Phono Equalizer Amplifier Dedicated to the DS-E3 Optical Cartridge Pt.1

Challenging the Latest Devices with a Vacuum-Tube Circuit by Hiroshi Ueno

This equalizer amplifier was designed for DS Audio’s DS-E3 optical cartridge. The signal path is a pure vacuum-tube configuration using 6922/E88CC tubes. Particular attention was paid to high quality in the LED power supply and the PD (photodetector) bias power supply, both of which have a major influence on sound quality. This article explains in detail the concept and design method for the equalization circuit used in an equalizer for optical cartridges. The amplifier is also equipped with a function that changes the sound quality by varying the load on the secondary side of the input transformer.

A Breakthrough in Analog Disc Playback

Among audio enthusiasts, the eternal question—“Which is better, analog or digital?”—continues to provoke lively debate. Today, digital audio technology has made remarkable progress. However, in the process of “quantization,” in which a music signal is converted into digital data, specifications such as bit depth and sampling frequency set the upper limit of playback quality. Even the highest-grade format, DSD (Direct Stream Digital), is not free from these limitations.

Analog discs, referred to hereafter simply as “analog,” have fewer specification-based restrictions. On the other hand, their biggest problems are time-axis fluctuation and a relatively high noise level. For this reason, the equipment required for playback must have higher rotational accuracy and lower noise. Put another way, this means that “the more money and effort you invest, the better analog can sound.”

In 2025, I had the opportunity to speak with representatives from several specialist audio manufacturers that continue to focus their development efforts on analog. Several of them pointed out that “digital loses spatial information and has an upper limit in quality,” whereas “analog still has room for improvement if cost is invested.” With this in mind, I designed and built an equalizer dedicated to DS Audio’s DS-E3 optical cartridge, which has become a topic of interest in the audio industry.

Whether the optical cartridge will truly become a breakthrough in analog disc playback remains to be seen. I hope to play it on various occasions, have many people listen to it, and receive their evaluations.