You Can DIY! Passive Preamp: Transformer Implemented

In this article, Jack Elliano the founder and principal designer behind Electra-Print Audio, details a simple but very interesting concept of a line amplifier using step-up transformers plus a variable gain control, offering usable results from low impedance sources. The preamplifier project uses Electra-Print handcrafted transformers, which the company manufactures for its own high-fidelity tube audio components, directly from its home base in Las Vegas, NV. This article was originally published in audioXpress, January 2005.

One of the problems when designing large audio devices, (e.g., mixing consoles) is the enormous amount of wiring that’s needed. In this article for audioXpress, Ethan Winer writes about the practical ways on how to deal with wiring techniques in order to reduce the amount needed for any given project by using rotary encoders, serial communications, and other clever solutions. This article was originally published in audioXpress, March 2021

In this article, Mark Driedger revisits “The Remaking of a Champ,” inspired by Kirk Elliott’s original article for Glass Audio (1992). The Fender Champ is considered “the” classic tube practice amplifier and it has been remade a few times over. Driedger created his own version, including a provision to easily try different output tubes. This article was originally published in audioXpress, January 2016.

In this article, Menno van der Veen explains everything about the Vanderveen Trans-SE10 amplifier, which is available as a DIY kit manufactured by Tentlabs. This letter-sized stereo amplifier is a single-ended design with an output power of 10W per channel, but there's a lot "under the hood" (and the glass) to understand. The article explains the “why and how” of the unusual Vanderveen Trans-SE10 design. This article was originally published in audioXpress, January 2021.

In this classic speaker from Speaker Builder, the author proposes a complete project of a speaker design with a pyramid-shaped cabinet. The fact that its nonparallel walls minimize standing-wave effects, and the slanted front improves the time adjustment of the dri­vers, added by the fact that the front is wide enough at the base to accommodate a larger woofer, and narrow at the top, where the tweeter is located, were the fundamental considerations. This article was originally published in Speaker Builder magazine, March 1998.

Arduino boards are extremely popular among DIY enthusiasts and a number of add-ons or “shields” exist, particularly for audio players. Now, the Arduino MKR family has expanded the possibilities even more. This article details an Infineon amplifier board featuring integrated MERUS MA12070P proprietary multi-level Class-D ICs, which create an exciting platform for advanced wireless audio projects — including full-fledged Alexa-powered DIY smart speakers. This article was originally published in audioXpress, October 2020.

Our friend Geoff Hill, the inventor of the original tetrahedral test chamber (TTC), explores how to do loudspeaker measurements at home. For those of us without an anechoic chamber at home, Hill explains how to build our own test chamber. With the build description, he also provides a valuable guide on alternative loudspeaker measurement techniques. This article was originally published in audioXpress, September 2020.

Vented systems are in chronic overload. This article shows how, by applying low-cost digital signal processors (DSPs) to passive radiators, you can extend bass an octave below what is normally considered practical. At the same time you can increase power handling and maximum output, and squeeze high performance from tiny systems. We all know reflex systems are more efficient and offer deeper bass than sealed systems. However, the vast majority still fall short of their potential by 6 to 12 dB or more. Worse yet, often people don’t realize how vulnerable drivers are to damage. Many abuse woofers without knowing it. Few realize how much more sound output is possible from a DSP Assisted Reflex design.

In this article, George Ntanavaras explains how to build a turntable speed measurement device using a microprocessor-controlled device that measures the speed of a turntable's platter. The project uses an Arduino board and the Arduino software IDE, and a micro sensor manufactured by Omron to sense the platter rotation. This article was originally published in audioXpress, June 2018.

Passive crossover filter networks for multi-way loudspeakers generally require a resistive termination for optimum performance. The driver itself generally presents a reactive load. Inductive rise with frequency above resonance of the loudspeaker electrical impedance is semi-inductive due to eddy current losses. The L2/R2 impedance model represents the electrical impedance as seen by the amplifier output. An improved compensation network can be realized by using the analogous circuit “dual” of the L2/R2 model. This represents a dramatic improvement to the basic two-component Zobel network and compensates for the non-ideal semi-inductive behavior of the loudspeaker driver across the entire frequency band.