A Solid-State Single-Ended Power Amp

In this simple amplifier project, Ed Simon describes a Class-A amplifier design that mainly intends to reproduce music with reinforced emotional expression. That's what you normally get with a quality design, but to achieve it, the author shares the complete concept, power requirements, circuit topology, construction and testing of this single-ended amp... in a solid-state design. This article was originally published in audioXpress, April 2006.

I recently purchased a pair of MTX Audio Monitor 5i 5.25″ bookshelf speakers because I needed small monitors for a new computer. I do some audio restoration, so I wanted good sound quality when I wasn’t using headphones. My tests determined that the reviewers were right about the MTX 5i’s weakness in the midrange frequencies. I measured the response and it was not especially flat. This convinced me to update the drivers. This article was originally published in audioXpress, June 2013.

The controversy over subjective versus objective loudspeaker evaluation has raged on for decades. However, to my mind, there is no controversy. These criteria are simply two faces of the same coin. In over 30 years of designing loudspeakers, I have found the following measurements taken as a group provide the strongest predictor of loudspeaker preference available to us today. Want to know more? Read this reference article, originally published in audioXpress, September 2008.

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.

I built this amplifier to run my Dynaudio X12 speakers. The X12s are not known for efficiency, but these little mono blocks run the accurate X12s with ease. Don’t be fooled by their low power output. The limiting factor is voltage, not their ability to drive a load. This article was published originally in audioXpress, February 2012.

November 2013 was the first issue of the redesigned audioXpress in its current form, featuring several new sections, including the first of its R&D Stories series, focusing on engineering and product development - independently of the audio application field. This article by Stuart Yaniger on QSC’s Flexible Amplifier Summing Technology (FAST) was a reference for many to follow.

In this article from audioXpress archives, originally published in July 2003, Charles Hansen describes four hybrid power amps that anyone might consider for their own designs. Starting from the idea that an op amp provides both a differential input stage and high overall gain in one package, Hansen explores the ramifications of using an op amp as a combined input and voltage amplifier stage in power amplifiers. As he writes, “I did not build the four amplifiers shown in this article, but I did run a SPICE simulation to verify that they did perform as audio amplifiers."

This project is based on Erno Borbely’s EB-602/210 single-ended pure Class A amplifier and is capable of driving headphones between 32 and 600Ω. It consists of two identical but separate amps laid out on the same PCB. The schematic is the same as Erno’s extremely popular hybrid tube/MOSFET line amp, published in Glass Audio 1/98. However, the dual triode at the input is replaced by a dual JFET (SK389). This article was originally published in audioXpress, July 2004.

Speed up your crossover prototyping and preserve your crossover components with this true plug-and-play approach. As the author, Ramkumar Ramaswamy explains, today’s computer simulation software allows you to design passive crossovers extremely accurately. “Is there a way to effortlessly and reliably plug and play with a set of (fixed) capacitors across crossover prototypes without the fear of ending up with broken leads? This question drove me to design this passive crossover prototyping system”, he explains. This article was originally published in audioXpress, March 2007.

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.