Focusrite ISA 428 MKII

Description

Focusrite ISA microphone preamplifiers date back to 1985, when Sir George Martin asked console designer Rupert Neve to create new modules for the AIR Studio console in Montserrat. The modules created included the legendary ISA110, on which all ISA microphone preamplifiers are based. With their characteristic Lundahl LL1538 input transformer, and a concession to modernity - variable input impedance - ISA microphone preamplifiers are very similar to what they were 30 years ago. But today, instead of exclusively gracing consoles at AIR Studio, ISA microphone pres are at the heart of hundreds of hits produced in the world's most important studios by the best engineers, artists, and producers.

Now in its second generation, the ISA 428 Mk II incorporates 4 renowned Focusrite microphone pres in an easy-to-use layout with a 2-rack unit footprint, giving you 4 microphone preamplifiers, instrument inputs, and line inputs at your fingertips. The original Focusrite microphone pre was designed for microphones of the time; today's model features a small change: with the addition of 3 additional input impedances to the classic ISA110 settings, it allows you to match any microphone and access a wide range of sounds, from the character and warmth of a vintage microphone to the clear transparency of modern microphones. Or you can experiment and highlight the qualities you desire. Front panel instrument inputs.

3-year warranty on all new Focusrite products purchased from January 1, 2018 onwards. The Focusrite Warranty means peace of mind for the user, representing a professional service that minimizes waiting times should a manufacturing defect occur, and confirms that the English company's products are built to high quality standards.

In addition to the microphone inputs, there are 4 instrument inputs on the front panel, making the ISA428 Mk II ideal for overdubs in the control room without needing a DI box. On the rear panel: 4 line inputs and switchable insert points on each channel allow routing through an external signal processor. An optional 8-channel precision A-D converter with 122 dB dynamic range and superb jitter performance is available for the ISA428 Mk II - ideal for simple interaction with your DAW.

Main features

4 ISA series preamplifiers with transformer

ISA series microphone preamplifiers have been the choice of producers on countless hit records over the past two decades.

Optional 8-channel A-D converter

Four additional A-D converter inputs allow for quality 8-channel conversion, with a dynamic range of 122dB and jitter below 250 picoseconds.

Selectable impedance

Ideal for matching microphones or expanding creativity. Settings include 'Vintage ISA110' which provides the original Focusrite sound.

4 instrument inputs on the front panel

Immediate access from the front panel - no separate DI boxes required.

Dedicated analog insert points

Switchable insert points on each channel allow routing (between preamp and output) through additional external processing.

Accurate LED meters for each channel

Clear metering designed to capture even the fastest and most elusive transient.

Main technical specifications:

Four ISA Series transformer-based preamplifiers
Optional 8-channel A-D converter
Selectable Impedance
Four front panel instrument inputs
Dedicated Analog Insert Points
Focusrite Variable High-Pass Filter
Highly accurate LED Meters on each channel

Other features:

Phantom power on each channel
A Trim control allowing 20dB of extra gain with precise adjustments
Phase inversion buttons that help correct phase problems with microphones and cables
Optional A-D converter that easily synchronizes to an external word clock

Mic Inputs

Frequency response at minimum gain (0dB): -0.35dB at 20Hz and –3dB at 122kHz
Frequency response at maximum gain (60dB): –2.5dB at 20Hz and –3dB at 103kHz
Gain range: 0dB to +60dB in 10dB steps, plus 0dB to +20dB with continuously variable trim
Maximum headroom: +7.4dBu
THD+N: 0.0009% (measured with a 1kHz -20dBu signal, at 30dB gain, with a 20Hz/22kHz bandpass filter)
EIN noise: -126dB (measured at 60dB gain with 150Ω termination and 20Hz/22kHz bandpass filter)
Main output noise at unity gain: -98dBu (measured with 20Hz/22kHz bandpass filter)
SNR: 123dB (relative to maximum output of 25dBu)
SNR: 120dB (relative to 0dBFS (+22dBu)
CMRR: 88dB. Input impedance, variable as follows:

Impedance setting Equivalent value at 1kHz

Low 600Ω
ISA110 1400Ω
Med (Medium) 2400Ω
High 6800Ω

Line Inputs

Frequency response at unity gain (0dB): -0.3dB at 20Hz and –3dB at 94kHz
Gain range: -20dB to +10dB in 10dB steps, plus 0dB to +20dB with continuously variable trim
Maximum headroom: +25.4dBu
THD+N: 0.002% (measured with a +4dBu signal, with gain set to 0dB, and 20Hz/22kHz bandpass filter)
Noise on main output at: -91dBu (measured with 20Hz/22kHz bandpass filter)
SNR: 116dB (relative to maximum output of 25dBu)
SNR: 113dB (relative to 0dBFS +22dBu). Input impedance: 10kΩ

