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Focusrite ISA428 Four Channel Preamp




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    Product Description

    The ISA preamp sound is quintessentially British, well-rounded, and with plenty of detail and punch. The Focusrite ISA sound can be heard on countless records made throughout pop & rock history.

    The ISA428 combines this timeless sound with contemporary features to meet modern demands. Rack form factor, clear metering and versatile controls/connectivity - all in one. And that's just getting started...

    Key features

    • 4 ISA Series transformer-based mic preamplifiers
    • Optional 8 channels of high-quality analogue to digital conversion
    • Classic ISA mic preamp design featuring Lundahl LL1538 input transformer
    • Switchable input impedance including classic ISA 110 setting
    • Variable cut-off high-pass filter
    • 6-segment user-calibrated LED meter per channel
    • Dedicated per-channel insert point
    • Optional AD card with up to 192kHz, 24-bit sampling via ADAT or AES3
    • 2U 19" rack-mount format

    Classic Neve-inspired Specs

    The ISA428 combines 4 independent classic ISA microphone preamps, taken straight from the original ISA 110 module. As mentioned earlier, the sound of this module has been a mainstay of contemporary music production for decades. 

    The addition of a Rupert Neve-specified input transformer - the Lundahl LL1538 - ensures that the impedance is matched with supreme accuracy. Not only that, but you can be confident of a noise-free, crystal-clear response. Many the LL1538 is widely considered to be "probably the best 1:5 microphone input transformer available."

    Versatile Modern Design

    Each of the 4 preamps have the options of mic, line or front-panel instrument input to suit every scenario. 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 offer razor-sharp performance seldom found at this price point. 

    A convenient 25-pin D-Type connector means seamless connectivity with DAWs, including Pro Tools. If that wasn't enough, you get a subtle but effective high-pass filter, with a variable cutoff frequency of 16-420Hz - a tonal control that can make a huge difference, particularly with vocal performance. 6-segment LED meters show peak signal levels in dBFS, while a real-panel control lets you tweak calibration to match your A-D converters. 

    The final touch is the addition of rear-panel insert points. Easily make use of inline processors like compression - a classic sound updated for the modern studio setup.


    Mic input response

    • Gain range: 0dB to +60dB in 10dB steps, plus 0dB to +20dB continuously variable trim
    • Noise EIN: -126dB (measured at 60dB of gain with 150 termination and 20Hz/22kHz bandpass filter)
    • Noise at main output with unity gain: -98dBu (measured with a 20Hz/22kHz bandpass filter)
    • 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
    • Input Impedance, variable: 600, 1400, 2400, 6800

    Line input response

    • Gain range: -20dB to +10dB in 10dB steps, plus 0dB to +20dB continuously variable trim
    • Frequency Response at unity gain (0dB): -0.3dB at 20Hz and -3dB at 94kHz
    • Input Impedance: 10k

    Instrument input response

    • Gain range: +10dB to +40dB continuously variable
    • Input Impedance (Instrument): 2 MO
    • Noise at main output with minimum gain (+10dB): -95dBu (measured with a 20Hz/22kHz bandpass filter)
    • 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

    High Pass Filter

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

    Meter panel calibration value in dBFS / Equivalent dBu value

    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)

    • 0dBFS / +22dBu
    • -2dBFS / +20dBu
    • -6dBFS / +16dBu
    • -12dBFS / +10dBu
    • -18dBFS / +4dBu
    • -42dBFS / -20dBu

    Front and rear connectivity

    • Analogue Channel Inputs (Inputs 1-4)
    • 4 instrument 14" TS jack inputs on front panel
    • 4 microphone XLR inputs on rear panel
    • 4 line 14" TRS jacks on rear panel
    • 4 insert return 14" 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 14" TRS jacks on rear panel

    Weight and dimensions

    • 480mm (W) x 88mm (H) x 280mm (D)
    • Weight: 5.5kg
    Analogue Inputs
    Trade Doubler Group ID
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    Andertons Music Company's Registered Office: 58-59 Woodbridge Road, Guildford, GU1 4RF. Andertons Music Company acts as a credit broker and not a lender and only offers credit products from Secure Trust Bank PLC trading as V12 Retail Finance. Andertons Music Company is authorised and regulated by the Financial Conduct Authority. Credit provided subject to age and status.