Pro-Ject Phono Box DS3 B silver

Pro-Ject Phono Box DS3 B: balanced and discrete phono preamp

At Pro-Ject Audio Systems, balanced connections had until now been reserved for the RS range, the top of the catalog. The Phono Box DS3 B adopts several technologies from the Phono Box RS2 (balanced gain stage, passive RIAA equalization, continuous impedance adjustment via potentiometer) and makes them available in a compact format made in Europe. Successor to the Phono Box DS2, it adds XLR connectivity, a fully discrete circuit without operational amplifiers, and a dual-mono design.

A balanced gain stage with no operational amplifiers

The “B” in the name stands for “Balanced.” The gain stage of the Phono Box DS3 B operates in fully balanced mode: the signal is processed in two separate chains (hot and cold), each with its own amplification section. This differential processing rejects interference picked up during transmission, since any noise common to both conductors is subtracted when the signal is recombined.

The entire audio circuitry relies on discrete components (transistors, resistors, individual capacitors) with no operational amplifiers anywhere in the signal path. After years of comparative listening tests, Pro-Ject considers that discrete circuits deliver a more neutral and more dynamic sound than integrated circuits. The number of components used is far greater than in an op-amp phono preamp, which makes manufacturing more complex but aims for a measurable qualitative gain.

Passive and separate RIAA equalization

The RIAA equalization stage is also fully passive and discrete. The correction is split into independent sections, an approach that promotes better impedance matching and reduces deviation from the theoretical RIAA curve. Pro-Ject states an accuracy of less than 0.25 dB over the 20 Hz – 20 kHz range, a figure that puts the DS3 B at a level of rigor usually associated with more expensive devices. The Phono Box RS2, with its ±0.4 dB accuracy, actually shows a wider tolerance on this parameter.

The XLR outputs benefit from a dedicated discrete balancing stage, while the RCA outputs have their own discrete output stage fed directly by the RIAA equalizer. The two output paths are independent.

Continuous impedance adjustment while listening

The large front-panel potentiometer, inherited from the Phono Box RS2, allows the load impedance to be varied continuously from 10 to 1,000 ohms, with no clicks or steps. This system, patented by Pro-Ject Audio Systems, allows transparent adjustment during playback: it is possible to turn the potentiometer while listening to a record and immediately hear the effect of the impedance change on the sound. Finding the right load value for an MC cartridge becomes an empirical, fast, and intuitive process.

For MM cartridges, the impedance is fixed at 47 kΩ. The load capacitance can be set in four steps (50, 150, 300, and 400 pF), covering the majority of cartridges on the market. The low value of 50 pF is useful for compensating for the capacitance added by long or average-quality interconnect cables.

Six gain levels and MM/MC cartridge compatibility

Gain is switchable in six steps: 40, 45, 50, 55, 60, and 65 dB, with a 6 dB bonus on the XLR outputs. This fine segmentation (in 5 dB steps) offers a real advantage over the Phono Box S3 B, its little brother, which offers only four steps (40, 45, 60, and 65 dB) and imposes a 15 dB jump between MM and MC settings. The intermediate 50 and 55 dB values of the DS3 B make matching easier with medium-output MC cartridges or low-output moving iron (MI) cartridges, since the gain is not tied to a fixed MM or MC mode.

Two connected turntables, settings stored

The Phono Box DS3 B accepts two turntables simultaneously: one via the XLR inputs (standard XLR pair or 5-pin mini XLR), the other via the RCA inputs. A front-panel button allows switching from one input to the other. Settings (gain, impedance, capacitance) are stored individually for each input and recalled automatically when switching. This avoids having to reconfigure the device each time the turntable or cartridge is changed.

The stereo 5-pin mini XLR input is compatible with Pro-Ject’s “True Balanced Connection” cables. It carries both channels on a single connector with a separate ground connection. Any Pro-Ject turntable equipped with an RCA, mini XLR, or 5-pin output can be connected to the DS3 B.

Shielded construction and refined finishes

The steel chassis is covered with screwed-on aluminum panels (not clipped on), a construction that ensures mechanical rigidity and shielding against electromagnetic interference. This type of protection is all the more important because the high-gain discrete circuit is sensitive to stray fields. Pro-Ject recommends keeping the device away from the large transformers of power amplifiers, whose radiation can pass through the enclosure despite its thickness.

