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.

The two authors investigate leakage loss as identified with an advanced transducer model and verified with measurements. This is compared to classical Thiele-Small modeling with the intention to motivate the reader to further explore advanced parameter estimation and box simulation with the Speakerbench Speaker Design Calculations online tool. This two-part article concludes with an overview of how Speakerbench offers an accurate and practical approach to this problem. This article was originally published in audioXpress, August 2021.

In this article for Voice Coil, the two co-founders of Purifi Audio share some details about the company's unique research with loudspeakers, and reveal their findings in looking for the roots of speaker nonlinearities and distortion mechanisms. A research effort that the authors believe deserves consideration from the industry, as a new set of standard parameters that should be included in datasheets. This article was originally published in Voice Coil, August 2021.

Primarily targeted at production test applications, the APx517B debuted at the end of 2020 and supplements AP's powerful product line of analyzers, which are considered the gold standard in audio measurement. In his review, David Logvin explores audio measurements with this fully integrated hardware, that combines multiple digital interface options all with accredited calibration. This article was originally published in audioXpress, August 2021.

"Before you start measuring and playing around with your new speakers, maybe you should know your room." The statement, inspired Ethan Winer to write this article from a very practical perspective, helping us to understand the acoustics of our own listening rooms, and how measurements will help us. The examples contained in the article use the popular Room EQ Wizard (REW) software. This article was originally published in audioXpress, August 2021.

It's time for Loudspeaker News and Developments, unique technology Spotlights, valuable industry Directories, great speaker patent reviews, and Vance Dickason's speaker driver characterizations in Test Bench. This month, Bruno Putzeys and Lars Risbo write about their speaker research for Purifi Audio, James Croft reviews an acoustic low-pass filter patent awarded to Bujeon, and Vance Dickason tests the 5CXN44 coaxial driver from B&C Speakers. This edition features updated directories of Voice Coil and Magnet Vendors and Distributors.

The August 2021 edition of audioXpress is now available in print and online. Read our Acoustical Solutions Round-Up 2021 and enjoy the DIY perspectives from Ethan Winer and Thomas Perazella on dealing with room measurements and treatments. David Logvin reviews Audio Precision's APx517B Acoustic Audio Analyzer, while Richard Honeycutt reflects on acoustic challenges for online and in-person meetings. And we conclude the DH-220C MOSFET Power Amplifier article by Bob Cordell and Rick Savas, and the VSCS Amplifier project in this edition.