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Focusrite ISA One Single Channel Pre-Amp/DI

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Quick Overview

The Focusrite ISA One is a pre-amp and direct injection unit that features a VU meter, optional 192kHz A-D converter and a Lundahl LL1538 Input Transformer.

Focusrite ISA One Front


Back in the 1980’s Sir George Martin commissioned console legend Rupert Neve to create a series of new ‘no-compromise’ console modules for AIR Studios. The modules were a huge hit and formed the start of the Focusrite Studio Console, which is widely regarded as the best-sounding analogue recording console of all time. These days, the descendants of those modules are used in leading studios around the world, the sought-after Focusrite Heritage Sound is responsible for thousands of hit records. Today’s ISA Range from Focusrite puts that classic sound into your studio or live performance.

Focusrite ISA One

Sitting at the heart of the ISA One is a microphone preamplifier with a Lundahl input transformer, essentially the same circuit that is featured on the original ISA110 and has been used in Focusrite designs for over 30 years. The input transformer brings character to the sound that cannot be replicated or emulated in any other way and is perfect for use with classic microphones. However this mic pre-amp comes with a twist that allows it to become more versatile; four carefully-selected impedances let you input the microphone in different ways; give some character to classic mics, emphasise a unique feature or go with a completely transparent modern sound, it’s up to you.

The ISA One is housed in a portable, rugged all-metal enclosure and combines the original Focusrite microphone preamp alongside a flexible, independent DI channel and optional 192kHz precision A/D conversion. Whether you’re an artist, producer or engineer, you will love the versatility of the ISA One, especially the front-panel DI input with low to high impedance switching, amplifier output as well as its feed to the optional A/D converter and separate rear-panel XLR output.

  • ISA series transformer-based preamplifier
  • Flexible independent DI channel
  • Switchable impedance
  • Headphone output with volume control
  • Dedicated insert point
  • Optional stereo 192kHz A-D converter
  • Lundahl LL1538 Input Transformer
  • Backlit VU meter with variable calibration

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

Microphone Input Response

  • Gain Range: 0dB to 60dB in 10dB steps +20dB of variable gain
  • Input Impedance @1kHz: 1400Ohms
  • Equivalent Input Noise: -126dB measured at 60dB of gain with 150 Ohm terminating impedance and 22Hz/22kHz band-pass filter
  • Noise @0dB: -97dBu
  • Signal-to-Noise Ratio: 106dBu relative to max headroom (9dBu)
  • Total Harmonic Distortion + Noise: <0.0009%
  • Frequency Response @minimum gain (0dB): -0.5dB down at 10Hz and -3dB down at 125kHz
  • Frequency Response @maximum gain (60dB): -3dB down at 16Hz and -3dB down at 118kHz
  • Common Mode Rejection Ratio: 98dB (Channel 1, 1kHz, Maximum gain with +24dBu input)
  • Crosstalk Channel to Channel: With 10dB@1kHz input to chA, chB output=10dBrA. 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: 10kHz from 10Hz to 200kHz
  • Noise @0dB: -96dBu
  • Signal-to-Noise Ratio: 120dB relative to max headroom (24 dBu). 118dBu relative to 0dBFS (+22dBu)
  • Total Harmonic Distortion + Noise: 0.0001%
  • Frequency Response: -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 (minimum gain +10dB): -92dBu
  • Noise (maximum gain +40dB): -62dBu
  • Frequency Response @minimum gain (+10dB): -10dB: 10Hz-100kHz +/-0.6dB
  • Frequency Response @maximum gain (+40dB): -2.5dB down at 10Hz and 0dB at 100kHz


  • Moving Coil 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 (when using the internal ADC).0= +22dBu, -2= +20dBu, -6= +16dBu, -12= +10dBu, -18= +4dBu, -42= -20dBu
  • Frequency Response @-10dB input: 1-Hz-100kHz +/- 0.6dB
  • Frequency Response @-40dB input: -2.5 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

  • WxDxH: 220mm W x 254 - 290mm D x 104mm H
  • Weight: 3.9Kg.

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Focusrite ISA One Single Channel Pre-Amp/DI