Joachim Gerhard on Low Noise Phono Stages: The Discrete INA Design

Ask audio industry insiders and audiophiles alike about Joachim Gerhard, and chances are that they mention the many high performance speakers he designed over the years. But he also has a great track record designing phono preamps and this interview explores that aspect of Joachim’s career. In this second part of the interview, Jan Didden explores Gerhard's design ideas and goes into details on his Discrete INA design, a discrete input stage instrumentation amplifier topology.

Ask audio industry insiders and audiophiles alike about Joachim Gerhard, and chances are that they mention the many high performance speakers he designed over the years, initially for Audio Physic, currently for Suesskind Audio. But Gerhard also has a great track record designing phono preamps. This interview explores that aspect of Joachim’s career. In the first part of this interview Joachim discusses the design considerations and circuit topologies for low noise phono stages, culminating in his very low noise and Flexible Phono Stage (FPS) design. This article was originally published in audioXpress, September 2024.

Europe’s Nordic countries have long been the birthplace for high-quality and innovative audio products, particularly excelling at speakers and amplifiers. Located near Copenhagen, ICEpower has traditionally been known as a purveyor of high-performance Class-D amplifiers and associated switch-mode power supplies. The company continues to provide innovative Class-D solutions today, but its scope is now much broader than that, as this report discloses.

Series voltage regulators are a great way to provide almost-noise free and rock-stable DC to your audio circuits. But the load current often has distorted signal components that can generate a ‘dirty ground’ across the supply ground wires and tracks. This can introduce distortion components in other circuit sections using this ground. With shunt regulators we can keep the dirty ground localized and largely avoid the problem. Technical Editor Jan Didden explains.

Robert Munnig Schmidt is intrinsically connected with advanced motion systems and motional feedback applications. He is now retired from his own consultancy business, following an outstanding career that includes key R&D positions at Philips, being part of the ASML founding team, and teaching Mechatronic System Design at the Delft University of Technology. In this interview, Schmidt revisits the theory and practice of motional feedback, silicon wafer steppers, voice coils, Class-D amplifiers, and much more.

audioXpress traveled to Germany to learn about the Pure Acourate Sound Project, which aims to create the lowest distortion sound in a listening room. The initiators of the Pure Acourate Sound project are Ulrich Brüggemann, Markus Grelka, and Ralf Höllmann. The partners involved in this unique system are Purifi Audio, Okto Research, GIK Acoustics, Klippel, Roon, AudioVero, Rose Handwerk, and Joachim Gerhard. Ahead of the presentation at the May 2024 Munich High-End show, audioXpress offers a preview of the project.

In analog audio, you often must connect a source to a “receiver” unit. Pre-amp to power amp, phono preamp to an active crossover, the crossover to the power amp, that sort of stuff. Each of these units has an input impedance and an output impedance spec. I often get questions like: “My power amp has 20kΩ input impedance, my preamp has 100Ω output impedance, and maximum load is specified as 10kΩ. Will that work together or will I break something?”. Jan Didden explains all about Input-Output Impedance Matching.

Regulator Needed for Stable, Noise- and Ripple-Free DC Relationship. Does your nice circuit get what he needs from the power supply? Jan Didden explores when a regulator is a regulator. ...when it regulates, you’d think. Yet, in many online fora and discussions you see circuits that ‘do something’ but there’s absolutely no regulation taking place.

Whether it is power amplifiers, vinyl reproduction preamplifiers, active crossover filters or, as in this case, small-signal circuits for a very wide range of applications, Douglas Self is one of those authors who consistently has produced reference works about technical audio. You may think that as a fourth edition, it would just be a refinement on the three editions that went before it but Self always adds new material and new insights to make it worthwhile to get this new book.

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.