ISA Two

Specifications

Two channel classic Focusrite ISA transformer-based preamps

Front panel, per channel:

  • 1/4" instrument input
  • Variable input impedance - Low, ISA 110, Medium, High
  • Input selection - Mic, Line, Instrument
  • 0 - 30 dB/30 - 60 dB gain switch
  • Phantom power switch
  • Phase invert switch
  • 0 - 60 dB gain in 10 dB steps
  • 0 - +20 dB continuously variable trim
  • Variable high-pass filter with on/off switch
  • Insert point on/off switch
  • Eight-LED user-calibrated level meters
  • Single power switch

Rear panel, per channel:

  • XLR-F mic inputs
  • 1/4" TRS line inputs
  • 1/4" TRS Sends
  • 1/4" TRS Returns
  • XLR-M line output
  • Single peak meter calibration dial
  • Single IEC power socket

Measured Performance

Maximum Input and Output Levels

Maximum Output Level

+24 dBu with a THD+N < 0.01% at 1kHz measured with 150 Ω source impedance and 22Hz/22kHz band-pass filter

Maximum Microphone Transformer Input Level +7 dBu with a THD+N < 0.7% at 1kHz measured at 0 dB of gain with 150 Ω source impedance and 22Hz/22kHz band-pass filter

Mic Input Response

Gain range 0 dB to +60 dB in 10 dB steps, plus 0 dB to +20 dB continuously variable trim

Input Impedance

Switched Impedance setting
Equivalent Input Impedance at 1 kHz
Low = 600 Ω
ISA 110 = 1.4 kΩ
Med = 2.4 kΩ
High = 6.8 kΩ
EIN
(Equivalent Input Noise)
Measured at 60 dB of gain with 150 Ω
source impedance and 22 Hz-22 kHz band pass filter
-127 dB

Noise

Noise at output with unity gain (0 dB) and 22 Hz-22 kHz band pass filter -97 dBu

Signal-to-Noise Ratio

Measured with 150 Ω source impedance and 22 Hz-22 kHz band pass filter 121 dB relative to max output +24 dBu

Total Harmonic Distortion + Noise

Measured with a -20 dBu input signal at +30 dB of gain and with a 22 Hz-22 kHz band pass filter

< 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 +60 dB gain

-6 dB at 10 Hz,
-1 dB at 115 kHz, relative to 1 kHz

CMRR (Common Mode Rejection Ratio)

-94 dB for mic input at 60 Hz for max. output = +24 dBu
-91 dB for mic input at 10 kHz for max. output = +24 dBu

Crosstalk Channel to Channel

Mic input, with I/P = 0 dBu, gain = 0 dB @ 1 kHz input to channel A, channel B output = -85 dB

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

Noise at main output with gain at unity (0 dB) measured with 50 Ω source impedance and a 22Hz - 22 kHz band pass filter

-97 dBu

Signal-to-Noise Ratio

Measured with 50 Ω source impedance and a 22 Hz-22 kHz band pass filter

121 dB relative to max output +24 dBu

Total Harmonic Distortion + Noise

Measured with a 0 dBu input signal, +10 dB of gain and a 22 Hz-22 kHz band pass filter

< 0.002% at 1 kHz

Frequency Response

At unity gain (0 dB) -0.3 dB at 10 Hz,
-1 dB at 80 kHz, relative to 1 kHz

Crosstalk Channel to Channel

Line input, with I/P = 0 dBu, gain = 0dB
@ 1 kHz input to channel A

Channel B output
= -91 dB

Instrument Input Response

Gain Range

+10 dB to +40 dB continuously variable trim

Input Impedance

> 2 MΩ

Noise

>Measured with 22 Hz-22 kHz band pass filter Minimum gain (+10 dB) = -95 dBu

Frequency Response

At minimum gain (+10 dB)

-0.1 dB at 10 Hz,
-1 dB at 115 kHz, relative to 1 kHz

At maximum gain (+40 dB)

-2.5 dB at 10 Hz,
-1 dB at 110 kHz, relative to 1 kHz

High-Pass Filter

Roll-Off

18 dB per octave (3 pole filter)

Frequency Range

Continuously variable from 16 Hz to 420 Hz (-3 dB)

Weight and Dimensions

W x D x H

480 mm x 280 mm x 44 mm

Weight

3.7 kg