ISA 428 MkII

Description

The ISA Two by Focusrite brings together a fully independent pair of legendary ISA microphone preamps from the original ISA 110 module, blending the best of traditional solid-state electronics with the original input transformer specified by Rupert Neve: the Lundahl LL1538. Two is the perfect number for recording, whether it’s vocals and an instrument or a stereo piano. Even if you only need two mic preamps, you owe it to your craft to choose the best. (And if you need more, Focusrite also offers the 4-channel ISA 428 Mk II and the 8-channel ISA 828.)

We've made a small tweak to the mic preamp. The original ISA 110 had a single input impedance, ideal for the microphones of its era. We've added three more, allowing you to get the best sound from any microphone, old or new. Give a vintage mic the input it expects for a classic warm sound. Pair ISA Two with modern mics for the most transparent sound possible. Or experiment and bring out unique characteristics in any microphone you choose. With up to 80 dB of gain, you’re ready for anything.

Beyond the mic preamps, instrument inputs are conveniently located on the front panel, with line inputs on the rear. A balanced insert point on the back panel allows easy integration of EQs, dynamics, or other processors, all controllable with a front-panel switch. User-calibrated 8-LED metering and a variable high-pass filter complete the package, ensuring the ISA Two provides everything needed for the highest-quality recordings.

Key Features

• Lundahl LL1538 Microphone Input Transformer – Originally chosen by Rupert Neve for the ISA 110, the Lundahl LL1538 remains the best available microphone input transformer and is used across the ISA series. The precisely tuned Zobel network enhances the circuit’s performance for pristine sound.
• Up to 80 dB of Gain – ISA Two delivers up to 80 dB of clean, distortion-free gain, with low noise even at high gain settings. The transformer alone provides 20 dB of gain, while the ISA input stage adds up to 60 dB, reaching an impressive 80 dB maximum gain.
• Variable Input Impedance – Four input impedance options, including the original ISA 110 setting, let you tailor the preamp to any microphone, ensuring the best possible sound. Impedance is selectable via a front-panel switch and remains stored even when powered off.
• User-Calibrated Metering – Each channel features an 8-LED metering array for clear level indication. A rear-panel calibration button lets you align analog levels with your DAW converters, ensuring proper gain staging and avoiding clipping.
• Front Panel Instrument and Rear Panel Line Inputs – Two 1/4-inch jack inputs on the front provide instant access to a clean DI input. Rear-panel TRS line inputs are also available, selectable at the push of a button.
• Variable High-Pass Filter – Featuring a smooth 18 dB/octave slope, the same design as the original ISA 110 module, the high-pass filter allows precise control over low-end rumble and unwanted noise, adjustable from 16 to 420 Hz.
• Balanced Insert Points – Each ISA Two channel includes a balanced insert point with 1/4-inch TRS send and return connections. Easily integrate external processing and engage/disengage with the illuminated front-panel switch.

Detailed Specifications

Microphone Input Response

• Gain Range (Microphone): 0 dB to 60 dB in 10 dB steps, plus continuous variable trim from 0 dB to 20 dB
• EIN (Microphone): Measured at 60 dB gain with 150Ω source impedance and 22 Hz-22 kHz bandpass filter: -127 dB
• Noise (Microphone): Output noise with unity gain (0 dB) and 22 Hz-22 kHz bandpass filter: -97 dBu
• Frequency Response (Microphone):
  At minimum gain (0 dB): -0.5 dB at 10 Hz, -1 dB at 135 kHz (relative to 1 kHz)
  At 60 dB gain: -6 dB at 10 Hz, -1 dB at 115 kHz (relative to 1 kHz)
• Channel-to-Channel Crosstalk (Microphone): Mic input with I/P = 0 dBu, gain = 0 dB @ 1 kHz input to Channel A, output from Channel B = -85 dB

Line Input Response

• Gain Range (Line): -20 dB to 10 dB in 10 dB steps, plus continuous variable adjustment from 0 dB to 20 dB
• Input Impedance (Line): 10 kΩ from 10 Hz to 200 kHz
• Frequency Response (Line): At minimum gain (0 dB): -0.3 dB at 10 Hz, -1 dB at 80 kHz (relative to 1 kHz)
• Channel-to-Channel Crosstalk (Line): Line input with I/P = 0 dBu, gain = 0 dB @ 1 kHz input to Channel A, output from Channel B = -91 dB

Instrument Input Response

• Gain Range (Instrument): Continuous variable trim from 10 dB to 40 dB
• Input Impedance (Instrument): 2 MΩ
• Noise (Instrument):
  Measured with 22 Hz-22 kHz bandpass filter
  Minimum gain (10 dB): -95 dBu
• Frequency Response (Instrument):
  At minimum gain (10 dB): -0.1 dB at 10 Hz, -1 dB at 115 kHz (relative to 1 kHz)
  At maximum gain (40 dB): -2.5 dB at 10 Hz, -1 dB at 110 kHz (relative to 1 kHz)

High-Pass Filter

• Roll-Off: 18 dB per octave (3-pole filter)
• Frequency Range: Continuously variable from 16 Hz to 420 Hz (-3 dB)