Celestion Introduces Truvox 1225 Midbass Loudspeaker

Celestion continues to expand its revived Truvox catalog, revitalizing a legendary brand that is part of the company’s centennial history. The most recent product is the Truvox 1225, a new 12” midbass driver offering exceptional performance at a highly competitive price point. As is the case with previous Truvox drivers the 1225 is a drop-in ready solution for sound reinforcement applications, delivering superior power handling, durability, and sound quality.

Brian Lowe (Belleson) developed a unique custom-designed transconductance amplifier (Bel Amp) with fully differential (balanced) low-noise JFET inputs and current output. it offers 50dB of current gain prior to any voltage excursion, virtually eliminating distortion caused by voltage-dependent node capacitance exhibited by more conventional approaches. This is the second article detailing the op-amp design, containing simulations and measurements.

This project describes a dynamic compressor circuit working in reverse. Instead of limiting the maximum volume level of an audio signal, it leaves loud parts alone and instead raises the volume when it’s too soft. The project uses a famous VCA circuit designed by David Blackmer of dbx fame, developed in the 1960s, whose patent expired long ago. The resulting original design is useful for transcribing conference meetings, court reporting, or any other situation where the volume level of recorded speech can vary by a large amount.

The continuation of this 60-Watt Class A amplifier project, named the ax-Amplifier, this design uses Augmented Feedback Error Correction (AFEC) to achieve ultra-low distortion and improve key audio performance parameters without adding too much complexity and cost. The first part of this article described the amplifier design in detail. This second part details the power supply system and conclusion with measurements. This article was originally published in audioXpress, May 2024.

From the experienced hands of Andrew C. Russell, of Hifisonix fame, comes the ax-Amplifier, a Class A design that uses Augmented Feedback Error Correction (AFEC) to achieve ultra-low distortion and improve key audio performance parameters without adding too much complexity and cost. Published in two parts, the first article addresses the amplifier design in detail, with Part 2 detailing the power supply system and conclusion with measurements. This article was originally published in audioXpress, April 2024.

This article details a lifetime project from audioXpress' technical editor Jan Didden. After a successful restoration project of a pair of precious ESL-63 Quad electrostatic speakers, he opted to design and build the eDD, a well-performing high voltage amplifier to directly drive electrostatic speakers. This challenging but successful DIY project with a design goal of 1500V RMS at 20mA RMS over the full audio band, took a while to complete but was a success. This article shares every step of the construction.

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

The first article from audio expert Ethan Winer about Modern PCB Design Practices, gave a general overview of board design using surface-mounted devices (SMDs). The article examines current practices and methods for designing four-layer printed circuit boards using surface mounted components (SMDs), and this second part explains specific strategies and related issues to deal with the design and production of great quality PCBs. This article was originally published in audioXpress, March 2023.