Focusrite ISA 428 MkII – 4-Channel Classic Mic Preamp with Variable Impedance and Optional A-D Conversion
The Focusrite ISA 428 MkII delivers four legendary Focusrite mic preamps in a powerful, flexible 2U rackmount unit. Built around the same transformer-based circuit as the original ISA 110, and featuring Lundahl LL1538 transformers on each input, the ISA 428 MkII offers pristine audio performance with wide bandwidth, low noise, and up to 80dB of total gain. With switchable input impedance—including the classic ISA 110 setting—you can fine-tune the mic match for any source.
The front panel provides easy access to instrument inputs on channels 1–4, while each channel includes a dedicated line input, a switchable insert point, and a variable high-pass filter (16Hz–420Hz) for maximum control. Visual feedback is handled by per-channel LED peak meters, including overload indicators.
For modern workflows, the ISA 428 MkII is fully RedNet Control compatible, and can be expanded with the optional ISA ADN8 A-D converter (sold separately), adding eight channels of 24-bit/192kHz digital output via Dante, ADAT, AES3, or S/PDIF.
Whether you're tracking vocals, drums, guitars, or line-level sources, the ISA 428 MkII provides the classic Focusrite sound that defined the golden era of British recording consoles—plus modern flexibility and rugged performance backed by a 3-year warranty.
At-a-Glance Highlights
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4 classic ISA transformer-based mic preamps with Lundahl LL1538 input transformers
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Variable input impedance with ISA 110 emulation
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Instrument inputs on front panel with dedicated controls
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High-pass filter (16Hz–420Hz) and switchable insert points per channel
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Optional ISA ADN8 card for Dante, ADAT, AES3 & S/PDIF digital output
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RedNet Control compatible for system integration
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Per-channel LED peak meters with overload indicators
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3-year warranty
Mic Inputs
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Frequency Response:
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At Min Gain: -0.35dB @ 20Hz, -3dB @ 122kHz
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At Max Gain: -2.5dB @ 20Hz, -3dB @ 103kHz
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Gain Range:
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0dB to +60dB (in 10dB steps)
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Plus 0dB to +20dB continuously variable trim
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Max Headroom: 7.4dBu
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EIN (Equivalent Input Noise): -126dB
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(Measured at 60dB gain, 150Ω termination, 20Hz–22kHz bandpass)
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Noise (Main Output, Unity Gain): -98dBu (20Hz–22kHz bandpass)
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SNR:
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123dB (relative to max output, 25dBu)
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120dB (relative to 0dBFS, 22dBu)
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CMRR: 88dB
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Input Impedance (Variable): 600Ω / 1400Ω / 2400Ω / 6800Ω
Line Inputs
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Frequency Response (Unity Gain):
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-0.3dB @ 20Hz
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-3dB @ 94kHz
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Gain Range:
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-20dB to +10dB (in 10dB steps)
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Plus 0dB to +20dB continuously variable trim
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Max Headroom: 25.4dBu
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THD+N: 0.002
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(Measured with 4dBu input, 0dB gain, 20Hz–22kHz bandpass)
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Noise (Main Output, Unity Gain): -91dBu (20Hz–22kHz bandpass)
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SNR:
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116dB (relative to max output, 25dBu)
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113dB (relative to 0dBFS, 22dBu)
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Input Impedance: 10kΩ
Instrument Inputs
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Gain Range: 10dB to 40dB (continuously variable)
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Max Headroom: 11.5dBu
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Noise (Main Output, Min Gain): -95dBu (20Hz–22kHz bandpass)
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Input Impedance: >1MΩ
High-Pass Filter
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Roll-Off: 18dB/octave (3-pole filter)
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Frequency Range: 16Hz to 420Hz (continuously variable, 3dB down point)
Analog Outputs
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Line Outputs:
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Insert Sends:
Other I/O
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Power Input: IEC Connector (100–240Vac, auto-switching)
