Focusrite ISA428 MkII - Microphone Preamp

Focusrite ISA428 MkII - Microphone Preamp

Focusrite ISA428 MkII - Microphone Preamp

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Expected availability: 7-14 business days

Product Highlights

  • 4 Channels
  • Transformer Based
  • Selectable Impedance
  • Phantom Power
  • Instrument Inputs
  • Variable High-Pass Filter
  • Per Channel LED Metering
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Focusrite ISA428 MkII overview

  • 1Description

The ISA428 MkII from Focusrite is a four-channel microphone preamp featuring Focusrite's transformer-based preamps. With selectable input impedance, direct instrument inputs and an optional eight channels of high-quality analog to digital conversion, the unit is a perfect front end for the audio professional, whether utilizing digital or analog recording.

The ISA microphone preamp holds a reputation for delivering transparency along with subtle warmth derived from transformer core saturation. The addition of a variable impedance circuit allows users to perfectly match the preamp with any microphone, or to use different settings creatively to shape the sound of the microphone.

The extremely broad frequency response of Focusrite preamps (close to 200kHz at the top end) guarantees accurate phase response across the range of human hearing, with the roll-off point being moved entirely outside of the audible hearing range. Warmth, plus beautifully open, unrestricted high frequencies, is a classic hallmark of the mid 80's Focusrite designs to which this preamp owes its design.

The optional eight channel analog converter utilizes high-quality Burr-Brown amplifiers and PCM4220 A-D converter chips seated within Focusrite's custom analog circuitry. Specifications include a dynamic range of 122dB and jitter performance below 250 picoseconds. The card can be retrofitted at any time and due to the convenient 25-pin D-type connector, it integrates seamlessly with most digital workstations, including Pro Tools.

Four ISA Series Transformer-Based Preamps
ISA series microphone preamps have been the producers' choice on countless hit records over the last two decades
Eight-Channel Optional A-D Converter
Four additional A-D converter inputs allow eight channels of high-quality conversion, with a dynamic range of 122dB and jitter performance below 250 picoseconds
Selectable Impedance
Ideal for microphone matching or extended microphone creativity - settings include the "Vintage ISA110" setting that provides the original Focusrite signature sound

Four Front Panel Instrument Inputs

Instant access on the front fascia - no separate DI box required
Dedicated Analog Insert Points
Switchable insert points are featured on every channel, allowing routing (between pre-amp and output) through additional external processing
Variable High-Pass Focusrite Filter
Provided on every channel, this is the same filter as featured on the original ISA428
Accurate LED Meters for Every Channel

Clear metering designed to catch even the fastest and most elusive of transients
Additional Features
  • Phantom power available on every channel
  • Trim control allows 20dB of extra gain with fine adjustment
  • Phase reverse buttons help to correct phase issues with microphones or cables
  • Optional A-D converters easily synchronize to external Wordclock
UPC: 815301005124
In the Box
Focusrite ISA428 MkII - Microphone Preamp
  • AC Power Cable
  • Limited 2-Year Warranty
  • Table of Contents
    • 1Description

    Focusrite ISA428 MkII specs

    Number of Channels 4
    Inputs 4 x XLR Microphone (rear panel)
    4 x 1/4" TS phone Instrument (front panel)
    4 x 1/4" TRS phone Line (rear panel)
    4 x 1/4" TRS phone Insert Return (front Panel)
    4 x XLR ADC Input for optional AD converter card (rear panel)
    Output 4 x XLR Line (rear panel)
    4 x 1/4" TRS phone Insert Send (rear panel)
    Phantom Power +48V individually switchable
    Multi Function Has provision for optional analog to digital converter
    Gain Range Microphone: 0dB to +60dB in 10dB steps, plus 0dB to +20dB continuously variable trim
    Line: -20dB to +10dB in 10dB steps, plus 0dB to +20dB continuously variable trim
    Instrument: +10dB to +40dB continuously variable
    Input Impedance Microphone: 600Ω, 1.4kΩ, 2.4kΩ, 6.8kΩ
    Line: 10kΩ
    Instrument: >1MΩ
    Maximum Output Level Microphone: +7.4dBu
    Line: +25.4dBu
    Instrument: +11.5dBu
    Frequency Response Microphone: -0.35dB at 20Hz and -3.0dB at 122kHz (0dB gain) and -2.5dB at 20Hz and -3.0dB at 103kHz (60dB gain)
    Line: -0.3dB at 20Hz and -3dB at 94kHz (0dB gain)
    Instrument: -0.2dB at 20Hz and 0dB at 200kHz (+10dB gain) and -3.0dB at 20Hz and -3.0dB at 38.4kHz (+40dB gain)
    THD + N Microphone: 0.0009% (measured at 1kHz, -20dBu input signal, at 30dB gain setting, with a 20Hz/22kHz bandpass filter)
    Line: 0.002% (measured with +4dBu input signal, 0dB gain setting, with a 20Hz/22kHz bandpass filter)
    Instrument: 0.006% (measured with -20dBu input signal, at minimum gain (+10dB), with a 20Hz/22kHz bandpass filter)
    Noise Microphone:

    • Noise EIN: -126dB (measured at 60dB of gain with 150Ω termination and 20Hz/22kHz bandpass filter)
    • Noise at main output with unity gain: -98dBu (measured with a 20Hz/22kHz bandpass filter)
    • SNR: 123dB (relative to max output 25dBu)
    • SNR: 120dB (relative to 0dBFS (+22dBu)


    • Noise at main output with unity gain: -91dBu (measured with a 20Hz/22kHz bandpass filter)
    • SNR: 116dB (relative to max output 25dBu)
    • SNR: 113dB (relative to 0dBFS +22dBu)


    • Noise at main output with minimum gain (+10dB): -95dBu (measured with a 20Hz/22kHz bandpass filter)
    CMRR Microphone: 88dB
    Meters Each 6-LED meter is calibrated 0dBFS = +22dBu (the maximum level which can be correctly converted by the optional internal A/D converter before overload occurs). The meter calibration points are as follows:

    Meter panel calibration value in dBFS / Equivalent dBu value:

    • 0dBFS / +22dBu
    • -2dBFS / +20dBu
    • -6dBFS / +16dBu
    • -12dBFS / +10dBu
    • -18dBFS / +4dBu
    • -42dBFS / -20dBu
    Power Requirements 100VAC~240VAC
    Dimensions (WxDxH) 19 x 11 x 3.5" (483 x 279 x 89mm)
    Weight 12.2 lbs (5.5kg)
    Specialties High Pass Filter
    Roll off = 18dB per octave 3 pole filter
    Frequency range: 16Hz to 420Hz (continuously variable, measured at the 3.0dB down point)
    Packaging Info
    Package Weight 17.55 lb
    Box Dimensions (LxWxH) 25.0 x 18.0 x 9.0"

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