Focusrite ISA One

Focusrite ISA One Description

The ‘ISA One’ microphone pre-amplifier delivers Focusrite's prestigious ISA transformer-based pre-amp in a rugged and portable chassis, at a groundbreaking price.

ISA One features the classic vintage microphone pre-amplifier topology from the original ISA110 module, including the Lundahl L1538 transformer and bespoke zobel network. (The original 110 pre amp formed the cornerstone of each channel of Focusrite's legendary Forte console.)

The pre-amp is complemented by a line input (XLR and TRS Jack) and an independent D.I. channel, complete with dedicated gain control, active or passive impedance switch, a TRS Jack output for routing to an amp and an independent XLR output on the rear. This flexible independent D.I. makes the ISA One ideal both for engineers wishing to blend a D.I.’d guitar signal with a mic’d guitar cabinet, and for demanding performers who require a single classic solution for both guitar and vocals.

A variable impedance circuit has been added, allowing the user to switch between four carefully selected input impedance settings. In addition to the original ISA110 impedance, three further impedance settings allow perfect matching, or creative mismatching of the pre amp with any microphone. ISA One also features an insert point, should the need arise to place extra processing between the pre amp or D.I. and the optional converter. Phantom power, phase reverse and a 75Hz, 18dB/octave high-pass filter are also available from the angled front fascia.

Independent input metering for both channels is provided in the form of a moving coil VU meter with variable calibration to suit analogue and digital recording media, alongside two six-LED peak meters; inputs can be metered either pre- or post-insert. The meter calibrations utilise all the same reference points as Digidesign's Pro Tools HD system, allowing effortless line-up.

ISA One’s headphone output features a dedicated volume control, which delivers an external stereo cue mix, (a simple click track, or a stereo mix feed from an interface or a live console,) fed to the headphones via two TRS jack inputs on the rear of the unit.

An optional state-of-the-art stereo A-D converter is also available (the same card as used with the ISA430 Mk II), embodying cutting-edge conversion technology seated within Focusrite’s custom analogue circuitry. This optional card can be retrofitted at any time and provides two channels of 24 bit/192kHz A-D conversion with a dynamic range of 119dB.

Key Features

• ISA Series Transformer-based Pre-amplifier - Encased in a rugged and portable chassis, ISA One offers the classic Focusrite microphone pre-amplifier at its lowest cost to date.
• Flexible Independent D.I. Channel - ISA One is ideal for both engineers and demanding performers alike, featuring independent gain control, an output for routing to an amp, an independent XLR output on the rear and routing to the optional ADC.
• Switchable Impedance - Choose one of four carefully selected input impedances, including the original ISA 110 setting, to suit any microphone.
• Optional Stereo 192kHz ADC - This optional card embodies cutting-edge conversion technology, incorporating Focusrite analogue circuitry to deliver the best A-D performance in its class (Dynamic range of 119dB).
• Rugged Custom Flight Case - Built to protect your ISA One from the rigors of the road. Rugged plywood construction with a solid polypropylene exterior and reinforced corners. Includes space to fi t cables and other accessories.
• Headphone Output with Volume Control - ISA One can feed either a sum of the two inputs to the headphones output, or an external stereo cue mix (such as a stereo mix feed from an interface) via two TRS Jack inputs on the rear of the unit.
• Dedicated Insert Point - Allows you to place extra processing between the pre-amplifi er or D.I. and the optional converter, such as an EQ or compressor.

