A Simple LED Bias Meter and Supply for the Dynaco ST70 and Other Tube Amplifiers

Recently, I got bitten by the nostalgia bug and picked up a pair of old factory-wired Dynaco ST70s in pretty nice condition. On one of the Dynaco ST70s, I installed a new 6GH8 driver board instead of dealing with the rare 7199 issue, and I designed a small (3” × 3”) PCB to combine the bias supply and added the LED bias-setting circuit. This article was originally published in audioXpress, April 2013.

This Test Bench focuses on a new and extremely clever variable Bl 12″ diameter guitar speaker from Eminence — the 12″ Maverick, from the Eminence Patriot series, which uses their new FDM technology (Flux Density Modulation) to allow some really desirable distortion characteristics that have become the signature of blues and rock guitar playing. This article was originally published in Voice Coil, January 2011.

It’s very questionable that anyone would still be on the market for another USB 2.0 compact audio recording interface, given the market saturation and the transition to faster and lower-latency USB 3, Thunderbolt or even Ethernet alternatives already in the market. British company Audient believes there is still a chance and released the iD4, a single-channel unit featuring the company’s Class-A mic pre technology and good quality AD/DA converters for just $199.

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.

Many articles have appeared regarding projects using one of the most sturdy, versatile, and trustworthy audio tubes ever made — the 6550. Most of them show these audio beauties used in the push-pull configuration in order to obtain the greatest efficiency and the most power output. In this article, the 6550 is used in a clean, sweet-sounding, single-ended design. The amplifier has very few parts, is easy to build and repair, and the cost of the project is nominal when you consider the kind of sound that is produced. This article was originally published in audioXPress, September 2001.

During InfoComm 2016, Allen & Heath has released a major firmware update for its dLive series, which includes Director software to enable offline editing and live mixing on a PC with or without a Surface, plus preamp modeling on all 128 channels, 5.1 surround sound, and dedicated Mute Groups. The announcement follows the recent introduction of a host of major enhancements to the feature set and ecosystem of its Qu Series of compact digital mixers.

60 years later, legacy brands Hafler and Dynaco, two of the most prestigious brands of all-time, have come together under the umbrella of Radial Engineering Ltd, Hafler’s former Canadian distributor - turned manufacturer. Since acquiring the brands in earlier 2014, Radial Engineering has been working on new Hafler designs and will now show the first Dynaco products at the High-End Show in Munich.

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.

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.

Cakewalk announced its latest SONAR “Gloucester” release introduces support for Microsoft’s new Windows 10 operating system plus numerous enhancements and fixes. The company is also offering a free demo or Rapture Pro, Cakewalk’s latest virtual instrument for Mac and Windows.