Interphase Audio EQ Modules

Compatible with both the 500‑series and the 51X modular formats, these classy Allan Bradford‑designed modules offer up analogue magic in spades.

Towards the end of 2017, Bruno Wynants, founder/owner of Belgium‑based Interphase Audio, and gear designer Allan Bradford, visited us at SOS Towers to demonstrate their new Ark modular analogue console, a headline feature of which is its ability to host 500‑series modules in line with its own channels. We found ourselves impressed, and Technical Editor Hugh Robjohns remarked that: “It appears to be a very well‑conceived and beautifully engineered console, designed with considerable flexibility in mind. The set of modules available at launch is equally impressive and should meet the needs of most clients, but there are advanced plans for additional future options.”

Interphase have managed to sell and install several consoles in a range of different configurations since then, despite the logistical difficulties presented by the pandemic, and have recently started to deliver on their promise of new modules. The first trio, reviewed here, are all equalisers, and there are plans in place to follow these up with a mic preamp and an intriguing multi‑type analogue compressor, amongst other things.

Overview

As shipped, the module’s rear card connector is compatible with 500‑series racks, but Interphase Audio can also provide a clip‑on adaptor to take advantage of the 51X format’s higher‑voltage power rails.

As supplied, the three EQs, named the Iridium, the Carbon and the Helium, come ready to plug into any 500‑series chassis but, unlike most such modules, they aren’t limited to use in 500‑series racks: a small adaptor can be fitted onto the rear to provide the additional connectors required by 51X racks. Popular in the pro‑audio DIY community, the 51X format augments the usual 500‑series connections, adding ±24V power rails, which allow module designers to develop products with greater headroom — they can accept and output higher‑level signals. It’s perhaps not a surprise to learn, then, that one of the other products in the Interphase pipeline is a chassis capable of hosting 500‑series and/or 51X modules; to date I’ve only seen these as DIY projects or built on a very small scale.

All three of these modules are fully discrete Class‑A devices, whose beating heart is Allan Bradford’s Top Amp, a low‑noise, low‑distortion discrete op‑amp that he developed specifically to be more compact and better suited to mass‑manufacture techniques than the other boutique options out there. He tells me his design is guided by the ‘wire with gain’ ideal and that, in developing the Top Amp, he conducted extensive listening tests of a range of op‑amps, both IC‑based and boutique discrete; he says that on good speakers it’s possible to discern a significant difference between them. The chief practical benefits of his compact low‑noise design are that it can be manufactured at scale (great for building mixing consoles!), and it’s easy to accommodate several of them in small devices, such as these modules.

The review units were all very nicely constructed, exhibiting a solid feel and a slick finish. The circuit boards are populated with high‑quality components, of course, and are surrounded by a folded metal case with a small slot at the rear to allow the card connector through. Considering the number of knobs on the front plate, I was pleased with the amount of space available, and never felt as though my fingers would accidentally move an adjacent control. The aesthetic is pleasing to the eye too — very ‘hi‑fi’. That said, while the legends are clean and clear, the small black‑on‑grey typeface could make it tricky to read everything in a dimly lit studio, and when the units are placed below eye height much of the information is obscured by the tall knobs and their shadows.

Three...