Audio-Optical Isolation Amp

When we connect audio components, interference may occur from various power and signal grounds. This circuit enables the full galvanic isolation of sound frequency signals with optical transmission in excellent quality, eliminating interference. This article was originally published in audioXpress October 2004.

This design by Joseph Norwood Still is a control unit that the author described as offering “lifelike concert-hall performance for a modest cost”. A great tube-based amplifier for phono and line sources, featuring a very subtle bass enhancement control using negative feedback to enhance only selected frequencies, below 400Hz. As the author described, a great project for discriminating audiophiles.

Inspired by debates on the Internet about quarter wave designs with Tang Band 3˝ full-range drivers, the author decided to design its own quarter wave loudspeakers. This article was published in audioXpress, March 2007 and the results were simply spectacular, generating worldwide interest. Recently, Bjorn Johannesen created a successful business with his own speaker company, called KVART & BØLGE, which means Quarter & Wave in Norwegian and Danish.

Ron Tipton explains how he built his sound level meter and spectrum analyzer, the Model 527, around a Velleman Audio Analyzer kit (K8098). This is a barebones kit with no enclosure or power supply, but for the price, it is very versatile. Originally published in audioxpress, December 2013.

Here’s a simple, safe, inexpensive project for beginners and those who wish to “try tubes.” Meanwhile the project has been tried, tested, approved and improved, become one of the classic DIY audio projects from the author. This article was originally published in audioXpress magazine, November 2002.

In this much sought after modification project, Nelson Pass rekindles his desire for the JBL L300 Summit loudspeakers and completes a renovation. As he explains, “it is not a trivial task to improve on original JBL design." "I think I’ve managed to respect the JBL legacy while tweaking the sound to reflect the tastes of the 21st century.” Article originally published in audioXpress, January 2012.

In this article, originally published in audioXpress, February 2004, the author describes how to achieve low distortion from power triodes. As he explains, his preamp is “a little different from most, using low-mu power triodes to get good performance with only one amplifier stage, and no negative feedback. This achieves the modest gain required along with very low output impedance.”

Attention, all first-time (or wanna be) builders of single ended directly heated triode amps. This project’s for you. This is an easy to build, simple direct-coupled input/driver circuit that provides the proper drive voltage to the grid of the 211. A nice way to experiment with a single-ended (SE) triode amplifier.

Here’s a long-forgotten, but still high-quality, power amp design that’s easy to build, requiring no esoteric tubes or parts. Originally published by audioXpress on May, 2003, this project was submitted by Helmut Otte, who worked at the University Of Applied Sciences Hamburg, after having started is electronics career at Philips Service department in Germany.

Here’s a do-it-yourselfer’s dream in tube amp design: four operating modes, high quality, low cost, and low distortion. An article originally published by audioXpress in May 2007. A true versatile project which we think deserves to be shared.