Development and Design: Sound Level Evaluation for Raspberry Pi 4

This article proposes a Sound Level Evaluation solution based on the popular Raspberry Pi 4 and the possibilities of using the Sfera Labs' Exo Sense Pi - a compact multi-sensor module - as a sound meter. The Exo Sense Pi combines several environmental sensors and connectivity options, and integrates a digital microphone which can be used to evaluate ambient noise levels or measuring noise sources. This article was originally published in audioXpress, March 2022.

A serious electronics enthusiast with an engineering background, when Reinhard Metz set out on this design the main goal was to create a straightforward stereo source selector, monitor selector, volume control, and line amp, and not much more. The resulting preamplifier, with 8 inputs, including MM phono, plus 4 recording outputs and a front panel headphone output, is a popular project. This article was originally published in audioXpress, August 2010.

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.

For those readers following the fascinating article series by Morty Tarr on "Cascodes, Folded Cascodes, and Current Mirrors," this final article in the series contains an additional section with important aspects of amplifier design. In the first two parts of this article series, Tarr discussed the technical merits of cascodes and related circuits. This useful addendum covers a simple test circuit for matching FET devices, the fascinating story of the Blowtorch Line Stage design, and additional notes on inverting and non-inverting amplifier stages and integrators. This article was originally published in audioXpress, December 2021.

In Part 1 of this three-part article about circuit topologies that are used to provide specific functions for an amplifier design, the author discussed cascodes and folded cascodes. In this Part 2, he focuses on current mirrors and line stages. As the author writes, “As designers, we have many devices to choose from. Some devices are ideally suited to certain tasks. Other tasks require performance that is difficult to achieve. While many excellent devices exist today, ideal devices do not exist, except maybe in Spice simulations.” This article was originally published in audioXpress, October 2021.

For this audio electronics article, Morty Tarr wrote a fascinating exploration of circuit topologies that are used to provide specific functions for an amplifier design. Cascodes, folded cascodes, and current mirrors are some of these topologies, intended to improve the performance of the devices, but which also add complications. In the first of a three-part series, the author discusses cascodes and folded cascodes, useful to improve high-frequency response and device linearity.

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.

This article offers the first serving of an amazing DIY project from amplifier experts Bob Cordell and Rick Savas with an upgrade for the legendary Hafler DH-220 lateral MOSFET power amplifier. The design is implemented on two PCBs, one as a drop-in replacement for the original Hafler circuit board and the other as a new board that consolidates all of the output stage wiring and components within the heatsink and under the main PCB. This article was originally published in audioXpress, July 2021

In the first part of this work, the authors discussed the difficulties in estimating cabinet losses using the classical Thiele-Small framework, and proposed a solution using an advanced transducer model. In this second article, the authors detail how their Speakerbench web-app offers an accurate and practical approach to this problem, and demonstrate how users will be able to easily and accurately determine the best suitable box volume for a loudspeaker system. This article was originally published in audioXpress, September 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.