audioXpress - June 2019

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8 How to Work with an Acoustical Consultant 14 Working with USB-C - What Audio Developers Need to Know 26 Building a Null Tester Device Ethan Winer details the construction and theory behind his Null Tester, which is a device that sends the same audio signal through two paths, then it electronically subtracts one signal from the other to obtain the difference. 30 Restoration and Revival of the McIntosh MC30 (Part 2)- Finishing the Restoration In the second part of this article, Bruce Brown discusses some important information, including the power supply rebuild and some improvements you can make to help your MC30 last another 50 years. 36 Sigma 100 (Part 1)-Designing the Satellite/Subwoofer Loudspeaker System In the first part of this two-part article, George Ntanavaras shares his design for the Sigma 100, a unique loudspeaker system with two satellite speakers and a single subwoofer. 50 Searching for a Unicorn (Part 2)-Generating a Good Signal Source Testing a voltage regulator with exceptionally good performance requires an even more exceptional signal source and measurement setup. In this second of a two-part article, Brian takes us through 10 years of test refinement to measure sub-microVolt ripple across a wide frequency range. 58 Measuring Super Regulators Jan Didden, our technical editor, supplies an informative sidebar about super regulators to enhance the information provided by Brian Lowe in his main feature article. 60 More About Noise in Vacuum Tube Circuits