Focusrite ISA428 MkII Mic Preamp


The Focusrite ISA428 MkII Mic Preamp provides four of Focusrite’s prestigious transformer based microphone preamps. It features the same classic circuitry and renowned audio quality found in the original at a new level of affordability. With switchable input impedance, direct instrument inputs and an optional eight channels of high quality analogue to digital conversion, the ISA428 MkII creates the perfect front end for the discerning recording professional.

First introduced in 1985, the ISA microphone preamp holds a reputation for outstanding transparency along with subtle warmth contributed by transformer core saturation. The addition of a variable impedance circuit allows ISA users to perfectly match the preamp with any microphone, or to use different settings creatively to shape the sound of the microphone. Unchanged for decades, the ISA microphone preamp topology offers incredible clarity and the signature Focusrite sound that makes it the top choice among many audio professionals today.

The optional class-leading ISA828 eight channel analogue to digital converter is also compatible with the ISA428 MkII. Along with the four mic preamp inputs, four additional inputs allow you to route other line signals through the converter.  High quality Burr-Brown Pro Audio Amplifiers and flagship PCM4220 A-D converter chips seated within Focusrite custom analogue circuitry deliver unparalleled performance. Specifications include a dynamic range of 122dB and jitter performance below 250 picoseconds. The card can be retrofitted at any time. Thanks to its convenient 25-pin D-Type connector, it integrates seamlessly with Pro Tools HD, as well as other digital workstations and mixing desks.

Four Instrument inputs, instantly accessible on the front panel, allow quick and easy connection without the need for a separate DI box. Extra processing can be placed between preamp and conversion via the units dedicated insert points, featured on every channel. Finally, accurate six-segment LED metering is designed to catch even the fastest transients on every channel.

Over 25 years, Focusrite has earned a reputation for bringing superb audio quality and engineering excellence to an array of audio professionals. Whether you’re looking to preserve the sound of your classic microphones, or searching for the perfect front end for your digital studio, the Focusrite ISA428 MkII Mic Preamp brings legendary tools to your studio at an exceptional new price.

Focusrite ISA428 MkII Mic Preamp Features:
-Four ISA-series transformer-based pre-amps - Over the past three decades, ISA mic preamps have contributed to many of the world’s
  most significant albums.
-Eight Channel optional A/D converter with 122dB dynamic range - The same cutting-edge analogue to digital converter card used in the
  ISA828. Four additional ADC inputs allow eight channels of high quality conversion.
-Switchable Impedance - Ideal for mic matching or extended microphone creativity. Settings include the ‘Vintage ISA110’ setting, providing
  the original Focusrite signature sound.
-Four front panel instrument inputs - Instant access on the front fascia - no separate DI box required.
-Dedicated analogue insert points - Switchable insert points are featured on every channel, allowing routing (between pre-amp and output)
  to additional external processing.
-Variable high pass Focusrite filter - Provided on every channel, this is the same filter as featured on the original ISA110 and the legendary
  Focusrite forte console.
-Accurate LED meters for every channel - Clear metering designed to catch even the fastest and most elusive of transients.

What’s the difference between ISA428 and ISA 428 MkII?
It should not come as a surprise that a few features found on the original ISA428 had to be removed in order to offer the ISA428 MkII at such a competitive price. It is important to note however, that the analogue circuit board used in the ISA428 MkII is exactly the same board used in the original. Our internal testing of the new model suggests that interference in the audible range may even be reduced from the original.

Here is a summary of the changes made to the ISA428 MkII:
-Analogue ‘moving coil’ peak meters have been removed - The LED meters remain on the ISA428 MkII and sit in the signal chain before the
  A-D converters, allowing for accurate metering during conversion.
-The Soft Limiter feature has been removed - Previously, the soft limiter was available to compress signals before they entered the A-D
  converter inputs, reducing the chances of digital clipping.  Without this limiter, users simply need to monitor signal levels as they would
  any other analogue to digital conversion in order to avoid clipping and maintain audio quality. This brings the ISA428 MkII in line with the
  ISA828 which has never featured the optical soft limiters.
-The bit depth selection button has been removed from the front panel - The ability to easily change the A-D converter bit depth was a
  useful feature at the time the original ISA428 was released. Since then however, technology has moved forward and most (if not all)
  users would prefer to use dithering algorithms within their digital audio workstation for this purpose. The ability to change the hardware
  bit depth is in fact still available as a hardware jumper setting on the A-D converter board. However, for the highest digital audio quality,
  in most cases it is recommended that users convert at the highest bit depth available (24-bit). If a lower bit depth is required, good quality
  dithering as late as possible in the workflow generally produces the best results.
-The linear power supply has been replaced with a switched-mode power supply - Aside from cost savings, this change brings some very
  welcome changes to the ISA428 MkII: First, heat output is significantly reduced, protecting not only the circuitry inside the ISA428 MkII,
  but also surrounding equipment in the studio. The new power supply automatically switches between input voltages. It can be plugged
  into most mains power supplies around the world without changing a voltage selector or a fuse. Weight is also reduced significantly –
  great for touring engineers and musicians.

