Focusrite ISA428 MKII Preamp


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Product Code: 6517-Standard
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The Focusrite ISA428 MKII Preamp provides 4 of Focusrite’s prestigious transformer-based mic preamps. It features the same classic circuitry and renowned audio quality found in the original at a new level of affordability. With selectable input impedance, direct instrument inputs and an optional 8 channels of high quality AD conversion, the ISA428 MKII creates the perfect front end for the discerning recording professional.

The Focusrite ISA428 MKII Preamp incorporates four of Focusrite's renowned mic pres in a simple-to-operate 2U enclosure, placing four mic preamps, instrument inputs and line inserts at your fingertips. The original Focusrite mic pre was designed to suit the microphones of the time; today's model makes one small change, adding three additional input impedances to the classic ISA 110 setting, allowing you to match any microphone, old or new, and access a wide range of sounds, from the character and warmth of a vintage mic to the clear transparency of a modern design.

Each mic pre has the option of mic, line or the front-panel instrument input, with variable input impedance to ensure you are getting the best performance from the source. Up to 60dB of gain is available on the four-position rotary and gain range switches, with a further +20dB of continuously variable trim, meaning a huge 80dB of gain is available should it be required. The high-pass filter features variable cut-off frequency between 16 and 420Hz. An array of 6-segment LED meters show peak signal level for the four mic pres, in addition to the four direct inputs to the optional A-D card. Switchable rear-panel insert points allow the use of inline processors such as compression.

Focusrite ISA428 MKII Preamp Features

  • Classic ISA mic preamp design featuring Lundahl LL1538 input transformer
  • Instrument and line inputs with dedicated input connectors and front-panel switch
  • Switchable input impedance including classic ISA 110 setting
  • Variable cut-off frequency high-pass filter
  • Dedicated switchable insert point
  • Per-channel six-segment LED peak-level meters
  • Optional A-D card with up to 192kHz, 24-bit sampling via ADAT or AES3

Focusrite ISA428 MKII Preamp Specifications

  • Mic Inputs:
    • Frequency Response at Minimum Gain (0dB) (Mic): -0.35dB at 20Hz and –3dB at 122kHz
    • Frequency Response at Maximum Gain (60dB) (Mic): –2.5dB at 20Hz and –3dB 103kHz
    • Gain Range (Mic): 0dB to 60dB in 10dB Steps, Plus 0dB to 20dB Continuously Variable Trim
    • Maximum Headroom (Mic): 7.4dBu
    • Noise EIN (Mic): -126dB (Measured at 60dB of Gain with 150 ohm Termination and 20Hz/22kHz Bandpass Filter)
    • Noise at Main Output with Unity Gain (Mic): -98dBu (Measured with a 20Hz/22kHz Bandpass Filter)
    • SNR (Mic): 123dB (Relative to Max Output 25dBu) 120dB (Relative to 0dBFS ( 22dBu)
    • CMRR (Mic): 88dB
    • Input Impedance, variable (Mic): 600 ohm, 1400 ohm, 2400 ohm, 6800 ohm
  • Line Inputs:
    • Frequency Response at Unity Gain (0dB) (Line): -0.3dB at 20Hz and –3dB at 94kHz
    • Gain Range (Line): -20dB to 10dB in 10dB Steps, Plus 0dB to 20dB Continuously Variable Trim
    • Maximum Headroom (Line): 25.4dBu
    • THD N (Line): 0.002 (Measured with 4dBu Input Signal, 0dB Gain Setting, with a 20Hz/22kHz Bandpass Filter)
    • Noise at Main Output with Unity Gain (Line): -91dBu (Measured with a 20Hz/22kHz Bandpass Filter)
    • SNR (Line): 116dB (Relative to Max Output 25dBu) 113dB (Relative to 0dBFS 22dBu). Input Impedance: 10k ohm
    • Frequency Response at 10dB Gain (Instrument): -0.2dB at 20Hz and 0dB at 200kHz
    • Frequency Response at 40dB gain (Instrument): -3dB at 20Hz and –3dB at 38.4kHz
  • Instrument Inputs:
    • Gain Range (Instrument): 10dB to 40dB Continuously Variable
    • Maximum Headroom (Instrument): 11.5dBu
    • Noise at Main Output with Minimum Gain (10dB) (Instrument): -95dBu (Measured with a 20Hz/22kHz Bandpass Filter)
    • Input Impedance (Instrument): >1M ohm
  • High Pass Filter:
    • Roll Off: 18dB Per Octave 3 Pole Filter
    • Frequency Range: 16Hz to 420Hz (Continuously Variable, Measured at the 3dB Down Point)
  • Front and Rear Connectivity:
    • 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 100V AC – 240V AC
  • Weight and Dimensions:
    • Weight: 5.5kg (12.2lbs)
    • Dimensions: 480mm (W) x 88mm (H) x 280mm (D)

Focusrite ISA428 MKII Preamp Includes

  • Focusrite ISA428 MKII Preamp
  • IEC Power Cable
  • User Guide
  • 2 Year Warranty

2 Reviews Hide Reviews Show Reviews

  • 5
    ISA 428 MKII
    Joel Schwamburger

    I recently upgraded from some lower end preamps and added the ISA 428 MKII. The sonic quality of the 428 is amazing. The unit has tons of clean gain. I don't experience the harshness or thin caracter that seemed to be the norm with my previous units. I absolutely love the sound when plugging in direct. On Bass the unit has a wonderful transparent and full frequency response with a nice touch of mid range warmth and definition. I also love it on drums and acoustic. I love using the ISA for summing. It sounds fantastic and with the inserts on each channel I can still use my outboard gear while utilizing the ISA's digital converters which sound way better than the stock converters on my interface. The only drawback for this unit is I wish Focusrite would have kept the Vu metering like on older 428 models but overall for the price you'll be hard pressed to find another 4 channel pre with this many features that sounds this good.

  • 5
    focusrite isa428
    richard yang

    great product! this was my second high end mic pre after an ssl alpha vhd. both of the products i love, as much as i am in love with my 2 chameleon labs 7622's. this is a great 4 channel solution for anyone that needs a tremendous amount of versatility to their setup. the variable impedance is a miraculous addition. it made an sm58 sound great! the unit is well laid out for all of the options each channel has and although the meters are a bit slow, are fairly accurate. not as aggressive as my ssl and not as punchy as my CL's, the isa428 is middle ground with it. a slightly colored sound with a warm touch, the tone is solid with a full midrange. this is my first choice for cymbals. it has become my go to pre for overheads and close mic'd ride and hi hats. i use moderately priced condensers for this application: adk sl pair and rode nt5 pair. both are fairly bright mics and the isa428 warmed them up and made them sound incredibly sweet. a high class pre.

What We Think


The Focusrite ISA One Preamp was my first outboard/standalone microphone preamp and I still use it to this day. The ISA 428 MKII is a four channel version so it's four times as awesome! It’s got such a clean and open sound to it, it’s one of my go-to preamps for vocals and acoustic guitar. This ISA 428 MKII gives you impedance options on the front that allows you to switch up the sound a bit and find the right fit for your microphone or sound source. The instrument input sounds great too, I love recording direct bass and guitars through it. With the four channels this unit provides, I'd highly recommend it for a drum kit. Kick, snare, and both overhead mics sound great through this unit. Check out the Focusrite ISA 428 MKII, you won’t be disappointed.

Wes DeLoach, Pro Audio Sales

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