Specifications

• Mic Input Response
  • Gain range = 0dB to 60dB in 10dB steps + 20 dB of variable gain
  • Input Impedance, variable as follows (Switched Impedance setting Equivalent Input Impedance at 1kHz):
    • Low = 600 Ohms
    • ISA110 = 1400 Ohms
    • Med = 2400 Ohms
    • High = 6800 Ohms
  • EIN (equivalent input noise) = -126dB measured at 60dB of gain with 150 Ohm terminating impedance and 22Hz/22kHz band-pass filter
  • Noise at main output with gain at unity (0dB) = -97dBu measured with a 22Hz/22kHz band-pass filter
  • Signal to noise ratio relative to max headroom (9dBu) = 106dB
  • THD at medium gain (30dB) = 0.0009% measured with a 1kHz -20dBu input signal and with a 22Hz/22kHz band-pass filter
  • Frequency response at minimum gain (0dB) = -0.5dB down at 10Hz and -3dB down at 125kHz
  • Frequency response at maximum gain (60dB) = -3dB down at 16Hz and -3dB down 118kHz
  • CMRR=98dB (Channel 1, 1kHz, maximum gain with +24 dBu input)
  • Crosstalk Channel to Channel: with 10dB@1kHz input to chA, chB output =104dBrA. With 10dB@10kHz input to chA, chB output = 84dBrA
• Line Input Response
  • Gain range = -20dB to +10dB in 10dB steps + 20 dB of variable gain
  • Input Impedance = 10kΩ from 10Hz to 200kHz
  • Noise at main output with gain at unity (0dB) = -96dBu measured with a 22Hz/22kHz band-pass filter
  • Signal to noise ratio relative to max headroom (24dBu)=120dB
  • Signal to noise ratio relative to 0dBFS (+22dBu) = 118dB
  • THD at unity gain (0dB) = 0.001% measured with a 0dBu input signal and with a 22Hz/22kHz band-pass filter
  • Frequency Response at unity gain (0dB) = -0.3dB down at 10Hz and -3dB down at 200kHz
• Instrument Input Response
  • Gain range = 10dB to 40dB continuously variable
  • Input Impedance:
    • High = greater than1MΩ
    • Low =greater than 300kΩ
  • Noise at minimum gain (+10dB) = -92dBu measured with a 22Hz/22kHz band-pass filter
  • Noise at maximum gain (+40dB) = -62dBu measured with a 22Hz/22kHz band-pass filter
  • THD at minimum gain (+10dB) = 0.001% measured with a 10dBu input signal and with a 22Hz/22kHz band-pass filter
  • Frequency Response at 10dB gain with -10dB input = 10Hz-100kHz +/- 0.6dB
  • Frequency Response at 40dB gain with -40dB input = -2.5dB down at 10Hz and 0dB at 100kHz
• High Pass Filter
  • Roll off = 18dB per octave 3 pole filter
  • Fixed Frequency 75Hz measured at the 3dB down point
• Meters
  • Moving coil (MC) meter is factory calibrated to 0VU = +4dBu with 1kHz sinewave. With the VU Cal button pressed the meter can be adjusted on the rear panel to allow 0VU to equal +10dBu to +26dBu with the centre detent being equal to +22dBu.
  • Peak LED meters calibrated in the detent position for 0dBFS = +22dBu, calibration is adjustable on the rear panel to allow 0dBFS to equal +10dBu to +26dBu
  • Routing for MC and Peak1 meter is after the HPF, pre insert send or switched post insert return. Peak2 is always pre ADC channel 2, which can be fed by external input or Instrument input.
  • LED levels are as follows when peak calibration is set to center detent on the rear panel. (This is when using the internal ADC).
    • 0 = +22dBu
    • -2 = +20dBu
    • -6 = +16dBu
    • -12 = +10dBu
    • -18 = +4dBu
    • -42 = -20dBu
• Front & Rear Connectivity
  • Analogue Channel Inputs:
    • Mic input: XLR x 1
    • Line input: XLR x 1 and TRS x1
    • Instrument input TRS Jack: XLR x 1
    • External ADC input: TRS Jack x 1
    • Return: TRS Jack x 1
  • Analogue Channel Outputs:
    • Send: TRS Jack x 1
    • Balanced line output: XLR x 1
    • DI output: XLR x 1
    • DI through: TS Jack x 1
  • Analogue Channel Additional I/O:
    • Cue mix left input: TRS Jack x 1
    • Cue mix right input: TRS Jack x 1
    • Headphones output: ¼” TRS Jack x 1

Reviewed in Music Planet:

More from Music Planet.