Focusrite ISA One

The ISA One microphone preamplifier delivers Focusrite’s prestigious ISA transformer-based preamp in a rugged and portable chassis, at a groundbreaking price.

ISA One features the classic vintage microphone preamplifier topology from the original ISA110 module, which formed the cornerstone of each channel of Focusrite’s legendary Forté console.

The preamp is complemented by a line input 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 preamp with any microphone. ISA One also features an insert point, should the need arise to place extra processing between the preamp 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 Avid’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 MkII).

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
• 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
• 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)

Line Input Response

• Gain range = -20dB to +10dB in 10dB steps + 20 dB of variable gain
• Input Impedance = 10k? 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 than1M
• Low =greater than 300k
• 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
• 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