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.

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.

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.

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.

This article is the final part of Peter Larsen's tutorial for the design of a complete loudspeaker from transducer to final product. The first two parts of this Loudsoft simulation software system design tutorial series demonstrated the development of a 6.5" woofer and vented enclosure along with a 1" silk dome tweeter. The final step is an appropriate passive network design, which is where FINE X-over software comes to the rescue.

This is the second part of Peter Larsen's tutorial for the design of a complete loudspeaker from transducer to final product. The target design is a two-way speaker with a 6.5" woofer and a 1" dome tweeter. Having previously explained the woofer design, in this second article, Peter Larsen explains the process for a 1" silk dome tweeter.

For Voice Coil, Peter Larsen developed a tutorial for the design of a complete loudspeaker from transducer to final product. A great way to gain a practical perspective of the whole family of Loudsoft software tools. The target design will be a two-way speaker with a 6.5" woofer and a 1" dome tweeter, and this issue contains part one of this valuable exercise.

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.