Focusrite ISA One Classic Microphone Preamp with Independent DI

Overview

The Focusrite ISA One is a professional transformer-based microphone preamp designed for recording microphones, line-level sources, and instruments with exceptional clarity, character, and control. Built around the renowned Lundahl LL1538 input transformer and inspired by the original ISA 110 circuit, ISA One delivers the distinctive Focusrite sound in a rugged, portable desktop format.

Alongside its high-quality microphone preamp, ISA One features an independent front-panel DI channel with selectable impedance, dedicated gain control, amplifier output, and separate XLR output. With flexible routing, analogue insert connectivity, headphone monitoring, precision metering, and an optional digital expansion card, ISA One is equally suited to professional studios, mobile recording setups, tracking sessions, and live performance applications.

Key Features

• Transformer-based Focusrite ISA microphone preamp with Lundahl LL1538 input transformer
• High-quality microphone, line-level, and instrument input support
• Four selectable microphone input impedance settings for flexible microphone matching
• Independent front-panel DI input with selectable high and low impedance
• Dedicated DI amplifier output and rear-panel XLR DI output
• Dedicated insert send and return for external EQ, compression, or other processing
• Switchable 75 Hz high-pass filter, phantom power, and polarity control
• Variable-gain controls for precise signal adjustment
• Headphone output with independent level control and stereo cue monitoring
• Moving-coil VU meter plus LED peak metering
• Optional ISA ADN2 digital expansion card with Dante, AES3, ADAT, and S/PDIF connectivity
• Rugged, portable all-metal enclosure with integrated carrying handle

Classic ISA Transformer Preamplification

At the heart of ISA One is Focusrite's transformer-based microphone preamp, based on the original ISA 110 design. The Lundahl input transformer provides a distinctive character while maintaining the detail and accuracy expected from a professional recording preamp. With up to 60 dB of stepped gain plus 20 dB of variable trim, ISA One provides precise control for a wide range of microphones and recording sources.

Flexible Microphone Impedance

ISA One provides four selectable microphone input impedance settings: Low, ISA 110, Medium, and High. This allows engineers to tailor the interaction between the preamp and microphone, helping to shape the tonal response and make the most of different microphone designs.

Independent DI for Guitar and Bass

The dedicated front-panel DI input makes ISA One particularly useful for recording electric guitar, bass, and other instruments directly. High and Low impedance settings allow the input to accommodate different instruments and pickups, while an independent gain control provides precise level adjustment.

A parallel amplifier output allows the instrument signal to be routed to a guitar or bass amplifier, while the separate rear-panel XLR DI output provides a convenient direct signal for connection to a recording system or mixing console.

Insert Processing and Signal Control

A dedicated balanced insert send and return lets you integrate external processors directly into the signal path. This is useful for adding an EQ, compressor, or other analogue processor before sending the signal to the main output or optional digital conversion stage.

ISA One also provides +48V phantom power, polarity reversal, and a switchable 75 Hz high-pass filter, giving engineers practical control over microphone and line-level signals during recording.

Headphone and Cue Monitoring

The built-in headphone output provides convenient monitoring directly from ISA One, with its own volume control. Headphones can monitor the selected input signal or an external stereo cue mix connected through the rear-panel Cue Mix inputs, making the unit useful for performers during tracking sessions.

Professional Metering

ISA One combines a traditional moving-coil VU meter with LED peak metering for clear signal monitoring. Meter calibration can be adjusted to suit different analogue and digital recording environments, while the metering point can be switched to monitor the signal before or after the insert.

Optional Digital Expansion

For digital recording and networked studio systems, ISA One supports the optional ISA ADN2 A-D converter card. The expansion provides high-quality stereo digital conversion with Dante networking as well as AES3, ADAT, and S/PDIF connectivity, allowing ISA One to integrate directly into modern digital production environments.

Portable Professional Design

Designed for both studio and mobile use, ISA One features a rugged all-metal enclosure, rubber feet, and a top-mounted carrying handle. Its compact desktop format makes it easy to position beside an audio interface, mixing console, or recording workstation, while the universal 100–240V internal power supply supports use with different mains voltages.

Typical Uses

• Professional vocal and microphone recording
• Electric guitar and bass DI recording
• Microphone preamplification for studio sessions
• External analogue processing through the insert loop
• Mobile recording and remote production setups
• Tracking through an audio interface or mixing console
• Live performance and instrument amplification workflows
• Digital studio integration with the optional ISA ADN2 card

Specifications

• Mic Gain Range: 0 to 30 dB or 30 to 60 dB in 10 dB steps, plus 0 to 20 dB variable trim
• Mic Input Impedance: 600 Ω, 1.4 kΩ, 2.4 kΩ, or 6.8 kΩ
• Maximum Mic Input Level: +7 dBu
• Line Gain Range: -20 to +10 dB in 10 dB steps, plus 0 to 20 dB variable trim
• Maximum Line Input Level: +25 dBu
• Instrument Gain Range: +10 to +40 dB continuously variable
• Instrument Input Impedance: 470 kΩ Low / 2.4 MΩ High
• High-Pass Filter: 75 Hz, 18 dB/octave
• Microphone S/N Ratio: 122 dB A-weighted typical
• Mic EIN: Less than -123 dBu
• Frequency Response: 20 Hz–20 kHz ±0.2 dB for microphone input
• Mic Input: XLR-3 female
• Line Input: Balanced 1/4-inch TRS and XLR
• Main Output: XLR-3 male
• DI Output: XLR-3 male
• Instrument Input: 1/4-inch mono jack
• Amp Output: 1/4-inch mono jack
• Insert: Balanced 1/4-inch send and return
• Cue Mix: Stereo balanced 1/4-inch inputs
• Digital Expansion: Optional ISA ADN2 card
• Power Supply: Internal universal 100–240V AC
• Power Consumption: 35W
• Dimensions: 220 × 104 × 290 mm
• Weight: 3.9 kg

What's Included

• Focusrite ISA One
• AC power lead
• Safety information cut sheet

Note: The optional ISA ADN2 digital conversion card is not included with the standard ISA One analogue model.

Why Choose the Focusrite ISA One?

The Focusrite ISA One combines classic transformer-based Focusrite preamplification with a highly flexible independent DI channel, professional metering, analogue insert connectivity, and convenient headphone monitoring. Its selectable microphone impedance and optional digital expansion make it a versatile choice for engineers, producers, musicians, and studios that need premium analogue front-end performance in a compact and portable design.