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The ISA One is built to last.

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The ISA One is a single-channel mic preamp (the name's a giveaway, right?). But strangely enough, there's also a separate DI input with its own gain.

As both inputs have their own outputs (XLRs on the back) if you're recording one mic and one DI, the ISA One is effectively a twin input stage. The other big news feature is a built in 'Cue Mix' option.

Now, the ISA One isn't an audio interface, so we're not talking about a complex software-driven system here. However, the front panel phones output points to some form of latency-free monitoring, on which more later.

Focusrite gear always includes plenty of options, and the ISA One is no exception. Top of the list has to be the flexible mic pre, which includes four input impedances (including the original ISA 110 option), phase reverse, high-pass filter and up to 80dB of gain. You'll also find the instrument input includes two impedance options and a DI box-style 'thru' output (labelled as 'amp').

The general layout and metering (including the rather nice VU meter) is also in line with Focusrite's more expensive ISA units.

A look round the back reveals plenty of connectivity, with all main ins and outs available on XLRs, plus balanced TRS jacks for everything else. There are individual send and returns for the insert (rather than the unbalanced single jack option you often see), left and right inputs for the cue mix, a standard TRS line input and an external input for the second channel.

From a technical perspective the ISA One ticks many of the same boxes as other ISA units. The transformer-based mic pre is the same Rupert Neve design found in the original 1980s desk design. Its Lundahl L1538 transformer combined with a bespoke zobel network and massive frequency bandwidth results in a mic pre that's both transparent and warm.

The optional AD card is the same one used in the top of the range ISA 430II. This adds back panel connectors for optical S/PDIF and word clock, with S/PDIF and AES connectors on a 9-pin breakout cable.

Routing

To get the most out of the ISA One it's worth taking a little time to understand the signal flow. In addition to the headphone option, we were particularly interested to see how the two separate inputs worked both on their own and in combination with the AD card.

The main mic input is pretty obvious, feeding its own XLR output, channel one of the AD and the main VU meter.

However, using the main input selector you can bring it up the main channel to use the insert point. At this point it also feeds the main VU and LED meter (as well as channel 1 of the AD and the main XLR out). Plugging into the external input jack on the back steals the second channel AD and output from the DI.

The ISA One addresses the typical problem of low-latency monitoring in two ways. First up, there's a pair of TRS jacks on the back for a stereo cue mix feed from your DAW.