From the Vault: The Borbely Preamp

"Designing a preamp is probably the most challenging engineering task in the audio chain, and many designers have invested a lot of time and effort in it," wrote Erno Borbely in this original 1985 article for the Audio Amateur. "My reason for designing this preamp is quite simple: I wanted to have a top-quality preamp without paying megabucks for a Levinson or Accuphase unit. It is up to you to decide whether or not I have succeeded in achieving the same quality." This article was originally published in The Audio Amateur Issue 4, 1985, and is still frequently referenced.

To reproduce an audio signal faithfully over the whole audio band, your circuit needs to have a bandwidth at least as large as the audio band. But that’s not the only requirement: your circuit needs to maintain that bandwidth from the lowest to the highest signal level. That’s where the crux lies: it is relatively easy to get a nice wide bandwidth for small signals, only to have it breakdown with high signal levels due to the dreaded slew rate limiting.

In this second article, Brian Lowe (Belleson LLC) continues his search for the Unicorn of "Measuring Voltage Regulator Ripple Rejection," this time focusing on the test fixtures. Testing a voltage regulator with exceptionally good performance requires an even more exceptional signal source and measurement setup to measure sub-microVolt ripple across a wide frequency range. Complementing the final article, Jan Didden, offers an informative sidebar about super regulators. This article was originally published in audioXpress, June 2019.

In this article Brian Lowe shares a fascinating journey in his search for a "Unicorn" that is measuring voltage regulator ripple rejection - or power supply rejection ratio (PSRR). Lowe is the founder and principle engineer at Belleson, LLC, and he has devoted a lot of time to this fascinating "quest." This article was originally published in audioXpress, May 2019.

I completed the design and construction of an archival phono preamplifier, which provides variable equalization along with several other operational necessities for playing vintage records (78-rpm discs, pre-RIAA LPs, lacquer transcription discs, and so on). When it came to selecting topologies for the balanced inputs and outputs, I ruled out transformers due to high cost, physical bulk, and weight. The most practical choice, in terms of size and cost, are the balanced line driver and receiver ICs made by THAT Corporation. This article was originally published in audioXpress, June 2010

In this project article for audioXpress, George Ntanavaras describes the design and construction of a high-quality RIAA preamplifier for moving coil cartridges based on high-quality Analog Device AD797 op-amps designed for low-noise audio applications and driven from very low source impedance. This article was originally published in audioxpress, March 2014.

This article describes a spreadsheet program for designing low-voltage power supplies using common IC three-terminal regulators. The spreadsheets are in standard Excel format, and should work in just about any spreadsheet program. Each file has two main pages: one for use with common variable-output regulator chips, the other for fixed-output devices. This article was published in audioXpress, March 2010.

Michael Kiwanuka’s article “Current Feedback and Voltage Feedback Fallacies” (audioXpress June 2017) elicited comments from Walt Jung, with supporting signatures from a number of well-known designers, to which Kiwanuka responded. Since some editing errors have crept into the article, we decided to make available a complete correct version of the article, together with the mentioned comments and exchange.

If you have a passion for high-quality audio experiences you know this is a continuous learning process. In audioXpress June 2017, you will learn more about binaural recording, how you can tune your listening to your own hearing when using earphones and headphones, and we explain how to assess audio quality in any acoustical environment with the MATT Test. That and much more is now available in audioXpress June 2017.

In April and May 2007, audioXpress published a two-part article by Walter G. (Walt) Jung, noted designer and author of the IC Op Amp Cookbook and IC Op Amp Applications book series. In this article - still being referenced to date - the author discusses audio current regulator circuits and their performance with regard to power-supply-related noise. Read the two-parts plus addendum letters.