Focusrite 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.)
- 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).
- 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-amplifier or D.I. and the optional converter, such as an EQ or compressor.
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 utilize 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 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 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.