Although there are some who believe linear power supplies are indispensable in audio equipment, the truth is that the switched mode power supply provides significant benefits in terms of convenience and reliability while maintaining audio specs very close to the original unit.

Focusrite ISA428 MkII Mic Preamp Specifications:
-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 103kHz
  -Gain range: 0dB to +60dB in 10dB steps, plus 0dB to +20dB continuously variable trim
  -Maximum headroom: +7.4dBu
  -THD+N: 0.0009% (measured at 1kHz -20dBu input signal, at 30dB gain setting, with a 20Hz/22kHz bandpass filter)
  -Noise EIN: -126dB (measured at 60dB of gain with 150ohm termination and 20Hz/22kHz bandpass filter)
  -Noise at main output with unity gain: -98dBu (measured with a 20Hz/22kHz bandpass filter)
  -SNR: 123dB (relative to max output 25dBu)
  -SNR: 120dB (relative to 0dBFS (+22dBu)
  -CMRR: 88dB. Input Impedance, variable as follows:
    -Switched Impedance setting:  Low        Equivalent Input Impedance at 1kHz:  600ohm
    -Switched Impedance setting:  ISA110   Equivalent Input Impedance at 1kHz:  1400ohm
    -Switched Impedance setting:  Medium  Equivalent Input Impedance at 1kHz:  2400ohm
    -Switched Impedance setting:  High        Equivalent Input Impedance at 1kHz:  6800ohm
-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 continuously variable trim
  -Maximum headroom: +25.4dBu
  -THD+N: 0.002% (measured with +4dBu input signal, 0dB gain setting, with a 20Hz/22kHz bandpass filter)
  -Noise at main output with unity gain: -91dBu (measured with a 20Hz/22kHz bandpass filter)
  -SNR: 116dB (relative to max output 25dBu)
  -SNR: 113dB (relative to 0dBFS +22dBu). Input Impedance: 10kohm
-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 –20dBu input signal, at minimum gain (+10dB), with a 20Hz/22kHz bandpass filter)
  -Noise at main output with minimum gain (+10dB): -95dBu (measured with a 20Hz/22kHz bandpass filter)
  -Input Impedance = >1Mohm
-High Pass Filter
 -Roll off = 18dB per octave 3 pole filter
  -Frequency range: 16Hz to 420Hz (continuously variable, measured at the 3dB down point)
-Meters
  -6 LED meter is calibrated 0dBFS = +22dBu (the maximum level which can be correctly converted by the optional internal A/D converter
    before overload occurs). The meter calibration points are as follows:
    -Meter panel calibration value in dBFS:  0dBFS      Equivalent dBu value:  +22dBu
    -Meter panel calibration value in dBFS:  -2dBFS     Equivalent dBu value:  +20dBu
    -Meter panel calibration value in dBFS:  -6dBFS     Equivalent dBu value:  +16dBu
    -Meter panel calibration value in dBFS:  -12dBFS    Equivalent dBu value:  +10dBu
    -Meter panel calibration value in dBFS:  -18dBFS    Equivalent dBu value:  +4dBu
    -Meter panel calibration value in dBFS:  -42dBFS    Equivalent dBu value:  -20dBu
-Front and rear connectivity
  -Analogue Channel Inputs (Inputs 1-4)
  -4 instrument 1/4" TS jack inputs on front panel
  -4 microphone XLR inputs on rear panel
  -4 line 1/4" TRS jacks on rear panel
  -4 insert return 1/4" TRS jacks on rear panel
  -4 ADC XLR inputs on rear panel
-Analogue Audio Outputs (Outputs 1-4)
  -4 line XLR outputs on rear panel
  -4 insert send 1/4" TRS jacks on rear panel
-Other I/O
  -IEC power input connector 100Vac – 240Vac
-Front Panel Indicators
  -8 output meters 6 segment
  -4 30-60 mic gain range selection indicator
  -4 +48V phantom power indicator
  -4 Phase indicator
  -4 Insert In indicator
  -4 Filter In indicator
  -4 Input selection indicators (Mic, Line, Inst)
  -4 Z In microphone input impedance selection indicators (Low, ISA110, Med, High) Clock select 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. 480mm x 88mm x 280mm
  -Boxed: approx. 620mm x 460mm x 210mm (24.4 x 18.1 x 8.3 inches)