NuPrime DAC-9X

Hitherto better known in hi‑fi circles, NuPrime make converters of a quality that could appeal to pro audio users.

American company NuPrime are probably better known in the hi‑fi market than in pro‑audio circles, but their lineage dates back to 2005 in the form of a company called NuForce that was founded by Jason Lim, a man whose previous career path involved designing microprocessors and Internet technologies for the likes of Motorola, Sun Microsystems, Oracle and others. Lim served as the CEO of NuForce for eight years, during which time the company became a leading light in Class‑D amplifier technology, amongst other things. In 2014 he founded NuPrime, which acquired the high‑end audio division of NuForce and started creating high‑quality products for the hi‑fi, home‑theatre and gaming markets. In their second year, NuPrime won four Product of the Year awards, and they’ve gathered many more accolades since.

The company currently make seven different D‑A converter (DAC) products, but the NuPrime DAC‑9X has been designed specifically for “studio professionals”, which is why this one has made its way to us at SOS for review. In essence, it’s a reference‑grade DAC with a variety of digital and analogue inputs and outputs, plus a standard quarter‑inch stereo headphone output. So it could conceivably serve in the studio or on location as a straight stereo D‑A converter, a source selector and preamp, and as a headphone amplifier.

Technology

Unusually, NuPrime’s DAC‑9X is built with a dual‑mono signal path, based around a pair of ESS Sabre ES9028Q2M digital‑to‑analogue converter chips. The 9028Q2M is a very high‑performance stereo D‑A converter that uses the manufacturer’s highly‑regarded 32‑bit Hyperstream technology, which is potentially capable of delivering a dynamic range of up to 129dB. It supports PCM sample rates up to 384kHz, as well as the DSD format up to DSD512 (22.6MHz). Although designed as a stereo D‑A converter chip, it can be configured as a mono converter, with the two channels working together in a balanced configuration. This arrangement provides a further 3dB improvement in the noise performance, and is how and presumably why it is being used here — hence there being two of them. The ESS converter includes a variety of onboard DSP functions for different reconstruction filter responses, de‑emphasis filtering, and volume control, but none are available to the end user; all are preset in the DAC‑9X by the manufacturer.

Inside the box, the conversion is based around a pair of ESS Sabre ES9028Q2M chips.

Separately, additional DSP functionality (courtesy of an XMOS processor) recognises and decodes MQA‑formatted audio files (for more on MQA see our SOS August 2016 article: https://sosm.ag/mqa-format), as well as supporting DSD‑encoded audio via either the ASIO 2.1 (over USB) or DoP (DSD Over PCM) formats. Although there is a digital volume control included within the D‑A converter chips, NuPrime have chosen to use a separate, digitally controlled, 99‑step analogue switched resistor network for the DAC‑9X, to avoid noise and distortion artefacts.

Internal construction is to a high standard, with the toroidal transformer and power regulators towards the front of the unit, and all the converter, analogue output and control circuitry on a large circuit board at the rear of the unit, constructed using SMD components.

Connections

All connections except for the front‑panel headphone socket are at the rear, starting with an IEC mains inlet with integral power on/off switch. The voltage markings on the rear panel might be mistaken as suggesting that a universal switch‑mode power supply is employed here, but that’s actually not the case. The DAC‑9X contains a traditional linear power supply, which means the mains voltage (100‑130 or 200‑240 Volts AC) must be selected manually. Due to the limited rear‑panel space NuPrime have placed the voltage selector on the bottom of the case and put the mains fuse inside, in an in‑line fuse holder on the mains wiring to the transformer. I’m told that all units are shipped with the switch set in the 230V position (which prevents inadvertent damage whatever territory you’re in) and that new units have a sticker to indicate the factory‑set voltage. Ideally, though, I’d prefer a more permanent explicit warning on the rear panel or lid near the IEC inlet (stickers are easily removed, as on this review unit), and for this power‑supply voltage arrangement to be given greater prominence in the user manual (currently, it isn’t mentioned until page 17 of 22).

Analogue outputs are provided on pairs of balanced XLRs and unbalanced RCA phono sockets, with maximum output levels of +20.1dBu at the XLRs and 6dB lower (4V RMS) for the unbalanced output — although it should be noted that this is an unusually ‘hot’ unbalanced signal. There are two further outputs. First, there’s an optical S/PDIF output which appears to provide a loop‑through of the selected digital input, with limited format support (only PCM rates up to 192kHz and DSD64; the user manual provides no other information). Second, there’s a 12V Trigger output for switching associated equipment on/off.

The DAC‑9X features a range of analogue and digital input options, including up to 24‑bit 384kHz PCM support over USB, but lacks direct support for some common professional formats such as AES3.

On the input side, a pair of RCA phono sockets accept an unbalanced analogue stereo input (maximum 1V RMS, +2dBu, 0dBV). Two S/PDIF digital inputs are catered for, in coaxial form via another RCA phono socket, and in optical form via the usual TOSlink port. A USB 2.0 B‑type (square) socket accepts audio data from a computer (or NAS) in the usual way (a Windows Driver is available on the company’s website). There’s also a USB A‑type socket on the rear panel, but this one is non‑standard, and intended for the exclusive use of NuPrime’s optional Omnia WR‑1, BTR‑HD, Stream Mini, or Stream Mini DAC Bluetooth and Wi‑Fi streamer hardware. Another entirely proprietary connection format employs a pair of HDMI sockets that accept I2S and DSD data streams in a bespoke format used by NuPrime’s own CD transports and streamers — these are not compatible with standard HDMI video sources.

