You Can DIY! Type 3 Mu Stage Breakthrough

The original Mu Stage project, published in Glass Audio in 1993, remains a popular build, serving the author's purpose to "combat listener fatigue." His Type 2 Mu Stage, published by audioXpress in 2019, introduced a streamlined version with added capabilities. Now, the new Type 3 Mu Stage resulted in what the author believes to be a breakthrough, improving the realistic reproduction of music. This latest iteration of the circuit was prototyped by Kim Bond, an enthusiastic builder of the previous Mu Stages.

This year’s special Glass Audio issue of audioXpress includes interesting explorations such as the Ultra-Linear Power Amplifier by Rudolf Moers, Micro Details in Push-Pull Output Transformers by Hans Polak, Getting Less Gain From Tubes by Merlin Blencowe, and the Type 3 Mu Stage Breakthrough by Alan Kimmel. This issue also includes two speaker designs from Ben (Wolf) Shaffer and Ken Bird, an article about the intriguing return of 78 rpm records, and Paul Marchese’s Part 2 of his insightful Primer on Class-D Amplifiers. Richard Honeycutt shares how he learned to DIY with Tubes.

In this Glass Audio special issue, Menno van der Veen brings us his latest Vanderveen TRANS-PP80 Valve Amplifier, Tom Perazella remakes a famous (Z)OTL amplifier with 300Bs, and Peter Dieleman debunks recurring myths in tube circuit designs. Stuart Yaniger reviews the Hypex NCORE NCx500 amplifier module, while Burkhard Vogel expands his article on Vintage Op-Amp Noise Simulations, and Bruce E. Gillingham concludes its unique MB1 Monoblock Power Amplifier with Precision Bias Control.

This DIY-focused article introduces the Pentriode, a concept to explore the familiar idea of connecting commonly available pentode tubes as triodes, creating a circuit that excels in linearity. The Pentriode is formed by making one simple change to connect the screen grid to the cathode of a cathode follower. The article proposes different possible approaches, including for a mu stage, a design that the author previously wrote about for audioXpress. This article was originally published in audioXpress, May 2022.

More than a decade since the original publication by audioXpress, many readers still actively search for information and share the schematics of this OTL tube project. Tim Mellow's design explores a different output stage using a novel combination of local feedback and current drive in order to achieve good symmetry and cancellation of even harmonics. This article was originally published in audioXpress, February 2010.

Following on the introduction earlier in 2021 of the 6L6GCM-STR, the first model from an all-new high quality premium tube series named REDBASE from Tube Amp Doctor (TAD), the German company now announced the new TAD EL34-STR REDBASE, which can be used for any EL-34 application in guitar amplifiers and also hifi tube designs instead of 6CA7 and KT77 tubes. All tubes in TAD’s REDBASE family are manufactured on a new exclusive production facility.

A few years ago, Jan Didden designed a high-voltage delay unit and shared its details in a 2019 audioXpress article. Many people built it and like it, but others said that it would be totally unnecessary. As so often happens in audio, arguments pro and con raged without a clear resolution. So Didden thought this was something he needed to get his head around. He found several sources, which he thought were credible, and this article is the result of his investigations, fed by those sources. This article was originally published in audioXpress, August 2020.

"There is nothing quite like a quality tube amplifier," states the author in the introduction to this directly heated triode amplifier project. The idea for the amplifier started from the author's discovery of the Loftin-White circuit. The author chose the 2A3 directly heated triode power tube to implement the Loftin-White circuit. The 2A3 vacuum tube is a power triode capable of outputting 3.5 W in a single-ended Class A configuration. This article was originally published in audioXpress, August 2013.