Optimizing Variable-Frequency Tone Controls

This article describes bass and treble tone control circuits where the frequency at which control begins in each band is variable over a 16 to 1 range, making it much more useful for correcting speaker deficiencies or room anomalies. Something that very few manufacturers have offered. This article was originally published in audioXpress, December 2023.

audioXpress December 2023 includes a market overview of multiroom audio, Brent Butterworth writes about new ways to measure ANC earbuds, and Stuart Yaniger measured the new Axign and GaN Systems Class-D audio amplifier board. Richard Honeycutt writes about tubes, BJTs, JFETs, MOSFETs, and ICs, and Dimitri Danyuk, discusses JFETs in audio circuits. Douglas Self explains how to optimize variable-frequency tone controls, and Jan Didden shares his eDD direct-drive amplifier project.

California-based (and now also Texas-based) Schiit Audio continues to expand it's range of "gotta-have-it" audio solutions, this time focusing on reinventing the equalizer...again. The all-new Lokius 6-band balanced equalizer, builds on the success of the recent Loki Mini+ (highly recommended for Spotify users), taking things to a new level, now with more bands (6 vs 4), as well as balanced and single-ended input and output. Like the Loki Mini+, the new Schiit Audio Lokius is a single-discrete-gain-stage, LC filtered equalizer.

Schiit Audio announced availability of the new Loki Mini+ 4-band equalizer - a simple design for tone control, which the company successfully brought back with the original Loki Mini equalizer, enabling anyone to adjust their speakers or headphones' response without degrading the audio. The new Loki Mini+ builds on the performance of Schiit’s original Loki Mini, with significantly lower noise, lower distortion, optimized frequency bands, and cosmetic refinements. Still, the new Loki Mini+ remains the same price as the outgoing Loki Mini, at $149.

Peter Delos details how to add tone controls to a three-channel tube-based guitar preamplifier. The circuit is a versatile building block anyone can use for his or her own preamplifier applications. The project is implemented with three 12AX7 gain stages. The tone control at the final output is a standard bass, mid, treble control circuit found in many guitar amplifiers. This article was originally published in audioxpress, October 2014