Pro-Ject Optical Box E Phono Stage Black

The Pro-Ject Optical Box E Phono is an MM phono preamplifier with built-in analogue-to-digital conversion, sitting within Pro-Ject’s Box Design E range of compact, affordable audio components. Where a conventional phono stage provides only an analogue output, the Optical Box E Phono adds a 24-bit/96 kHz TOSLINK optical digital output alongside its analogue line output, with both operating simultaneously. This makes it straightforward to connect a turntable to modern audio systems that lack analogue inputs — soundbars, AV receivers with only digital connections, and DAC-based setups all become accessible without an additional converter in the chain.

Connectivity & Versatility

The rear panel carries a pair of gold-plated RCA phono inputs with a ground terminal, a 3.5 mm line-level input, a 3.5 mm analogue line output, and a TOSLINK optical digital output. A Line/Phono switch selects between the two input modes. In Phono mode, the unit applies precise RIAA equalisation to an MM cartridge signal; in Line mode, it passes the 3.5 mm input through the A/D converter and outputs it digitally via optical, effectively functioning as a compact analogue-to-digital converter or signal splitter.

Circuit Design

The phono stage section is based on Pro-Ject’s Phono Box E circuit, delivering 43 dB of gain with a noise floor of 74 dB and total harmonic distortion below 0.04%. RIAA equalisation accuracy is specified at ±0.5 dB across the full 20 Hz to 20 kHz range. The internal housing is lined with metal shielding to eliminate RF interference and mechanical vibrations, and the unit runs from an external 18V DC power supply to keep mains noise out of the signal path.

Practical Applications

The simultaneous analogue and digital outputs enable flexible routing. A turntable can feed a traditional stereo amplifier via the analogue output while also supplying a digital signal to a separate room system or recording device. Alternatively, the line input can digitise signals from tape decks, tuners, and other analogue sources for integration into a digital audio chain.