Dual-mono mic preamp

Back in 1985, George Martin commissioned Rupert Neve to create a channel strip—and its ISA 110 mic preamp became the genesis of the ISA Series. The ISA Two continues that tradition with a dual-mono preamp that’s intended to provide a quality link between your mics/ instruments and recorder.

The Signal Path Audio enters via rear-panel XLR mic or 1/4" TRS line ins. (Both preamps have identical I/O.) Front-panel 1/4" jacks with a 2-Megohm input impedance provide a convenient DI for instruments. Lundahl LL1538 input transformers, which are wound to extend high-frequency response (mic/DI ins are down less than –1dB at 100kHz @ 60dB gain), not only add that bit of inductive “warmth” but also provide 20dB of gain to help boost the signal-to-noise ratio.

The XLR outs are complemented by 1/4" TRS insert send and receive jacks. Signal always feeds the send jack, thus providing a parallel preamp out, while a front-panel insert in/ out switch routes the return to the output. A standard IEC cable feeds the internal “global” power supply (100–240V, 50/60Hz); the unit comes with a variety of plugs for different AC power sources.

Controls The two channels have identical controls. One button steps through the three inputs, while another steps through four different mic input impedances. Switchable impedance can change a mic’s character, so this isn’t just about matching. Regarding gain, a “master” gain range button selects either a 0–30dB or 30–60dB range. A Gain control has four steps that each represent 10dB of change (e.g., –20, –10, 0, or +10dB for the line in and 0–30, 10–40, 20–50, or 30–60dB for the mic in). An additional trim control can add up to 20dB of additional gain for the mic and line ins, or serve as an input level control for the instrument input.

Buttons for phase (polarity) flip and +48V phantom power, along with a three-pole highpass filter (16–420Hz, 18dB/octave slope) and accompanying in/out button, round out the controls. Metering is two 8-stage LED meters that can be custom calibrated using two rearpanel trim controls.

In Use Don’t underestimate the value of selectable impedance. Lower impedances tend to emphasize lows, while higher impedances give a brighter sound and a touch more level. This is particularly obvious with dynamic mics, and adds a couple “free mics” to your mic locker. The sound is “open,” with that slight warmth from using transformers, and the noise level seemed lower than expected—again, the transformers help here, due to the extra gain. Crosstalk and common-mode rejection specs are also excellent.

Overall, this is an “obvious” preamp. It’s easy to use, has all of the expected I/O and controls (and then some), and you can set up your sound in minutes—the lit buttons help you parse settings that much faster. Having one switch and two controls for setting gain may seem excessive, but that configuration makes it easy to dial in the right amount of gain, as well as repeat settings.

Note that the ISA Two doesn’t replace the ISA One; instead, it extends the line into a convenient, 1U format for dual-mono preamplification. As more project studios recognize the importance of mic preamps in the signal chain, the ISA Two delivers no-nonsense preamplification at a reasonable price.

SUMMARY

STRENGTHS: Selectable input impedance. Quality input transformers add character and improve the signal-to-noise ratio. Open-sounding preamps. DI for instruments. 80dB gain is enough for ribbon mics.

LIMITATIONS: Nothing significant.

$1,099.99 MSRP focusrite.com