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Pro-Ject DAC Box RS: inputs and digital audio formats galore!

By Barry Moore |

Those of you Hi-Fi lovers who like DACs to have multiple inputs will be thrilled with the DAC Box RS by Pro-Ject. The device supports digital audio files of 24-bit at 192kHz, and even DSD64 and DSD128 files. Thanks to the array of settings and added extras, you can listen to music via the output amplifier on the transistor or the tube. Audiophiles, let's take a closer look!

The design of Pro-Ject?s DAC Box RS is very minimalist. This is characteristic of the Austrian manufacturer, indicating that we are dealing with a product from Pro-Ject?s high quality range.

This minimalist design is implemented both internally and externally. Indeed all the products from the RS Line have a very classy appearance, rivalling even the most expensive devices.

There are endless possibilities as the DAC Box RS contains nine digital inputs, including a USB B input. The device supports signals of up to 192kHz on 24-bit, as well as DSD64 and DSD128 signals.

The DAC also enables you to listen via a class A transistor stage, or via a tube stage, both in an asymmetric and symmetric mode.

Let?s take a closer look at this charming device.

About Pro-Ject?s DAC RS Box


The Pro-Ject DAC RS Box looks stunning, with a thick solid anodised aluminium frame and casing.

The switches, display and text are classically discreet, which is a characteristic feature of the manufacturer.

The power switch is located on the left with the LED light placed above it. The light remains illuminated when the Solid output is selected (transistors), flashes when you choose the tube stage, and signals when it has not yet reached its operating temperature.

The remote control receptor?s infra-red diode is located on the right of the switch. When the remote control is in the on position, it can pause (and of course re-start) the DAC Box RS.

In the middle of the front face there are two rows of LED lights on top of each other. Those on the top indicate the sampling frequency of 44 to 192kHz, and also DSD64 and DSD128 signals, whilst the LED lights on the bottom indicate the selected input, and are numbered 1-9.

A simple two-position switch enables you to access the inputs by scrolling up or down. It is located between two other inverters, the first offering the choice of filter 1 or filter 2, and the second between the transistor output and the lamp output.


The device has numerous digital inputs. Included are: an asynchronous USB B input to attach to a computer, an input labelled ?Sonic? used in conjunction with the output ?Clock? to attach to a CD Pro-Ject CD Box RS, a standard professional symmetrical AES/EBU output on a XLR socket, and six S/PDIF outputs, (two coaxial and four optical).

The stereo analogical signals remain at a fixed level in the asymmetric mode on Cinch sockets, and in a symmetric mode on the XLR sockets. These two different outputs do not have to be connected at the same time.

The power feed block socket is a XLR mini model with three interlocking connections (of which two are used).


The DAC Box RS?s manufacturing is very impressive. The internal frame is made up of steel sheets coated with black granite paint, and is surrounded by a base, a lid and two side faces which are partially joined. They are made of natural anodised aluminium with a thickness of 3mm.

The solid anodised aluminium frame of 10mm is mounted on an internal façade, providing the device with a firm stability.

The main card occupies the whole surface of the box, and receives six smaller cards attached via their solid connecters, whilst a different card contains the switches. The LED light is fixed onto the back face and is connected to the main card by layers of computer data.

Power feed and management

The device is powered by a 78M15 regulator and a voltage changeover switch, creating a negative power supply that uses the transistors Mosfet IRLR6225 and IRF9530NS. The latter serves as a controller to regulate the negative power supply.

A network of transistors (of the ULN2003 model) are used to feed the LED light on the front face, whilst the management of the electronics is ensured by an Atmel Atmega164PA micro controller.

USB Interface

The USB interface occupies a daughter card mounted on the main card. There is also a USB Microchip USB3318 receptor and a XMOS SK1220L1 processor, which samples the 12S and DSD signals.

The oscillators aimed at generating the synchronisation frequencies with digital audio fluxes at 44.1kHz and multiples, and 48kHz and multiples, are found on the other daughter card situated just behind.

The oscillators are the low-jitter configurable templates FoxElectronics XpressO. These offer a stability of + or ? 20ppm (parts per million, as in 20.10-6).

Digital analogue filter conversion

There are two Burr-Brown PCM1792 convertors (one per channel). These accept PCM signals of 24-bit at 192kHz, and are compatible with DSD signals, which ensure the digital analog conversion. They are found on the same daughter card that contains the oscillators.

The PCM1792 has differential current outputs. These are converted into voltages by the low-noise NE5534 operational amplifiers, which Pro-Ject also uses for combination filtering with resistances and condensers with plastic layers.

The filtered signals are then symmetrized by other low noise operational amplifiers of the NJM2068 model, manufactured by the New Japan Radio Company (JRC).

Thus the user can choose between the outputs and signals boosted by the lamp stages using the ECC88, or by the Mosfet IRF510S transistor stages of a class A Siliconix origin. The direct signals are available from the source, and the reverse phase signals are available from the drain of this IRF510S.


The Pro-Ject DAC Box RS offers a consistent audio reproduction, which is very clean, and slightly softened at the top end of the range. However the transistor output is a little more airy than the tube output.

When listening to various extracts from the album Gloria, Dixit Dominus by Vivaldi with Rinaldo Alessandrini directing the Concerto Italiano, the strings are incredibly smooth, and the bass and vocals are exquisite, sounding more majestic than ever.

In The Marriage of Figaro, where Pier Giorgio Morandi conducts the Hungarian State Opera Orchestra, Mozart?s opera is fantastically reproduced; the orchestra has a stronger presence whilst the soloists appear closer. Listening via the transistorised output appears better suited to masculine voices, whereas feminine voices sound better via the tube stage.

This strong restitution gives Stromae?s album Racine Carrée an impressive unfaltering richness?the Belgian artist does not need to change anything. In particular, the song Merci makes you catch your breath.

In DSD, the Divertimenti and the Simple Symphony by Britten played by the Trondheim Solistene (test file no.21/hires), has particularly ?piercing chords, that slowly increase in warmth when played via the DAC Box EQ. However the folk track Show me the Way by Anne & Pete Sibley very smoothly reproduces its sweet melody.

In conclusion, the DAC Bow RS is a very seriously designed device, whose numerous inputs and ways of reading of audio digital files are extremely useful, whether listening on a tube or on a transistor. In both cases, be careful, as the amazing sound restitution can be extremely addictive!

User Manual
Pro-Ject Website
Audio Marketing Services (importateur)

Reading capabilities

Pro-Ject DAC Box RS


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