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Yellowtec PUC2 USB 2 Audio Interface

USB Audio Interface For Mac & PC By Hugh Robjohns
Published July 2014

Yellowtec PUC2  USB 2 Audio Interface

Yellowtec make lots of equipment for the broadcast market, but their latest interfaces could be just the ticket for music production.

Yellowtec is a marketing brand of the German company Thum+Mahr, who are major broadcast systems integrators. Consequently, Yellowtec equipment is a familiar sight in the broadcast world, but it's less common in music production circles. The product range is unusually eclectic, including display‑screen mounting brackets and arms, mic and lighting support arms, studio status‑light systems, telephone and ISDN hybrids, microphones with built‑in solid‑state recorders, digital self‑op broadcast mixers, and USB audio interfaces.

The PUC2 is a compact, two‑channel, USB 2 bus‑powered audio interface, and there are three versions: in addition to the Standard model, reviewed here, a 'Lite' version omits the analogue interfacing, and a 'Mic' version accepts either mic or line inputs and a stereo headphone socket replaces the line outputs. At the heart of all models is a Cirrus Logic CS4272 codec chip, providing two‑channel A‑D and D‑A conversion, with 24-bits and up to 192kHz sample rates. Another, now-discontinued model (which may still be available from some resellers), the PUC Classic, is limited to a 48kHz maximum sample rate.

All versions are housed in an extruded aluminium case (127 x 42 x 185 mm) weighing around 600g. It's a modular design with each version employing different analogue I/O boards internally, and different end panels externally. The computer connection panel features AES3 inputs and outputs on XLRs, along with a USB (B‑type) port and a yellow‑ringed 3.5mm socket (and associated LED), which is used to configure the zero‑latency monitoring modes. The standard PUC2 version also has a 3.5mm aux output socket on this panel, which can be used for emergency headphone monitoring — although there's no level control.

The zero‑latency monitor (ZLM) feature allows input signals to be auditioned directly, and to be blended with the signal from the computer, if required. Signal mixing is performed in the digital domain,so the converter delays (under 5ms) remain, but the USB conversion and computer OS latency are bypassed completely. The ZLM mode is activated by connecting the tip and sleeve contacts on the yellow ZLM socket. The computer and input signals are attenuated by 6dB to avoid overloading the output stages, by default, but this can be over‑ridden by connecting the tip, ring and sleeve contacts on the ZLM switch jack instead.

A custom B‑type to dual A‑type USB cable is provided, as the PUC apparently requires more current than some single USB sockets can provide. The second (yellow) USB A plug only gathers additional power, and a status LED alongside the USB port indicates when the unit is adequately powered and recognised by the host computer. Yellowtec designed the PUC2 interface to work as a native plug‑and‑play device with all Windows (XP/Vista, Win 7) and OS 9 and later Macs, but a version of the familiar 'Ploytec' ASIO driver (32‑ and 64‑bit) is also available for more sophisticated applications. A firmware updating tool is also available.

The connectivity at the other end varies with model. The standard PUC2 has four XLRs for balanced stereo line‑level analogue in and out, while the Mic version has two combi‑XLRs for mic- and line‑level inputs, plus a quarter‑inch stereo headphone output socket, and the Lite version has a blank panel. The Classic is fitted with a D‑sub connector for compatibility with common broadcast interfaces.

In the PUC2 Standard and Mic models, detection of a valid AES3 input automatically favours that over the analogue inputs, but both analogue and digital outputs are active at all times. The preamp gain of the Mic version is controlled by faders in a bespoke software application, with the lowest mic input level for a full‑scale digital output being ‑62dBu, and the highest ‑8dBu. The software provides output-level metering, global phantom power, individual high‑pass filters and polarity inversions, and panning, for the inputs, across the two output channels, along with an output monitor mixer and headphone volume control. The line input gain (via the TRS socket within the Combi‑XLR) can also be adjusted with the faders, accepting +18dBu at maximum and ‑37dBu at minimum (for a full-scale output).

Analogue line‑level interfacing in the standard PUC2 version is configured for the German broadcast standard, which employs a +6dBu nominal operating level with +15dBu maximum peaks. However, an alternative model, optimised for a +4dBu operating level and +18dBu peaks (EBU standard), is available on request. The line input impedance is 18kΩ, and the A‑weighted AES17 dynamic range figures, measured using an Audio Precision test set, are 107dBA for the D‑A, and 109dBA for the A‑D — which is a respectable performance for the money, but around 14dB below the current high‑end target. Distortion is of the order of 0.0006 percent (THD+N, A‑weighted) for the A‑D, and slightly higher for the D‑A, while the frequency response extends to 5Hz (‑3dB) at the low end, with a subtle downward tilt below 100Hz, reaching ‑0.5dB at 20Hz. The high‑end roll‑off is determined by the sample rate, of course.

Overall, the PUC2 family of converters represent very good value for money, providing well thought‑out features and delivering good-quality audio in each direction in a no‑nonsense, reliable package. The ASIO drivers proved stable, and the Mic control application is versatile and very easy to use. Hugh Robjohns

PUC2 (German or international levels) £456; PUC2 Mic £618; PUC2 Lite £348. Prices include VAT.

PUC2 (German or international levels) $595 each; PUC2 Mic $795; PUC 2 Lite $455.