As might be expected, these different digital connections have different capabilities in terms of the maximum digital resolution they support. For example, the USB2.0 interface supports PCM data up to 384kHz and 24‑bit from all computer platforms. Mac and Linux machines can also convey DSD64 or DSD128 via the DoP format, while Windows machines go further up to native DSD256, using the ASIO format.

The two I2S inputs have the greatest capability, supporting 32‑bit audio data with sample rates up to 384kHz, as well as DSD formats up to DSD256. The coaxial S/PDIF input supports PCM up to 384kHz/24‑bit and DSD DoP 64 and 128 formats, while the optical S/PDIF input (and optical output) can only manage PCM up to 192kHz/24‑bit and DoP 64. And finally, the proprietary USB‑A socket for streaming extensions only accepts PCM data up to 192kHz/24‑bit.

Controls

The DAC‑9X’s front panel is pleasingly simple, with two rotary encoders on the outer edges. A quarter‑inch headphone socket, a miniature toggle switch, and a pin‑prick LED display (plus remote‑control IR receiver) occupy the centre of the panel. Both rotary controls have press functions. On the left knob this activates the unit or puts it into a standby mode when held for three seconds, while rotating the knob selects input sources, which are displayed as a two‑character code on the LED matrix (C1 for coax S/PDIF, for example).

The display can be switched to show the current sample rate (44.1 up to 384 kHz for PCM formats and a choice of 64, 128 or 256 DSD formats). A miniature LED hidden in the Q of the MQA logo changes colour to indicate different MQA modes, with magenta indicating the MQA ‘original sample rate’ (ORFS) format, blue for the MQA Studio and green for MQA Authentic formats. Yellow is shown for DSD.

A toggle switch on the front allows the output level to be fixed (at maximum volume) or variable, set using the right‑hand rotary encoder, with the current volume indicated on the LED display (between 00 and 99, each step being 0.5dB). Pressing the volume knob mutes the output, and when unmuted the level ramps up over a few seconds to avoid surprises.

If the volume control is switched to the ‘fixed level’ mode the headphones remain muted, which is a sensible safety‑conscious feature.

Plugging headphones into the front‑panel socket automatically mutes the rear‑panel outputs, but if the volume control is switched to the ‘fixed level’ mode the headphones remain muted, which is a sensible safety‑conscious feature. I was slightly surprised that there is no provision here for ‘balanced’ headphones, which is rapidly becoming a ‘standard’ feature these days, even in professional circles. The maximum headphone power is obviously dependent on the headphone impedance, but ranges between 1700mW for 32Ω and 135mW for 600Ω. I tried a selection of headphones, including the Sony MDR‑7509 (24Ω, 107dB/mW), AKG K702 (62Ω, 94dB/mW) and Sennheiser HD600 (300Ω, 98dB/mW), and all were able to deliver far more volume than I’d ever need.

A small handheld IR remote control is included with dedicated buttons at the top to switch between on/standby, and to change the display mode. A ‘ring dial’ controls the volume, cycles through the inputs, and mutes the outputs. Alternatively, a quincunx of buttons allows the first five sources to be selected directly, but as the two I2S inputs (H1, H2) don’t have dedicated buttons of their own, the analogue input (A5) button has to be pressed repeatedly to cycle around the A5, H1 and H2 sources.

Test Bench Results

I performed my usual range of technical measurements on the DAC‑9X using an Audio Precision test set. Most measurements agreed with the published specifications, although the best THD+N figure I achieved was only 0.00075% instead of the claimed 0.0005%. Balancing that bitter disappointment [for comically daft legal reasons, SOS would like to stress that those words constitute a joke! — Ed.], the published signal‑to‑noise ratio is 110dB, whereas my measured was nearly twice as good at 115dB (or 119dB A‑weighted). Similarly, the specs give a ±0.3dB tolerance for the frequency response, but I found it flat within ‑0.1dB from 4Hz to 22kHz, dipping to just below ‑6dB at the Nyquist limit (at 48kHz sample rate).

Regular readers will know that my favoured DAC ‘overall quality check’ indicator is the AES17 dynamic range measurement — to achieve the best scores, every facet of a product’s design, including the power supply, needs to be exemplary — and that delivered a result of 120.5dB A‑weighted. This performance ranks the DAC‑9X in ninth position in the league table of converters that I have personally bench‑tested, equalling the original Lynx Hilo’s score, and sitting between the RME AIO‑Pro PCIe card interface and the Cranborne Audio 500 R8 rack interface. Although it doesn’t quite attain what the converter chip manufacturers claim is possible, this is still an impressive performance that is comfortably of high‑end professional mastering quality.

Prime Time?

Given the number of proprietary digital input connections used and that there’s no explicit support for AES3 at all (the coaxial S/PDIF input will accept AES3 data, of course), the ‘designed for studio professionals’ claim is perhaps a bit of a stretch, but I have no qualms about the quality of conversion on offer: the DAC‑9X is an impressive product that achieves a very high technical standard and delivers useful facilities. It is nicely constructed, looks elegant, is easy to use, works well, and boasts a powerful headphone amplifier and balanced analogue outputs operating at (European) professional levels.