Phaedrus Audio SHUpHLER MkIV

The imaging of stereo mic arrays and loudspeaker monitoring is not as accurate as it should be — and the SHUpHLER MkIV aims to address that.

The SHUpHLER ['shuffler'] is manufactured by small British company Phaedrus Audio, and I reviewed the original model back in SOS July 2017 (https://sosm.ag/phaedrus-audio-shuphler). The product has continued to evolve in important ways over the last decade, and I thought the latest Mark IV model had sufficiently improved, that this device warranted a second look. I’ll concentrate mainly on the changes and updates here, so if you’d like more information on the background to the shuffling processes please refer to my original review (which is free to view).

Same... But Different!

As you’d expect, the MkIV performs essentially the same job as the original — it provides a variety of shuffling configurations optimised for different stereo recording and listening scenarios. Importantly, though, two of its shuffling functions are completely new, and the audio connectivity has been enhanced too.

Like the original, the SHUpHLER MkIV is housed in a deep extruded aluminium case. It measures 108 x 46 x 225mm (WHD), but instead of the hexagonal anodised metal front panel of the earlier design, the new model employs thick fibreglass PCB end panels. The original anodised metal panels required additional processing to ensure they were grounding effectively against the case. Phaedrus subsequently discovered that this new double copper-clad PCB solution is a lot better in that respect. As the panels have relatively small dimensions and are quite thick, they are easily robust enough to support the control knob and I/O connectors, and I had no issues with interference despite heavy provocation!

The rear panel, showing the TRS balanced/unbalanced audio socketry and USB‑C power input.

Originally, the pro version of the SHUpHLER used a valve gain stage, but the latest model is entirely solid‑state, using a handful of Texas OPA2320 precision low‑noise, low‑power, CMOS op‑amps. It’s designed to operate on a single‑sided 5V power supply, a benefit of which is that it allows the SHUpHLER mkIV to be powered directly from any standard USB supply, via a USB‑C socket on the rear panel (a USB‑C to USB‑A cable is included). As the unit only draws 100mA of current, it will work with all USB 1.1, 2.0 or 3.x outlets, but ideally a good quality dedicated USB power supply should be used, to realise the unit’s impressively low noise‑floor specifications of ‑100dBu (A‑weighted).

The MkIV SHUpHLER is available in two versions: a professional transformer‑coupled balanced I/O model, and an unbalanced consumer version. Both have four quarter‑inch jack sockets for line‑level connections in and out. Being directly USB powered, the 5V power rail restricts the maximum internal signal level to just +7dBu or +5dBV, and so that’s also the maximum I/O level for the unbalanced version. The pro model’s balancing transformers not only provide galvanic isolation to avoid ground loops; they also step down/up the I/O levels with a maximum of +18dBu (giving a potential dynamic range of 118dB).

A view of the internal circuitry of the SHUpHLER showing the input and output transformers at the left next to the audio connectors, and the active shuffling circuitry to the right with the rotary selector switch on the vertical board.

The unbalanced transformerless model’s THD measurement is better than 0.001% at all frequencies, but the transformers in...