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Grimm Audio UC1

Audio Interface, A‑D/D-A Converter & Monitor Controller By Hugh Robjohns
Published June 2022

Grimm Audio UC1

There are many high‑end converters that boast excellent specifications — but this one sounds good too!

Based in the Netherlands, Grimm Audio have been manufacturing high‑end professional and consumer audio products for almost 20 years. They make a very eclectic range of products, including converters, master clocks, music streamers and high‑end active loudspeakers, along with cables, replacement vintage valve mic power‑supplies, and even loudness metering plug‑ins. What they have in common is the company’s approach: Grimm are very engineering and science led, and often employ unusual technical solutions.

Over the years, Grimm Audio have produced several digital converter systems, but the only one in their current product catalogue is the UC1, which they describe as a Universal Converter. As you’d expect from the asking price, it’s very much aimed at professional mixing and mastering applications, but particularly at those using either Grimm Audio’s own LS1 active monitor speakers or PMC’s professional active monitors, which can be connected using bespoke digital audio‑plus‑control interfaces on RJ45 sockets.


At its heart, the UC1 is a 20‑channel (10x10) line‑level USB interface (there are no mic preamps) with integrated monitor control functions. Housed in a 1U rackmount chassis extending about 210mm behind the rack ears, it is an elegant‑looking device with a rich padauk (tropical hardwood) front panel. Set into this joinery is a small colour display which shows I/O signal levels, the selected monitoring source, the current volume setting, and the prevailing sample rate. The same display is also used to navigate the configuration menus, controlled through a rotary encoder and a couple of soft buttons.

Also set into the woodwork are two quarter‑inch TRS jack sockets, providing a powerful headphone output and an unbalanced stereo analogue input; both have volume controls. A second USB connection called the ‘i‑put’ is intended for stereo USB sources like a laptop or smart device. Although there are no mic preamps, the unbalanced input can accept instrument sources, as it presents a 1MΩ input impedance!

The rear panel is absolutely crammed with socketry, starting with a universal IEC mains inlet with an integrated on/off switch, accepting 90‑240 V AC. A power LED sits as the dot above the ‘i’ of ‘Grimm’ on the front panel. There’s a 3.5mm remote‑control socket, too, although this facility hadn’t yet been implemented at the time of writing. Audio connectivity is arranged with digital I/O to the left and analogue I/O across the middle, all on XLRs.

Ten physical inputs can be routed to a DAW over the primary USB port on the rear panel. These inputs comprise two rear‑panel balanced XLRs, two front‑panel unbalanced inputs on a quarter‑inch stereo TRS socket, four digital inputs on two more AES3 XLRs, plus the i‑put USB stereo input on the front‑panel.

On the output side, a DAW can send 10 separate output signals into the UC1 over the primary USB connection. General purpose outputs comprise four analogue balanced XLRs and one AES3 stereo digital XLR output, so there’s sufficient analogue and digital connectivity to connect a piece of outboard hardware (a compressor, for example) and to route signals to and from the DAW, which is what the handbook references to ‘loop’ connections are all about.

The LS1 control out port is compatible with PMC’s active monitor speaker interface.The LS1 control out port is compatible with PMC’s active monitor speaker interface.

Another pair of analogue balanced XLRs is intended for a secondary monitor speaker pair but can also be allocated as artist cue outputs. The front‑panel headphone output always duplicates the signal being sent to these outputs. The powerful headphone amp is designed to work well with higher‑impedance headphones (up to 30mW into 600Ω).

The main (bespoke digital) stereo speaker outputs appear by default on an Ethercon‑style RJ45 connector, but this connection is not Ethernet and isn’t compatible with any of the common AoIP formats. Instead, it carries a proprietary combination of AES3 audio and MIDI control data for Grimm Audio’s own LS1 digital speaker system — the data element controlling volume and muting functions directly in the monitor speaker.

However, a menu function allows the data format at this connection to be configured to PMC’s own proprietary digital speaker interface standard, extending the UC1’s application and versatility considerably. And if Grimm Audio LS1 or PMC active speaker systems aren’t available, the main monitor speaker signal can be routed internally to either the first two analogue or the AES3 digital outputs instead, with volume and muting etc performed inside the UC1.

All analogue outputs operate with a nominal level of +4dBu, which equates to a digital signal level of ‑14dBFS, corresponding to the standard EBU alignment (0dBFS = +18dBu). As shipped from the factory, the same alignment also applies to the analogue inputs, although a menu option recalibrates the A‑Ds to accept +24dBu, if...

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