A Single-Ended 6550 Amplifier

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.

Three audio experts discuss the role of distortion levels in what we hear. The debate was caused by an article titled “Amplifier Musicality - A Study of Amplifier Harmonic Distortion Spectrum Analysis” by Jean Hiraga, which originated comments by Jan Didden, Dennis Colin and a subsequent response by Jean Hiraga. The original article appeared in audioXpress March 2004 and the resulting conversation was published in audioXpress October 2005.

The upcoming AES 59th International Conference, on Sound Reinforcement Engineering and Technology, will feature a special workshop hosted by Flex Acoustics and will include a demonstration of Flex Acoustics' inflatable membrane low-frequency absorbers, showing the overall effectiveness of their innovative acoustic absorption at low frequencies.

Radial Engineering confirmed the updated version of its long awaited Space Heater is now shipping. The Space Heater is an eight channel tube summing mixer with high voltage tube overdrive, featuring individual input and output control for all eight channels, which took a year to perfect since first announced in 2014.

Promised to start shipping in June, Alo Audio’s new Continental dual mono headphone amp with USB DAC was already the talk of the show at the Headphonium section of The Show Newport. Alo Audio will not be alone with the idea of designing an hybrid tube/solid-state “transportable” headphone amp and USB DAC but it certainly did it with an interesting design.