The ISA828 eight channel microphone pre-amplifier provides eight original ISA transformer-based pre amps in a single robust 2U chassis, offering the Focusrite signature sound at its lowest cost per channel to date.
The eight ISA-series transformer-based microphone pre amps feature the same classic microphone pre-amplifier design as the original ISA110 module from Focusrite's critically acclaimed Forte console (including the original Lundahl L1538 transformer and bespoke zobel network).
The pre-amps are complemented by eight line inputs, eight line outputs and an optional eight channel 192kHz ADC boasting the widest dynamic range of any converter to date. Thanks to its convenient 25 pin D-Type connectors, the ISA828 also integrates quickly and seamlessly with ProTools HD, as well as other popular hard disc recorders and mixing desks.
The microphone input stage additionally includes a variable impedance circuit, allowing the user to switch between four carefully selected input impedance settings. The original ISA110 setting is supplemented by three further impedance settings 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 four front panel instrument inputs also feature high and low impedance options to provide a comprehensive and accessible DI solution. Insert switches are also featured on every channel, should the need arise to place extra processing between the pre amp and converter. Vintage design 75 Hz / 18dB per octave high pass filters are also provided on every channel, ensuring unwanted low frequencies are effectively eliminated.
The ISA828’s new optional eight-channel 192kHz ADC is the first audio ADC to utilise Texas Instruments Burr-Brown Pro Audio Amplifiers and Flagship Analog to Digital Converter PCM4220 chips. This cutting-edge technology is encompassed within Focusrite’s own custom analogue circuitry to provide eight channels of unparalleled A/D conversion, delivering a dynamic range of 122dB and jitter at less than 250 picoseconds.
Finally, every channel features a six LED input meter, complete with global precise meter trim. Metering has been designed to utilise the same reference points as Digidesign’s Pro Tools HD™ system and provides clear and accurate input metering, independent of the DAW.
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.
All critical inputs are transformer-coupled, providing a dual gain structure - an expensive option, but the optimum route to high quality signal handling. Focusrite use Lundahl LL1538 transformers.
Also originally employed was a 'Zobel network' to counteract the reactance of the primary coil of the transformer. A Zobel network is a damping circuit that is applied across the secondary of the mic input transformer. This damping network tailors the naturally occurring high frequency resonant point of the input transformer. The Zobel network featured in ISA and RED pre amps was set by ear, has never changed, and as such is a key contributor to the Focusrite sound.
Finally, all the components featured in the ISA pre-amp were always chosen with a specific frequency response in mind. Rather than accepting the effect of the components chosen, the designer worked diligently with the values of every component in a relentless effort to achieve the desired response.
Focusrite ISA828 Features :
- Eight ISA series transformer-based preamps - In a single robust 2U chassis, offering the classic Focusrite pre at its lowest cost-per-channel to date.
- New Optional Eight Channel 192kHz ADC - Embodies cutting-edge conversion technology, incorporating Focusrite analogue circuitry to deliver the best A/D performance on the market, bar none
- Convenient 25 pin D-Type connectors - The ISA828 integrates quickly and seamlessly with ProTools HD, as well as other popular hard disk recorders and mixing desks.
- Switchable Impedance - Selectable per channel; choose one of four carefully selected input impedances, including the original ISA110 setting, to suit any microphone.
- Direct Instrument inputs - Each instrument input features high and low impedance options to provide a comprehensive and accessible DI solution.
- Inserting available on every channel - Allows external devices to be inserted between the pre amp and the ADC, using the 25-pin D-type cable.
- High pass filter, Phase reverse and Phantom power - Each has a dedicated switch, independent on each channel.
- Six LED input meter - Complete with precise meter trim - Designed to utilise the same reference points as Digidesign’s HD.
