Pro-Ject - Phono Box RS

Pro-Ject’s reference-line phono stage: true dual-mono, balanced XLR on both input and output, a stepless 10–1200Ω loading control on the front panel, and a Decca curve as well as RIAA. Discontinued and superseded by the RS2.

The Phono Box RS is the box where Pro-Ject stopped making a small black accessory and started making a component. It is 2kg, 206mm wide, built as a true dual-mono design with completely separate left and right signal paths, and it has balanced XLR sockets on both the input and the output — so a balanced-output turntable like the X1 B can stay differential from cartridge clips to preamp.

The loading arrangement is the part that matters most in use. Rather than a fixed set of impedance steps, the RS gives you a stepless rotary control on the front panel covering 10Ω to 1,200Ω, working together with DIP switches on the rear. That means you can sit with a record playing and dial in a moving-coil’s loading by ear rather than by guesswork, which is a genuinely different experience from flipping a DIP switch, unplugging, replugging and listening again. Capacitance is switchable across 100, 200, 300, 420 and 520pF for moving-magnet use.

There is a Decca equalisation curve alongside RIAA on the front panel. Decca’s ffrr curve differs from RIAA and a substantial body of British pressings from the 1950s were cut to it. If you own that material, this is a switch you will actually use. Pro-Ject does not offer Columbia or Teldec curves on this unit and we will not claim otherwise.

Pro-Ject is candid in the RS datasheet about what is inside: Analog Devices SSM2019 instrumentation amplifiers at the input and Linear Technology LT1010 high-current buffers at the output. This is an integrated-circuit design rather than a discrete-transistor one, executed with named, well-chosen parts. Distortion is a published 0.019% and the noise floor is 91dB A-weighted.

This model has been discontinued and replaced in Pro-Ject’s range by the Phono Box RS2, which is a different unit with a different gain ladder and a much larger 20V/3A power supply. The specifications below are the original RS’s, taken from Pro-Ject’s own datasheets and manual.

Features

• True dual-mono design, completely separate left and right channels
• Balanced XLR and unbalanced RCA on both input and output
• Stepless 10–1,200Ω loading, set by a front-panel rotary control
• Five switchable capacitance values from 100 to 520pF
• RIAA and Decca equalisation curves, selected from the front panel
• Subsonic filter at 20Hz, 12dB per octave
• Analog Devices SSM2019 input stages and Linear Technology LT1010 output buffers
• Front-panel mute as well as power

Specifications

• Status: Discontinued. Superseded in Pro-Ject’s range by the Phono Box RS2, which is a different unit — the figures below are the original RS’s
• Type: Moving-magnet and moving-coil phono preamplifier, true dual-mono
• Cartridge support: MM, high-output MC and low-output MC. Selected by a rear-panel F/V rocker switch
• Gain: 40dB and 50dB (B) / 60dB (A) from the RCA outputs, where B is MM and high-output MC and A is low-output MC. Add 6dB when using the XLR outputs, giving 46, 56 and 66dB
• Input impedance: Stepless variable, 10Ω to 1,200Ω, by front-panel rotary control; plus a fixed position (given as 10Ω in the datasheet spec table and as 10Ω or 47kΩ in the English datasheet body text)
• Input capacitance: 100 / 200 / 300 / 420 / 520pF, by DIP switch on the rear panel
• Where the controls are: Front panel: input gain rocker, RIAA/Decca selector, variable impedance rotary, on/mute, power. Rear panel: capacitance and impedance DIP switches, and the F/V cartridge-type rocker. There are no underside switches
• Output level: Not published by Pro-Ject
• Output impedance: 50Ω
• Noise floor: 91dB A-weighted; 80dB unweighted. Pro-Ject publishes one combined figure and does not split it by MM and MC
• THD: 0.019%
• RIAA accuracy: Within 0.3dB, 20Hz–20kHz
• Alternate EQ curves: RIAA and Decca, front-panel selectable. Columbia and Teldec are not offered
• Subsonic filter: 20Hz, 12dB per octave
• Inputs: 1 pair RCA and 1 pair balanced XLR
• Outputs: 1 pair RCA and 1 pair balanced XLR
• Circuit: True dual-mono. Analog Devices SSM2019 input stages, Linear Technology LT1010 high-current output buffers — an integrated-circuit design, not discrete
• Channel separation: Not published. Pro-Ject publishes no channel separation or crosstalk figure for any product in the Phono Box or Tube Box range.
• Power supply: External. Pro-Ject’s manual and German datasheet give 2 x 18V / 250mA DC; their English datasheet gives 2 x 18V / 300mA DC. Consumption 150mA DC, under 1W in standby
• Dimensions: 206 x 72 x 200 mm (W x H x D); 210mm deep including sockets
• Weight: 2,000g without the power supply
• Country of manufacture: Not published. Pro-Ject’s documents give Vienna, Austria only as the company address, which is not a manufacturing location
• Warranty: Two years from date of purchase, extendable to three years by registering the product with Pro-Ject and subscribing to their newsletter. Pro-Ject states that warranty is administered by the local distributor and that terms can vary by region; no separate United States term is published. Coverage requires purchase from an authorised dealer — The ’In Groove is one.