You Can DIY! Build the Popping P Filter

This original circuit effectively removes the low-frequency impulses caused by air blasts from a person speaking or singing into a microphone, as well as "plosives." This analog circuit removes these irritating sounds in real time, directly at the source by applying a 24-stage all-pass filter to delay only the lower frequencies of the main audio stream. This original circuit for non-commercial use is available for licensing for commercial manufacture. This article was originally published in audioXpress, October 2023.

For the speaker builders, Perry Marshall details everything there is to know about his beautiful Live-Edge Dipoles project. A design that was inspired by two slabs of birch the author brought home, allowing to finally bring to fruition his idea to build these dipoles. Marshall reveals all the specifics of the driver choices, radiation pattern, and crossovers, while explaining the effects of the obtained radiation pattern and how the speakers behave in practice. This article was originally published in audioXpress, January 2021.

An audio load is an essential piece of test equipment for any audio electronics workshop. Having created the very popular Heathkit ID-5252, more than 35 years ago, Gary Galo decided to design a new option for everyone to build now. The ID-5252 contains four 8Ω, 60W power resistors. The biggest limitation of the Heathkit load is power handling. Series and parallel combinations can be used to produce various resistances and power levels — up to 240W at 8Ω, using all four resistors. But, simultaneously testing both channels of a high-powered amplifier requires two ID-5252 units. Fortunately, the raw parts for building an audio load are easy to find.

Focusing on a practical, hands-on perspective, George Ntanavaras, details the design and construction of a phono preamplifier for Moving Magnet (MM) cartridges and a Line/Headphone amplifier with two additional inputs and volume control. All the amplification stages are based on top-quality audio op-amps such as Texas Instruments' OPA1642 for the phono stage and OPA1612 for the Line/Headphone stage. Almost all the components of the device are contained on a single PCB for easy construction. This article was originally published in audioXpress, February 2022

Most of our readers still remember Tom Perazella’s extraordinary egg speaker project with SB Acoustics Satori drivers, featured in the September, October, and November 2018 issues of audioXpress. Inspired by that design, Metz decided to build his own version, and also explore his own take with an active crossover tri-amp approach using a miniDSP 4x10HD system feeding a dedicated six-channel amplifier using Purifi 425W Class-D units. The new Egg Speaker Amp and System is an inspired take on the original. This article was originally published in audioXpress, July 2022.

Ethan Winer offers his fifth Guitar-Controlled Synthesizer article where he describes how to make two key modules needed by every analog synthesizer: the Voltage Controlled Amplifier (VCA) and Voltage Controlled Filter (VFC). This article explains two different VCA circuits, with a simpler one that works fine for one-off projects where precise unit-to-unit repeatability isn’t needed, and a second circuit similar to the VCA in the original Moog synthesizers. This article was originally published in audioXpress, August 2022.

The three previous articles described circuits that Ethan Winer developed for his current project that uses an electric guitar instead of a keyboard to control an analog synthesizer. This article continues with two pieces needed to process input from an electric guitar: the input section’s preamplifier and noise gate, and the pick detector. The preamp amplifies the weak signal from an electric guitar’s pickup and brings it up to line level for further processing. The noise gate detects when a note is currently playing and when it stops. Of course, the pick detector signals each time a new note is picked.

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

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.