Focusrite ISA 428 MkII 4-Channel Rack-Mount Transformer-Based Microphone Preamplifier

The Focusrite ISA 428 MkII houses four acclaimed transformer-based ISA mic preamps in a compact 2U rack enclosure. With selectable input impedance, front-panel instrument inputs, insert points, LED metering, and optional onboard A-D conversion, it offers both classic sonic character and modern flexibility.

Each channel delivers up to 60 dB of stepped gain plus an additional 20 dB trim (80 dB total), a variable high-pass filter (16–420 Hz), and transformer-driven warmth. Add the optional A-D conversion card to integrate eight analog inputs with high-quality digital output.

Key Features

• Mic Preamps: 4 transformer-based ISA series mic pres with Lundahl LL1538 transformers
• Gain Range: 0–60 dB stepped, plus 0–20 dB continuous trim (80 dB max)
• Input Types: Mic (XLR), Line (TRS), front-panel Instrument (¼″ TS)
• Input Impedance: Selectable: Low (600 Ω), ISA 110 (∼400 Ω), Medium (2.4 kΩ), High (6.8 kΩ)
• High-Pass Filter: 18 dB/octave, 16–420 Hz (continuously variable)
• Inserts: Switchable per channel for outboard processing
• Metering: 6-segment LED peak meters per channel
• Optional A-D Conversion: Internal 8-channel AD card (ADAT/AES3, up to 192 kHz, 122 dB dynamic range)
• Connectivity & Power: IEC mains (100–240 V), rear-panel I/O including mic/line inputs, inserts, outputs; sealed 2U rack unit requiring 75 mm rear clearance
• Warranty: 3-year manufacturer warranty (as with other ISA products)

Technical Specifications

• Dimensions: 19" W × 3.5" H × 11" D (480 × 88 × 280 mm)
• Weight: 12.2 lb (5.5 kg)
• Package Weight: 15.5 lb (7.03 kg)
• Box Dimensions: 25" × 18" × 9"
• Gain (Mic): Up to 80 dB total
• HP Filter: 16–420 Hz, 18 dB/octave
• Impedance Settings: 600 Ω, 400 Ω, 2.4 kΩ, 6.8 kΩ
• Metering: 6-segment LED

What's Included

• 1x ISA 428 MkII unit
• 1x IEC power cable
• 1x User manual
• 3-year warranty
• Optional: A-D conversion card (sold separately)