The Focusrite Heritage Sound - in a versatile, transportable package

Back in the mid-1980s, Sir George Martin commissioned console design legend Rupert Neve to build a series of new, ‘no compromise’ console modules for AIR studios. They were an enormous hit and formed the basis of the Focusrite Studio Console, widely regarded as the best-sounding analogue recording console of all time. Today, the descendants of those modules are used in leading studios around the world, and their sought-after Focusrite Heritage Sound lies behind thousands of hit records. Today’s ISA Range from Focusrite puts the classic sound of Focusrite into your own studio or live performance.

Featuring a rugged, portable all-metal enclosure, the ISA One combines the classic Focusrite microphone preamp with a flexible, independent DI channel and optional 192kHz precision A/D conversion.

Read more about the Focusrite Heritage Sound

Classic Focusrite transformer-based mic preamplifier

At the heart of the ISA range is the microphone preamplifier with its Lundahl input transformer – essentially the same circuit, based on the original ISA110, that has been used for 30 years in successive Focusrite designs. The input transformer imparts a special character to the sound that can’t be truly emulated in any other way: inseparable from the microphone itself, the transformer input stage is ideal for use with classic microphones. But this mic pre has a twist the original didn’t have, which makes it far more versatile: four carefully-selected impedances allow you to match microphone to input in different ways. Bring out the character of a classic mic or emphasise a special feature, or go for a totally transparent, modern sound – it’s up to you.

Independent direct input

Whether you’re an artist, engineer or producer, you’ll appreciate the versatility of the ISA One, with its front-panel DI input. The DI includes low/high impedance switching and an amplifier output, and its own feed to the optional A/D converter and separate rear-panel XLR output


Key Features

ISA series transformer-based preamplifier

Encased in a rugged and portable chassis, ISA One offers the classic Focusrite microphone preamplifier at its lowest cost to date.

Flexible independent DI channel

ISA One is ideal for both engineers and demanding performers alike, featuring independent gain control, an output for routing to an amp, an independent XLR output on the rear and routing to the optional A-D converter.

Switchable impedance

Choose one of four carefully selected input impedances, including the original ISA110 setting, to suit any microphone.

Headphone output with volume control

ISA One can feed either a sum of the two input to the headphones output, or an external stereo cue mix (such as a stereo feed from an interface) via two TRS jack inputs on the rear of the unit.

Dedicated insert point

Allows you to place extra processing between the preamplifier or DI and the optional converter, such as an EQ or compressor.

Optional stereo 192kHz A-D converter

You can chose to upgrade your unit with an optional digital card that delivers the best A-D performance in its class (dynamic range of 118dB). Alternatively, the ISA One Digital comes with the A-D converter as standard.

Lundahl LL1538 Input Transformer

The original mic transformer used in the original Red modules helps to provide the unique sound and performance of this groundbreaking design.

Backlit VU meter with variable calibration

ISA One has a moving coil VU meter with variable calibration to suit analogue and digital recording media, alongside two six-LED peak meters; inputs can be metered either pre- or post-insert.


Analogue Channel Inputs

  • XLR Mic input
  • One XLR and one TRS line input
  • XLR Instrument input TRS Jack
  • External ADC input TRS Jack
  • TRS jack return

Analogue Channel Outputs

  • TRS jack send
  • XLR balanced line output
  • XLR DI output
  • TS jack DI through

Analogue Channel Additional I/O

  • TRS Jack cue mix left input
  • TRS Jack cue mix right input
  • 1/4” TRS Jack headphones output

Mic Input Response

Gain range 0dB to 60dB in 10dB steps + 20 dB of variable gain
Input Impedance Switched Impedance setting Equivalent Input Impedance at 1kHz Low = 600 Ohms
ISA110 = 1400 Ohms
Med = 2400 Ohms
High = 6800 Ohms
EIN (Equivalent Input Noise) -126dB measured at 60dB of gain with 150 Ohm terminating impedance and 22Hz/22kHz band-pass filter
Noise Noise at output with unity gain (0 dB) and 22 Hz-22 kHz band pass filter -97 dBu
Signal-to-Noise Ratio 106 dB relative to max headroom (9dBu)
Total Harmonic Distortion + Noise Measured at medium gain (30dB) with a 1kHz -20dBu input signal and with a 22Hz/22kHz band-pass filter < 0.0009%
Frequency Response At minimum gain (0 dB) -0.5dB down at 10Hz and -3dB down at 125kHz
  At maximum gain (60dB) -3dB down at 16Hz and -3dB down 118kHz
CMRR (Common Mode Rejection Ratio) 98dB (Channel 1, 1kHz, maximum gain with +24 dBu input)
Crosstalk Channel to Channel With 10dB@1kHz input to chA, chB output =104dBrA. With 10dB@10kHz input to chA, chB output = 84dBrA

Line Input Response

Gain range -20dB to +10dB in 10dB steps + 20 dB of variable gain
Input Impedance 10 kΩ from 10 Hz to 200 kHz
Noise Noise at main output with gain at unity (0 dB) measured with 50 Ω source impedance and a 22Hz - 22 kHz band pass filter -96 dBu
Signal-to-Noise Ratio Measured with a 22 Hz-22 kHz band pass filter 120 dB relative to max headroom (24 dBu)
118dB relative to 0dBFS (+22dBu)
Total Harmonic Distortion + Noise Measured with a 0 dBu input signal, and a 22 Hz-22 kHz band pass filter 0.0001%
Frequency Response At unity gain (0 dB) -0.3dB down at 10Hz and -3dB down at 200kHz

Instrument Input Response

Gain range 10dB to 40dB continuously variable
Input Impedance High = greater than 1M
Low =greater than 300k
Noise Measured with 22 Hz-22 kHz band pass filter Minimum gain (+10 dB): -92 dBu
Maximum gain (+40dB): -62dBu
THD At minimum gain (+10)
Frequency Response At minimum gain (+10 dB) -10dB input: 10Hz-100kHz +/- 0.6dB
  At maximum gain (+40 dB) -40dB input: -2.5dB down at 10Hz and 0dB at 100kHz


Moving Coil (MC) Meter factory calibrated to 0VU = +4dBu with 1kHz sinewave. With the VU Cal button pressed the meter can be adjusted on the rear panel to allow 0VU to equal +10dBu to +26dBu with the centre detent being equal to +22dBu.
Peak LED Meters Calibrated in the detent position for 0dBFS = +22dBu, calibration is adjustable on the rear panel to allow 0dBFS to equal +10dBu to +26dBu
Routing for MC and Peak1 meter is after the HPF, pre insert send or switched post insert return. Peak2 is always pre ADC channel 2, which can be fed by external input or Instrument input.
LED Levels As follows, when peak calibration is set to center detent on the rear panel. (This is when using the internal ADC). 0 = +22dBu
-2 = +20dBu
-6 = +16dBu
-12 = +10dBu
-18 = +4dBu
-42 = -20dBu
Frequency Response At minimum gain (+10 dB) -10dB input: 10Hz-100kHz +/- 0.6dB
  At maximum gain (+40 dB) -40dB input: -2.5dB down at 10Hz and 0dB at 100kHz

High-Pass Filter

Roll-Off 18 dB per octave (3 pole filter)
Frequency Fixed 75Hz measured at the 3dB down point

Weight and Dimensions

W x D x H 220mm (W) x 104mm (H) x 254 - 290mm (D - top to bottom) 8.66" (W) x 4.1" (H) x 10" - 11.4" (D - top to bottom)
Weight 3.9 kg 8.6 lbs