Focusrite ISA428 MkII 4-Channel Microphone Preamplifier (B-Stock)

The Focusrite ISA428 MkII consolidates four channels of legendary, transformer-based console preamplification into a single 2U rackmount unit. Built around four historic Lundahl LL1538 input transformers, this powerhouse deliver up to $80\text{ dB}$ of clean, low-noise analog gain per channel. Perfect for tracking full drum setups, multi-mic acoustic instruments, or live ensembles.

Each channel features a four-position impedance selector switch allowing you to tailor how your microphone interacts with each Lundahl transformer.

To streamline modern tracking sessions, channels 1–4 feature dedicated front-panel instrument DIs, making it easy to plug in bass guitars, guitars, or synthesizers directly. For those looking to expand their digital connectivity, the ISA428 MkII supports an optional, premium 8 channel A-D converter card. This allows you to patch processing gear into the rear analog inserts and feed clean digital signals directly to your DAW, or use the converter's four extra line inputs to route auxiliary outboard preamps straight to your interface.

Key Features

• Quad Lundahl LL1538 Transformers: Classic, industry-standard input transformers that deliver the signature warm low end and airy top end of historic ISA consoles.
• Up to 80dB of Linear Gain: Delivers plenty of clean, transparent headroom to comfortably power low-output ribbon, dynamic, or condenser microphones.
• Front-Panel Instrument DIs: Four high-impedance ($2\text{ M}\Omega$) TS inputs allow you to track direct instruments effortlessly without external boxes.
• Variable High-Pass Filters: Fully adjustable from $16\text{ Hz}$ to $420\text{ Hz}$ with a steep $18\text{ dB}$/octave slope to eliminate unwanted rumble and low-end buildup.
• Dedicated Rear Analog Inserts: Balanced TRS loop sends and returns on every channel let you easily patch in external outboard compressors, limiters, or EQs.
• Clear 6-Segment LED Metering: High-resolution LED meters provide quick, precise visual feedback of input levels across all four channels.
• Optional 8-Channel A-D Card: Supports an optional high-performance conversion card (Dante, AES3, and ADAT) utilizing four additional line inputs for extra external gear.

Specifications

• Preamplifier Type: Solid State with Quad Lundahl LL1538 Input Transformers
• Channel Count: 4 Channels (Quad-mono tracking)
• Maximum Gain: Up to $80\text{ dB}$ (Mic) / Up to $28\text{ dB}$ (Instrument DI)
• Variable Impedance Settings: Low ($600\Omega$), ISA 110 ($1,400\Omega$), Medium ($2,400\Omega$), High ($6,800\Omega$)
• High-Pass Filter: Variable $16\text{ Hz – }420\text{ Hz}$ ($18\text{ dB}$ per octave slope)
• Analog Inputs (Rear): 4x XLR Microphone Inputs, 4x TRS Balanced Line Inputs
• Analog Inputs (Front): 4x TS Unbalanced Instrument DI Inputs
• Analog Outputs: 4x XLR Balanced Line Outputs
• Hardware Inserts: 4x TRS Sends, 4x TRS Returns (1/4" balanced, switchable per channel)
• Optional Conversion Expansion: Focusrite ISA 8-Channel A-D Card (Adds 4x DB-25 line-level return inputs)
• Chassis Format: 2U Standard 19" Rackmount