Overview
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.
The ISA Pre
The ISA microphone pre-amplifier was first introduced back in 1985. This transformer-based pre-amplifier formed the first half of the ISA110 mic-pre and EQ module on Focusrite's critically acclaimed Forte console. This console, and the later Studio console were hailed by many as the finest sounding consoles ever built.
The ISA microphone pre-amplifier went on to form the cornerstone of all ISA and RED Focusrite products. The topology has never changed, except for the addition of a variable impedance circuit, allowing ISA users to either perfectly match the pre-amp with any microphone, thus maximizing level, or to use different settings creatively to shape the sound of the microphone being used. The original ISA110 setting was supplemented by three further impedance settings.
The Focusrite pre amp is renowned for its transparency, but there's also that subtle warmth that transformer core saturation contributes. This seeming contradiction of warmth plus beautifully open, unrestricted high frequencies, is a classic hallmark of the mid 80's Focusrite designs.
With processors whose bandwidth is strictly limited to the audible (20Hz to 20kHz) bandwidth alone, significant roll-off can still occur, affecting the higher audible frequencies of the signal. Therefore, in order to capture every subtle nuance, exactly as it occurs whilst avoiding any roll-off, the pre-amp must operate over a far greater bandwidth. The extremely broad frequency response of Focusrite pre-amps - close to 200kHz at the top end - guarantees accurate phase response across the much narrower range of human hearing, the roll-off point being moved entirely outside of the audible hearing range.
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 AND 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
Weight
• 3.9kg
• 8.6Ibs
Dimensions
• 220mm (W) x 104mm (H) x 254 - 290mm (D - top to bottom)
• 8.66" (W) x 4.1" (H) x 10" - 11.4" (D - top to bottom)
Reviews
Musictech – Issue 64 – Jul ‘08 - Review Quotes
'This preamp is clean, pure, and transparent, but, like all fine preamps, it can make recordings sound better than ‘reality’.'
'With 80dB of available gain to play with just about any microphone you want and its neutral but ‘enhanced’ sound quality makes it a general-purpose tool rather than a preamp you can only use for those ‘special occasions’. It can also solve monitoring issues as well as providing a fully independent second channel for DI duties.'
'Some engineers maintain that the closer you can get the preamp to the mic the better, so in this respect the ISA One is ideal.'
'Why Buy? Pristine sound quality, Versatile connectivity, Impedence switching, Excellent metering, Huge gain level, Low noise, Onboard monitoring, and competitively priced.'
Amazona.de - German Webzine – Jul ‘08 - Review Quotes (Translated from German)
'All the Legendary superbness of an ISA for less than 1.000,-€ unimaginable to date.'
'Thanks to excellent technology and switchable impedance it's a perfect match to any mic.'
'Legendary, well engineered'
Soundcheck.de - German Webzine – Jul ‘08 - Review Quotes (Translated from German)
‘The ISA One emerges as a candid pre-amp which gains the signal in a natural way without changing the original character of the sound.’
‘In no time at all the ISA One is ready for use; it keeps all promises regarding sound. The results in recording session tests have produced crystal clear vocals, even with the proximity effect the sound is consistent and differentiated.’
‘The same can be said for the ISA Ones performance with acoustic instruments, guitars keep their natural brilliance in high frequencies and low frequencies remain firm and clear.’
‘Our overall impression of the ISA One is that it has a warm sound which stands head and shoulders above the rest of other audio interfaces for use with your computer.’
‘Focusrite's ISA-One is an all-round solution in the studio, which enhances every signal. Backside connections leave nothing to be desired and feature a connection to every plug in use.’
‘Thanks to a couple of options, all types of mics are realisable. The ISA One is unbeatable in use with different mics.’
Resolution - Volume 5 – Jul/Aug ‘08 - Review Quotes
'The look and feel of many of the front panel controls will be utterly familiar to anyone who has used other units in the ISA range, and the core of the unit is very straightforward.'
'The DI section remains active and has it's own dedicated balanced output on the rear of the unit. This means that a DI source could be recorded via this output, while the pass-through is sent to an amp. A mic on this amp could then run through the mic pre, which feeds its own, separate output. In this kind of situation, the metering provided is quite comprehensive.'
'In use, the sound of the unit will yield no surprises to anyone who has used other devices in the ISA range. The mic pre is quiet, clean and nicely neutral with just a touch of HF brightness.'
'The switchable input works well too, with the lowest settings able to pull some additional LF weights out of dynamic and ribbon microphones.'
'The DI stage impressed me as much as anything else - my current favourite is a Radial JDV, and the ISA Ones DI matched it in most respects.'
'As a solution to minimum signal path recording of guitars it works well particularly for recording both a DI and mic feed, and if you're short on decent headphone foldback amps, it has it's uses here too.'
