On Angel’s Wings, Part 1 - A Speaker Design for the Bohlender Graebener RD-75 Planar Magnetic Driver

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.

This article continues the classic JFETs series of articles by Erno Borbely and introduces one of his starter kits with an all-JFET line amp. Originally published in audioXpress March 2005 this is an essential reading to understand the “building blocks” of the “Borbely amplifiers”.

The basic circuits on which Erno Borbely based most of his projects are described in “JFETs: The New Frontiers, Part I and II,” published in Audio Electronics AE 5/99 and 6/99, and “All-FET Line Amp,” published in audioXpress May 2002. As the author admits, these were the “building blocks” on which many - if not all - of his amplifiers are based. This articles continues his JFETs series and was originally published in Audio Electronics, Vol 5 1999.

The basic circuits on which Erno Borbely based most of his projects are described in “JFETs: The New Frontiers, Part I and II,” published in Audio Electronics AE 5/99 and 6/99. Referring to these articles frequently, the author admits, these were the “building blocks” on which many - if not all - of his amplifiers are based. This article is the first part, as originally published in Audio Electronics, Vol. 5 1999.

Introduced in 1948, the Fender Champ single-ended 5 W guitar amplifier is “the” classic tube practice amplifier and it has been remade a few times over. In 1992, Kirk Elliott shared his take on the design, transforming the stock Champ into a quieter, safer, and more reliable studio amplifier. This article was originally published in Glass Audio Volume 4, Number 2, 1992.

A great solid-state project where National Semiconductor’s (since 2011, a part of Texas Instruments) LM4702 meets up with Renesas lateral MOSFETs, this article by Jack Walton was originally published in audioXpress July 2007 and it is still cited as a reference today. An ideal project for the DIY enthusiasts.

With little time to present a project for the annual Burning Amp Festival (BAF) in San Francisco, CA, Michael Rothacher decided to do a preamplifier project using static induction transistors (SITs). He wanted a versatile preamplifier that would work well in a variety of situations, and which could fit conveniently in a suitcase. This article was originally published in audioXpress, April 2014.

Bruce Brown explains his successful method of rebuilding a vintage W-7 tube amplifier from Heathkit. As the first power amplifier that broke $1 per watt barrier of listening power, the Heathkit W-7 was a major breakthrough for audiophiles. Introduced in 1958, it carried a list price of $54.95. This article was originally published in audioXpress, May 2007.

Here is a simple portable device from George Ntanavaras that can help answer the question about peak voltage and peak current requirements and whether or not your power amplifier is capable of driving your loudspeaker without clipping. This article was originally published in audioXpress March 2015 — Focus on Test & Measurement Edition. (Updated Dec 2015)