JBL L300 Modification

In this much sought after modification project, Nelson Pass rekindles his desire for the JBL L300 Summit loudspeakers and completes a renovation. As he explains, “it is not a trivial task to improve on original JBL design." "I think I’ve managed to respect the JBL legacy while tweaking the sound to reflect the tastes of the 21st century.” Article originally published in audioXpress, January 2012.

In this article, originally published in audioXpress, February 2004, the author describes how to achieve low distortion from power triodes. As he explains, his preamp is “a little different from most, using low-mu power triodes to get good performance with only one amplifier stage, and no negative feedback. This achieves the modest gain required along with very low output impedance.”

Attention, all first-time (or wanna be) builders of single ended directly heated triode amps. This project’s for you. This is an easy to build, simple direct-coupled input/driver circuit that provides the proper drive voltage to the grid of the 211. A nice way to experiment with a single-ended (SE) triode amplifier.

Here’s a long-forgotten, but still high-quality, power amp design that’s easy to build, requiring no esoteric tubes or parts. Originally published by audioXpress on May, 2003, this project was submitted by Helmut Otte, who worked at the University Of Applied Sciences Hamburg, after having started is electronics career at Philips Service department in Germany.

Here’s a do-it-yourselfer’s dream in tube amp design: four operating modes, high quality, low cost, and low distortion. An article originally published by audioXpress in May 2007. A true versatile project which we think deserves to be shared.

Tube life can be extended if you delay the application of high voltage until after the heaters have warmed up and current can flow. This little module does just that: depending on the setting of a jumper, it delays the high-voltage for 40 or 60 seconds after the amplifier is switched on. And the module is available as a kit. This article was originally published in audioXpress, February 2014.

This project, originally published by audioXpress in December 2011, has been the topic of much discussion, updates and follow-up projects, so much so that we decided to make it available online. As the author, Robert Nance Dee, explains, “…the people who have listened to this amp can hear the difference. I built it as a companion to my 5002 power amp, both using the HA5002 buffer.”

This circuit contains an audio amplifier capable of driving a speaker with circuitry that automatically maintains the same relative maximum output regardless of extreme levels that are occurring at the input. It does not “compress” the peaks, but simply “turns down the volume” as you would do with your volume control

In this very popular article published by audioXpress in March 2004, Jim Hagerman explains the design theory behind this popular low-cost DIY kit. The FryKleaner was designed to be a complete self-contained burn-in system. Included on the deceptively small circuit board is a very sophisticated waveform generator and built-in power amplifiers capable of directly driving cables. A wall-wart supplies power.

This article by Doug Ford describes a design for a (relatively) simple passive-matrix surround-sound decoder and the interesting things discovered by the author during the process. The decoder features an analog time delay, implemented with several cascaded all-pass networks and it improves sound system quality by eliminating out-of-phase information.