Instrument Inputs

Frequency response at +10dB gain: -0.2dB at 20Hz and 0dB at 200kHz
Frequency response at +40dB gain: -3dB at 20Hz and –3dB at 38.4kHz
Gain range: +10dB to +40dB continuously variable
Maximum headroom: +11.5dBu
THD+N: 0.006% (measured with an input signal of –20dBu, at minimum gain (+10dB), with 20Hz/22kHz bandpass filter)
Noise on main output at minimum gain (+10dB): -95dBu (measured with a 20Hz/22kHz bandpass filter)
Input impedance = >1MΩ

High-Pass Filter

Roll off = 18dB per octave, 3-pole filter
Frequency range: 16Hz to 420Hz (continuously variable, measured at -3dB)

Meters

6-LED meter, calibrated as follows: 0dBFS = +22dBu (Maximum level that can be correctly converted by the optional internal AD converter before overload occurs)

The meter calibration points are:

Analog Channel Inputs (Inputs 1-4)

4 instrument inputs on front panel 1/4” TS jacks
4 microphone inputs on rear panel XLR
4 line inputs on rear panel 1/4” TRS jacks
4 insert returns on rear panel 1/4” TRS jacks
4 ADC inputs on rear panel XLR

Analog Audio Outputs (Outputs 1-4)

4 line outputs on rear panel XLR
4 insert sends on rear panel 1/4” TRS jack

Other I/O

IEC 100Vac – 240Vac power input connector

Front panel indicators

8 x 6-segment output meters
4 x 30-60 mic gain range selection indicators
4 x +48V phantom power indicators
4 x Phase indicators
4 x Insert In indicators
4 x Filter In indicators
4 x Input selection indicators (Mic, Line, Inst)
4 x Z In input impedance selection indicators (Low, ISA110, Med, High)
Clock selection indicators (44.1, 48, 88.2, 96, 176.4, 192)
Ext clock indicators (Lock, Word clock, 256X)

Dimensions (W x H x D)

Unboxed: approx. 480 mm x 88 mm x 280 mm (19 x 3.5 x 11 inches)
Boxed: approx. 620 mm x 460 mm x 210 mm (24.4 x 18.1 x 8.3 inches)

Weight

Net: 5.5 kg / 12.2 lbs
Boxed: approx. 10.5 kg / 23.1 lbs

What are the differences between the ISA428 and the ISA428 MkII?

It should come as no surprise that some features of the original ISA428 have been removed to offer the ISA428 MkII at such a competitive price. However, it is important to note that the analog circuit board used in the ISA428 MkII is exactly the same as used in the original. Internal tests we conducted on the new model suggest that interference in the audible frequency range has even been reduced compared to the original.

Here is a summary of the changes made to the new ISA428 MkII model compared to the original:

    
• The analog ‘moving coil’ peak meters have been removed.
      On the ISA 428 MKII, the LED meters remain and, in the signal chain, are located before the A-D converter, allowing for precise metering before conversion.
    
• The Soft Limiter function has been removed.
      Previously, a soft limiter was available to compress signals before the A-D converter inputs, reducing the chances of digital clipping. Without this limiter, the user only needs to monitor signal levels as they would on any other AD converter to avoid clipping and preserve audio quality. This brings the ISA428 MkII in line with the ISA828, which never had optical soft limiters.  
    
• The bit resolution selection button has been removed from the front panel.
      The ability to change the bit resolution for the A-D converter was a useful feature when the ISA 428 was first introduced to the market. Since then, technology has moved forward and the majority of users (if not all) now prefer to use dithering algorithms within their digital audio workstations for this purpose. The ability to change the bit resolution is actually still available via a jumper setting in the hardware on the A-D converter board. However, to achieve the highest audio quality, it is recommended to convert to the highest available bit resolution (24-bit). If a lower resolution is needed, good quality dithering, to be used later in the signal flow, produces the best results.
    
• The linear power supply has been replaced with a switching power supply.
      Aside from cost savings, this change brings several advantages to the ISA428 MkII: firstly, heat output is significantly reduced, protecting not only the circuitry inside the ISA428 MkII, but also adjacent equipment in the studio. The new power supply automatically switches input voltages. It can be connected to almost any power grid in the world without having to change the voltage selector or a fuse. The weight has also been greatly reduced: an important aspect for touring engineers and musicians. While some believe that linear power supplies are indispensable in audio equipment, the truth is that the switching power supply offers significant advantages in terms of convenience and reliability while maintaining very similar audio specifications to the original unit.

Drum tutorial recording

In the studio with "The Naked and Famous"