Focusrite ISA Two is a premium quality transformer-based preamplifier, featuring the specific ISA sound, variable impedance, 2 channels, and a variable high-pass filter:
Lundahl LL1538 Microphone Input Transformer
The Lundahl LL1538 transformer was chosen by Rupert Neve for the ISA 110 and to this day, this transformer remains among the best on the market and is used in every microphone preamplifier in the ISA series. Additionally, Rupert Neve has perfected the Zobel network in the ISA circuit, allowing the preamplifier to maintain an extremely flat frequency response over a wide bandwidth.
Gain of up to 80dB
ISA Two offers clean, distortion-free gain of up to 80 dB. The specific topology ensures low noise even at high gain levels. The transformer alone provides 20 dB of gain, while the ISA input stage adds another 60 dB.
Variable Input Impedance
ISA Two allows selection between 4 input impedances to match the microphone's impedance, thereby optimally revealing the microphone's characteristics. Among the impedance values, you can also select the value from the original ISA 110. The impedance can be selected via a switch on the front panel, and the selection is remembered even if the preamp is turned off and on again.
User-Calibrated Display
Each channel has an 8 LED strip for signal level display. You can align the analogue levels with the converters or DAW using the calibration knob on the rear panel.
Instrument and Line Inputs
ISA Two features 2 1/4" jack connections on the front panel for instruments with DI, and on the rear panel, it has 2 TRS inputs.
Variable High-Pass Cut Filter
To filter out low frequencies, ISA Two is equipped with an 18dB/octave high-pass filter, identical to that on the ISA 110. This can be adjusted via a large illuminated knob on the front panel and has a range of 16 - 420Hz.
Inserts
Each channel has a balanced 1/4" TRS insert. With input and output connections, a signal processor can be connected, which can be turned on and off via a switch on the front panel.
Specifications:
- front panel / channel:
- 1/4" jack instrument input
- impedance selector (Low, ISA 110, Medium, High)
- input selector: microphone, line, instrument
- gain switch: 0 - 30 dB/30 - 60 dB
- phantom power switch
- phase reverse switch
- gain knob: 0 - 60 dB in 10 dB steps
- continuously variable trim 0 ~ +20dB
- high-pass filter knob
- insert switch
- 8 LED display
- rear panel / channel
- XLR female microphone input
- 1/4" TRS line input
- send 1/4" TRS
- return 1/4" TRS
- XLR male line output
- signal display calibration knob
- dimensions: 480 x 280 x 44 mm, 1 rack space
- weight: 3.7 kg
Measured Performance:
- maximum output level: +24 dBu with THD+N < 0.01% at 1kHz measured with 150 Ω source impedance and 22Hz/22kHz band-pass filter
- maximum input level of the microphone transformer: +7 dBu with THD+N < 0.7% at 1kHz measured at 0 dB gain with 150 Ω source impedance and 22Hz/22kHz band-pass filter
Microphone Input Response:
- gain range: 0 dB to +60 dB in 10 dB steps, plus 0 dB to +20 dB continuously variable trim
- selectable input impedance:
- Low: 600 Ω
- ISA 110: 1.4 kΩ
- Medium: 2.4 kΩ
- High: 6.8 kΩ
- equivalent input noise: -127 dB
- noise: -97 dBu
- signal-to-noise ratio: 121 dB relative to maximum output +24dBu
- THD: less than 0.0007% at 1 kHz
- frequency response:
- at minimum gain 0 dB: -0.5 dB at 10 Hz, -1 dB at 135 kHz, relative to 1 kHz
- at gain +60dB: -6 dB at 10 Hz, -1 dB at 115 kHz, relative to 1 kHz
Line Input Response:
- gain range: 20 dB to +10 dB in 10 dB steps, plus 0 dB to +20 dB continuously variable trim
- input impedance: 10 kΩ from 10 Hz to 200 kHz
- noise: -97 dBu
- signal-to-noise ratio: 121 dB relative to maximum output +24dBu
- THD: less than 0.002% at 1 kHz
- frequency response at minimum gain 0 dB: -0.3 dB at 10 Hz, -1 dB at 80 kHz, relative to 1 kHz
Instrument Input Response:
- gain range: +10 dB to +40 dB continuously variable trim
- input impedance: > 2 MΩ
- noise: -95 dBu
- THD: less than 0.0007% at 1 kHz
- frequency response:
- at minimum gain +10 dB: -0.1 dB at 10 Hz, -1 dB at 115 kHz, relative to 1 kHz
- at gain +40dB: -2.5 dB at 10 Hz, -1 dB at 110 kHz, relative to 1 kHz
