Focusrite ISA 428 MkII 4-Channel Transformer Mic Preamp

The Focusrite ISA 428 MkII is a four-channel transformer-based mic preamp in a 2U rackmount chassis, featuring four ISA preamp circuits with Lundahl LL1538 input transformers and a rear-panel expansion slot for the optional ISA ADN8 A-D converter card.

Preamp Controls

Each channel provides up to 80dB of gain (60dB in 10dB steps, plus 20dB of variable trim) with four-position input impedance switching (600Ω, 1.4kΩ ISA 110, 2.4kΩ, 6.8kΩ). A variable high-pass filter with continuously adjustable cutoff from 16Hz to 420Hz at 18dB/octave offers precise low-end control. Four front-panel 1/4" instrument inputs and rear-panel mic, line, and insert connections cover all recording scenarios.

Digital Expansion

With the optional ISA ADN8 card installed, the four preamp outputs plus four additional rear-panel XLR inputs feed eight channels of 24-bit/192kHz A-D conversion with Dante, AES3, and ADAT outputs. Six-segment LED meters per channel, plus metering for the four additional A-D card inputs, provide clear level monitoring.

Connectivity

• 4 x XLR mic inputs (rear panel)
• 4 x 1/4" TRS line inputs (rear panel)
• 4 x 1/4" TS instrument inputs (front panel)
• 4 x XLR balanced outputs
• 4 x 1/4" TRS insert send/return (rear panel)
• 4 x XLR A-D inputs (rear panel, active with optional ADN8 card)
• Optional ISA ADN8 digital card slot

Specifications

• Mic gain range: 0 to 60dB (10dB steps) + 20dB trim
• Mic input impedance: 600Ω, 1.4kΩ (ISA 110), 2.4kΩ, 6.8kΩ
• Mic EIN: -126dBu
• Variable high-pass filter: 16-420Hz, 18dB/octave
• Phantom power: +48V, switchable in groups
• Max output level: +24dBu
• Form factor: 2U rackmount
• Power: Internal PSU, 100-240V AC