Many hi-fi enthusiasts in Elektor’s community agree that vinyl offers a unique sound that stands apart from digital audio sources. In a 2016 article, we presented a high-end phono preamplifier that utilized four specialized op-amps in parallel for each channel to deliver exceptionally low noise. This phono preamplifier design approach revisited a concept that Elektor first explored in 1982, when the designers used discrete transistors to achieve similar results.

Phono Preamplifier Background

Audio circuits have long been a favorite topic for Elektor community members. Over the years, Elektor has developed and published countless designs, many of which were both innovative and unique. One standout was the “super low noise phono preamplifier,” featured in the 1982 Summer Circuits issue, Thomas Scherer explained. The name "supra" is derived from the Dutch term “super ruisarm,” meaning "super low-noise." The design featured eight affordable low-noise BC550/BC560 transistors in parallel at the input stage of each channel, which effectively reduced noise by a factor of √8, or 2.82. This was a notable improvement, especially for moving-coil (MC) pickups, known for their very low output signal. However, the design required a large circuit board, with each channel using a total of 20 transistors.
 
The PCB layout for the phono preamplifier. All components are leaded (through-hole) types.

Construction and Packaging

"Before you start building the preamp, you have to decide which configuration you want to make," Scherer explained. "In our prototype we opted for the combination of the preamp board and the modular power supply board. They both fit nicely in the Hammond enclosure specified in the components list. Board assembly should not present any problems even if you don’t have advanced soldering skills."

The preamp board fits precisely in the bottom slots of the Hammond enclosure. Mount the Cinch sockets and the ground terminal on one of the end panels
 
The phono preamplifier board and power supply board mounted one above

Phono Preamplifier Circuit

Despite the paralleled op-amps, the schematic diagram is fairly compact, Scherer noted. Each channel requires four input op-amps and an additional dual op-amp, which in this case is an LM833. The component values on the schematic are intended for MM/MD pickups with a rated output signal level of approximately 2 mV. The circuit can also be adapted for MC pickups with low output signal levels by adjusting a number of resistor values.
 
Click the image to access the entire schematic.

The Original Project

The phono preamplifier article, “Supra 2.0: A super low-noise MM/MD phono preamp," appeared in Elektor July/August 2016. It will be free to download for the two weeks following the publication of this news item. Enjoy!
Editor's Note: This article (150616) was first published in a 2016 edition of ElektorMag. Some of the components, products (e.g., PCBs), and links may no longer be available. Still, the educational content remains valuable, and we trust that it will inspire you to start a new project.
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