Two ESS9038Q2M converters in dual-mono, PCM to 768kHz, DSD512, full hardware MQA decoding, a headphone amplifier and a variable output — a complete digital front end in a box 103mm wide. The Pre Box S2 Digital is a digital-to-analogue converter, a headphone amplifier and a line preamplifier in one small enclosure. It takes USB, coaxial S/PDIF and optical inputs, and puts out a variable line level on RCA plus a 6.3mm headphone jack on the front. With a variable output it can drive a power amplifier or a pair of active speakers directly, without a preamplifier in between. The conversion is done by two ESS9038Q2M chips run in dual-mono, one per channel, which is an unusual amount of silicon for the size and price. Over USB it will take PCM up to 32-bit/768kHz and DSD up to DSD512 — DoP for the lower DSD rates and native at DSD512. The optical and coaxial inputs top out at 24-bit/192kHz, which is a limit of those interfaces rather than of the converter. MQA is decoded in hardware. There is a bank of selectable digital filters on the front panel, adjusted with the same knob that sets volume, and a full-colour OLED display that shows the incoming sample rate and the level. Published figures include 124dB of dynamic range, 0.0003% distortion at 2V RMS, and 100 femtoseconds of jitter. One important correction, because this product is routinely mis-shelved: the Pre Box S2 Digital is not a network streamer. It has no Ethernet port, no Wi-Fi, no Bluetooth and no app. Every input is a wire. If you want a streamer you want Pro-Ject’s Stream Box S2 Ultra or Pre Box RS2 Digital, and the Pre Box S2 Digital would sit downstream of one. Used with a computer, a CD transport or a streamer as its source, it is superb; used on its own it will not fetch anything from your network. Two published figures disagree between Pro-Ject’s own documents and we are flagging both rather than picking. Their web page says seven selectable filters; their PDF datasheet says eight. Their web page gives the supplied power supply as 5V/1A while the PDF states only 5V over micro-USB with no current figure at all. Features Two ESS9038Q2M 32-bit converters in dual-mono, one per channel PCM to 32-bit/768kHz and DSD to DSD512 over USB Full hardware MQA decoding USB B, coaxial S/PDIF and optical TOSLink inputs Variable RCA output — can drive a power amplifier or active speakers directly 6.3mm headphone output on the front panel, 68mW into 32Ω Selectable digital filters and a full-colour OLED display Not a streamer — no network, Wi-Fi, Bluetooth or app Specifications Type: Digital-to-analogue converter, headphone amplifier and line preamplifier Network streaming: None. This unit has no Ethernet, no Wi-Fi, no Bluetooth and no companion app. Every input is a physical digital cable Converter: 2 x ESS9038Q2M, 32-bit, dual-mono PCM sample rates: 32 / 44.1 / 48 / 88.2 / 96 / 176.4 / 192 / 352.8 / 384 / 768kHz. USB carries up to 32-bit/768kHz; optical and coaxial are limited to 24-bit/192kHz DSD support: DSD64, DSD128, DSD256 and DSD512. DoP for DSD64 to DSD256, native at DSD512 MQA: Full hardware unfolding and decoding. One Pro-Ject source specifies this as being over USB only while the PDF datasheet does not restrict it — if MQA over coax or optical matters to you, ask us before ordering Digital inputs: 1 x USB B, 1 x coaxial S/PDIF (RCA), 1 x optical TOSLink. No analogue input Analogue outputs: 1 pair variable RCA line out, plus a 6.3mm headphone jack on the front Headphone output: 68mW into 32Ω. Pro-Ject’s web page adds 6.6mW into 600Ω and an 8Ω minimum load; the PDF does not repeat the 600Ω figure Filter options: Pro-Ject’s web page says seven selectable filters plus a proprietary optimum-transient filter; the PDF datasheet says eight. The two do not agree Volume control: Front knob with a full-colour OLED level readout. Pro-Ject does not state whether the volume stage works in the analogue or the digital domain Frequency response: 20Hz–20kHz THD: 0.0003% at 0dB, 2V RMS, 1kHz Dynamic range: 124dBA Jitter: 100 femtoseconds Output voltage: 2.05V effective Power supply: 5V over micro-USB. Pro-Ject’s web page states 5V/1A supplied; their PDF gives the voltage and connector only, with no current rating Dimensions: 103 x 37 x 122 mm (W x H x D), including the knob and connectors Weight: 366g without the power supply Country of manufacture: Not published for this product 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.
