A Portable Tube Preamp

In this amazing project by Gregory L. Charvat, two pre-amplifiers are used with a battery powered high voltage supply. The high voltage supply works by creating a square wave with a 555 timer. The square wave is fed into a small audio power op-amp. The output of this op-amp is back-fed into the secondary of an audio output transformer, generating high voltage AC 170V at 40 kHz. This signal is rectified, filtered, and regulated in a conventional sense. The entire system runs on 8 AA batteries and should operate for approximately 4 hours continuously. This article was originally published in audioXpress, March 2010.

Keeping things small and inexpensive — and at the beginner’s level — Rick Spencer shows you how to build your own single-ended amp. For about $10 worth of tubes and some small transformers, you can build this neat little amp in one weekend. This article was originally published in audioXpress, April 2004.

In this classical tube amplifier project, author Bob McIntyre offers what is effectively the foundation for many designs that we can find currently in the market. This is not surprising. The Mighty Mouse is indeed a good sounding and inexpensive project that is also a good introduction to tube amplification. This article was originally published in audioXpress, April 2006.

This Class A tube headphone amp project, which the author created for Vintage Audio, includes a 6SL7GT for the input stage and a 6AS7G for the driver, and is able to drive headphones with impedance at or above 64Ω. The article provides a full description of design fundamentals and some useful guidance on the construction process. The result, as the author describes, should be “a satisfying headphone amp that will provide years of enjoyment.” This article was originally published in audioXpress, June 2008.

In 2008, Nelson Pass submitted an article on its new F5 power amplifier design to audioXpress. At the time, he wrote: “I feel that it’s important to support AudioXpress, a magazine with which I have a 35 year history, and which also serves as a mainstay for the DIY community. Lately they have kindly printed projects that I had already posted on the web, but I decided that they deserve a little better than that.” Effectively, the F5 project was published in May 2008 and had a huge impact on the global DIY community and certainly contributed for the fact that audioXpress is still around today.

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.

Here’s the final section in our series on parts reliability, how to choose them and how to estimate their life expectancy. In the third part of this article, the author continues to examine electronic components, and discusses what we can do about reliability. This article series was published in audioXpress, from November 2001 to January 2002.

Everything you need to know about how parts function, and how to select and maintain them. In the second part of this article, the author continues to examine electronic circuits with a look at some common circuit components, like resistors, semiconductors, diodes, small signal transistors, power Semiconductors, and microelectronics. This article series was published in audioXpress, from November 2001 to January 2002.

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.

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.