The external switching power supply (18 V / 500 mA) is placed outside the chassis to avoid any electromagnetic contamination of the audio circuit. Its standby power consumption is less than 0.5 W. To go further, Pro-Ject offers the optional linear power supply Power Box DS2 Sources, which uses a low core-saturation transformer with shielding between windings. This power supply, with dimensions comparable to the preamp itself, provides cleaner current and reduces the transformer’s mechanical micro-vibrations.

Magnetic wooden side panels are available separately in several finishes (walnut, eucalyptus, rosewood). They attach magnetically, without tools. The unit is available in silver or black finish.

Subsonic filter and trigger inputs/outputs

A front-panel switchable subsonic filter cuts frequencies below 20 Hz with an 18 dB-per-octave slope. This filter eliminates unwanted infrabass (turntable rumble, tonearm resonances, record warps) without affecting the audible band. It is useful with bass-reflex speakers or subwoofers sensitive to subsonic signals.

The trigger inputs and outputs (2.5 mm jack, 12 V) allow the DS3 B to be powered on in sync with another Pro-Ject Box device or a compatible amplifier. Turning on the turntable can trigger the preamp to power on, simplifying everyday use.

Technical specifications

Inputs

• Input connections
  • 1 5-pin mini XLR
  • 1 pair of XLR
  • 1 pair of RCA
• Input impedance: continuously variable from 10 to 1000 ohms, or fixed at 47 kOhms
• Input capacitance: 50, 150, 300, 400 pF
• Compatible with MM and MC cartridges
• Possibility to connect two turntables simultaneously, with settings stored for each input
• Settings accessible from the front panel

Amplification stage

• Fully balanced and discrete gain stage (new)
• Fully discrete audio circuitry, without operational amplifiers (new)
• Dual mono design
• Switchable gain: 40, 45, 50, 55, 60, 65 dB (+ 6 dB on the XLR output)
• Continuous impedance matching via potentiometer, Pro-Ject Audio Systems patented system allowing transparent adjustment during playback
• Extremely precise matching for MC cartridges

RIAA equalization

• Fully passive and discrete RIAA equalization (new)
• RIAA equalization accuracy: < 0.25 dB from 20 Hz to 20 kHz
• Subsonic filter: at 20 Hz with an 18 dB / octave slope
• Fully separate passive equalization for better impedance matching and minimal deviation from the ideal RIAA curve

Outputs

• Line output
  • 1 pair of RCA
  • 1 pair of XLR
• Balanced XLR inputs and outputs (new)
• Balanced 5-pin mini XLR input (new)
• XLR connector wiring: 1 ground, 2 “hot” (hot pin), 3 “cold” (cold pin)
• Discrete balanced output stage for XLR outputs
• Independent discrete output stage for RCA outputs, fed directly by the RIAA equalizer

Audio performance

• Signal-to-noise ratio MM (40 dB): 104 dBV, 111 dBV A-weighted
• Signal-to-noise ratio MC (60 dB): 85 dBV, 91 dBV A-weighted
• Total harmonic distortion at 1 kHz: < 0.001 % in MM, < 0.004 % in MC
• Total harmonic distortion (20 Hz - 20 kHz): < 0.005 % in MM, < 0.01 % in MC
• Low noise and low distortion

Power supply

• External power supply: 18 V / 500 mA DC
• Power consumption: 18 V / 290 mA DC maximum, < 0.5 W in standby
• Trigger input and output: 12 V on / off detector
• External switching power supply, compliant with legal requirements (guaranteed standby consumption of 0.1 W)
• Compatible with the optional linear power supply Power Box DS2 Sources for improved performance

Construction

• Steel chassis covered with screwed aluminum panels, ensuring excellent rigidity and effective insulation against interference
• Solid aluminum enclosure protecting against interference
• Magnetic wooden side panels available separately
• Available finishes: silver or black

Dimensions and weight

• Dimensions: 20.6 x 7.2 x 19.4 cm (19.5 cm with connectors)
• Weight: 1480 g without power supply