You Can DIY! Building a Guitar-Controlled Synthesizer: LFO and ADSR

This third article continues to follow Ethan Winer's fascinating journey of building modules for a Guitar-Controlled Synthesizer. The two previous articles described the core circuits he developed for this project that uses an electric guitar instead of a keyboard to control an analog synthesizer. This article continues with two components that are essential for all analog synthesizers: The Low Frequency Oscillator (LFO) and the Attack Decay Sustain Release (ADSR) envelope generator. Both of these circuits generate voltages that control other modules in the synthesizer. This article was originally published in audioXpress, June 2022

There's a lot of everything in audioXpress October 2022. Starting with a market update on audio for Residential Integration. Next, Jonny McClintock shares The Story of aptX, Gary Galo reviews Sumiko phono cartridges and new 78 rpm stylus, Richard Honeycutt explains RT Measurement, Frans de Wit tackles the design of a DC Power Supply, Ken Bird builds a pair of tower speakers with Oaktron drivers manufactured in the US, and Christopher Paul writes about Triode Common Cathode Stages and its controversies.

This DIY-focused article introduces the Pentriode, a concept to explore the familiar idea of connecting commonly available pentode tubes as triodes, creating a circuit that excels in linearity. The Pentriode is formed by making one simple change to connect the screen grid to the cathode of a cathode follower. The article proposes different possible approaches, including for a mu stage, a design that the author previously wrote about for audioXpress. This article was originally published in audioXpress, May 2022.

This is the second article in a fascinating DIY journey of a guitar-controlled, all-analog synthesizer project that will include multiple stages and modules. Following a Sample & Hold circuit designed to retrieve previous voltages that no longer exist, this article details voltage control and how the playing is converted to voltages and back to frequency.

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.