Scott Dorsey to update his popular reamping project that modeled the source impedances of a couple typical guitar pickups. He wrote the original article more than a decade ago for Recording magazine. In “Reamplification Revisited,” Scott brought us an updated version of his Kludge reamplifier box with added detail. This article was published in audioXpress, January 2015.

Following the publication of the original Hideaway TL Sub project in audioXpress July 2006, Bjørn Johannesen submitted a follow-up of its “invisible” subwoofer project, using a new updated driver - a Peerless 10˝ SLS 830668 woofer - and a slimmer profile to fit under its new couch, with only 15cm of free space. The article was originally published in audioXpress, October 2007.

This article, a Danish blueprint for an “invisible” subwoofer was originally published in audioXpress July 2006 and it is the first of two by Bjorn Johannesen. In this first article, the author describes a successful transmission line to replace a vented sub, inspired by Rick Schultz articles. A project where the first approach revealed a resonance frequency lower than expected — lower than the driver’s Fs, leading him to study Martin J. King’s quarter wave design.

Here is an excellent beginner’s project for those just getting started in this hobby. This “little” amp is easy to construct and has only about 25 parts in each channel. The system transformers are very inexpensive, and the total cost involved for a complete stereo version should be very minimal! This article was originally published in audioXpress, December 2001.

Many of today’s receivers and preamplifier processors do not have phonograph inputs, so anyone with a vinyl collection will need an external phono preamplifier. Bill Christie decided to build one using a TI high-performance op-amp, since the data sheet already included the schematic for a phono preamplifier. This article was originally published in audioXpress, July 2013.

TERESA amplifier is a simple and cascadable Class-AB design. The name is an acronym for manufacturers TExas Instruments and REneSAs, who provided the parts for the core of this amplifier. The result is worth seeing and hearing! This DIY project does not require any special experience in detailed analog circuit technology to build. This article was originally published in audioXpress, November 2014.

In January and February 2001, audioXPress included a project from Thomas Perazella, describing in detail the design and construction of a speaker using the Bohlender Graebener RD-75 planar magnetic driver. This is the second part of the project, detailing the final part of the speaker construction, measurements and listening trials.

In January 2001, the first audioXPress magazine issue (Vol. 32 No.1) included this project from Thomas Perazella. Published in two parts, the articles described in detail the design and construction of a speaker using the Bohlender Graebener RD-75 planar magnetic driver, including references to previous experiments with dipole baffles. This is the first part of the project.

Stuart Yaniger wrote a great article for audioXpress in February 2009, The ImPasse Preamplifier, describing a tube preamp to drive a pair of Nelson Pass’ First Watt F4’s (or other low-to-unity-gain power amplifiers) in balanced mono. Yaniger’s preamp is truly an elegant design with very, very low distortion, using a 6SN7 to drive a 6922 in balanced mode. There are LED’s, NE2H neon lamps and depletion MOSFETs in the design.