You Can DIY!: High-End Class-D Audio Board for the Arduino MKR Family

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.

Another great research article from Ethan Winer, where he designed a simple device that measures capacitor distortion using a USB sound card and free software to try and determine the importance of high-quality capacitors in the signal path. This article details the results of his tests with different capacitor types. This article was originally published in audioXpress, May 2020.

In this article for audioxpress, Ed Simon writes: "There seems to be controversy over what testing means in audio. Measuring a difference does not mean you can hear it. On the other hand, if my ears tell me there is a difference between two audio chains and I cannot measure it, that does not mean it is not there. Probably, I'm just using the wrong method to determine audio differences." And after trying to measure all sorts of things to compare which ones sounded fine - or not - he decided the next step would be to build a dedicated more sensitive measurement. This article was originally published in audioXpress, November 2009.

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.

This approach to RIAA equalization results in a high-quality phono preamp featuring the high-transconductance 5842 tubes. The author adapts Erno Borbely's project of a transistorized phono preamp with a vacuum tube implementation. These articles were originally published in audioXpress, October 2003 and January 2010. For this repost, we decided to merge the two articles in one single page.

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.