PreSonus Quantum HD8

With their latest Quantum interfaces, PreSonus have swapped Thunderbolt for USB. Do they still maintain the same advantages?

When PreSonus first attached the name Quantum to a 1U audio interface, it was not short of unique selling points. Back in 2017, Quantums (or should that be Quanta?) connected to the host computer over Thunderbolt, and took full advantage of that protocol’s special powers. So much so, in fact, that even eight years later, the Thunderbolt Quantum interfaces are still unmatched for low‑latency performance, and nothing since has come close to the Quantum 4848 for huge I/O counts on a project‑studio budget. When the time came to refresh the Quantum range last year, however, PreSonus nevertheless gave up these advantages, switching to USB connectivity in pursuit of wider compatibility and lower cost.

There are obvious parallels here to what Focusrite have done with the Clarett range. In the first generation of Thunderbolt Clarett interfaces, the focus was on low‑latency performance; but when the Clarett+ refresh took place in 2021, Thunderbolt was dropped, and the current models are now all USB. Clarett+ became the ‘premium’ alternative to Focusrite’s bestselling Scarlett line, offering additional features and better specs rather than a fundamentally different platform. PreSonus’ move with the Quantum interfaces looks very similar, positioning them as upmarket alternatives to their Studio C range. So, what do the USB Quantums offer that’s special, and why should you buy one of these rather than its cheaper Studio C counterpart?

Four Front

There is a total of four models in the USB Quantum range (and the Thunderbolt Quantum 2626 is still a current product, too). The ES2 and ES4 occupy a wedge‑shaped, desktop form factor, whilst the HD2 and HD8 are 1U half‑ and full‑rack devices respectively. PreSonus sent all four models for review: I’ll focus mainly on the flagship HD8 and note any relevant differences where applicable. Build quality throughout the range is reassuringly robust, with stout metal shells and chunky faceplates to the fore. Everything is finished in a smart and businesslike black, though some of the legending on the rackmount models is quite small and hard to read at a distance.

All four models use a new mic preamp design dubbed 'Max‑HD', and I can’t discover any feature with the initials ES, so the thinking behind PreSonus’ naming conventions is a little obscure. The main functional differences are as follows. The ES models are USB powered, whilst the HD2 requires an external DC supply and the HD8 accepts an IEC mains cable. The ES variants have mini‑jack MIDI in and out, whilst the HD Quantums have a DB9 connector for a flying cable assembly that also features coaxial S/PDIF in and out. Both HD models can access up to 16 channels of ADAT Lightpipe digital I/O on two pairs of optical Toslink connectors; the HD8 also has word clock in and out, whilst the ES units offer no digital audio expansion. Worthy of note, the HD8 can also be used without a computer connection as a standalone ADAT expander.

The HD8 back panel includes an IEC power input, optical ports, a breakout port for MIDI and S/PDIF sockets, eight quarter‑inch line outputs, a pair of main outputs, and eight combi jack/XLR audio inputs.

On the analogue front, the ES2 and HD2 both have two mic/line inputs on combi XLR/jack sockets, while the ES4 has four and the HD8 eight. The first input on the ES2 and the first pair on the others also have dedicated high‑impedance jack sockets on the front panel, which override the rear‑panel combi sockets when a guitar or bass is plugged in. These are complemented on the HD models by the intriguing addition of a pair of front‑panel jack outputs specifically designed for re‑amping. The remaining analogue outputs are all on balanced jacks, of which the ES2 has two, the HD2 and ES4 four, and the HD8 no fewer than 10.

Universal Credit

It’s obvious from the moment you power up one of the new Quantums that PreSonus have gone all‑in on digital control. There is nary an analogue pot, button or switch to be found anywhere. Preamps, cue mixing, monitor control, metering and even headphone level are set digitally, using a single master rotary encoder. This delivers visual feedback using a ring of coloured LEDs, and has a push action to confirm parameter settings. It is accompanied by a small but detailed colour display, which does multiple duty as a meterbridge, numerical readout and so...