You Can DIY! The DH-220C MOSFET Power Amplifier - Part 2 Construction and Testing Instructions

This reference DIY project details of an upgrade construction for the legendary Hafler DH-220 lateral MOSFET power amplifier, which can also be used to upgrade other Hafler models or even inspire new designs. The design is implemented on two PCBs, one as a drop-in replacement for the original Hafler circuit board and another board that consolidates all of the output stage wiring and components within the heatsink and under the main PCB. After the authors detailed the design and performance of the DH-220C upgrade amplifier, in this second part of the article, Bob Cordell and Rick Savas discuss the construction and testing. This article was originally published in audioXpress, August 2021.

In this article, Scott Dorsey shares his unique experience-based tips for converting a classic Brüel & Kjær measurement microphone system into a valuable recording microphone. Vintage instrumentation Bruel's (the ancestors of the DPA's) are great microphones that can be found on the surplus market and are appropriate to use for recording applications, if you know which ones and how to convert them. This article was originally published in audioXpress, July 2016.

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 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.

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.

Infineon Technologies developed the world’s first fully self-contained Raspberry Pi audio amplifier HAT (Hardware Attached on Top) board. It offers high definition audio at boombox power levels in a small form factor. The Infineon proprietary multilevel technology ensures minimum size and consumption, state of the art power efficiency, and high resolution audio quality for Raspberry Pi users and makers. Target applications include active speakers with wireless music streaming.

This project is a great suggestion for a new affordable high-end 2 x 40 W Class D audio amplifier implemented with a Hardware Attached on Top (HAT) board to connect onto a Raspberry Pi Zero platform, creating a solution ideally suited for DIY audio projects. On the other hand, this is a very clever way to promote the Merus amplifiers from Infineon and get a great number of developers and enthusiasts to actual use it, get to know it, and understand its advantages in a real audio project. This article was originally published in audioXpress, January 2020.

The November 2019 edition of audioXpress is now available with a wide range of technical topics in audio electronics and design. We review the Benchmark LA4 Line Amplifier and the new Hooke Verse Bluetooth Binaural Recording Headphones. Jan Didden proposes an updated version of his High-Voltage Delay for Tube Amplifiers, and Thomas Zarbo, Jr. explains how to build his Tenacious Bass-8 Powered Subwoofer. And, learn more about Data-Over-Sound, MU amplification topologies, and Auverdion’s Aurora open-source DSP platform. Now available!

In this project for audioXpress magazine, Jan Didden offers a modern update on his original 2014 high-voltage delay design, which he built to complement tube amplifiers. The new unit needs no additional outside power, and allows setting the delay between 20 seconds and 254 seconds, which should cover all requirements. The article describes the complete project, and there's a DIY kit available at diyaudio.com. This article was originally published in audioXpress, November 2019.