The ISA 430 MkII represents the pinnacle of Focusrite’s analogue channel strip technology, bringing together all the classic designs in one comprehensive production tool. Augmented with additional features and flavours, alongside unmatched internal routing and connectivity, the ISA 430 MkII enables today’s recording professional to enjoy the unique sonic contribution of these heritage designs within one extremely versatile processor. With the Producer Pack, Focusrite’s iconic status as the leading manufacturer of channel strips remains unrivaled.
From mic impedance switching and ‘mic air’ effect (a wire-wound inductor for increased spaciousness), to three compressor options (VCA, Vintage Opto and Opto Limit) combined with the compressed/uncompressed ‘Blend’ feature, the ISA430 MkII delivers a impressive variety of processing sounds.
Routing and monitoring flexibility has also received a booster. The unique ‘Listen’ feature (allowing you to hone in on the frequency you wish to affect) is now available on compressor, gate, and expander circuits as well as the ISA 430 MkII’s unique phase cancellation-based de-esser circuit. In addition, monitoring and inserts are available at a variety of points along the signal chain. Finally, the ISA 430 MkII features an optional 24bit-192kHz high performance (122dB A-weighted with jitter below 20 pico seconds) stereo A-D converter, allowing you to retain every nuance of your analogue signal as you flow seamlessly into the digital domain.
Focusrite EQ :
The Focusrite design for the original ISA110 EQ was commissioned as a custom rack for Air Montserrat, and later at George Martin’s personal request, for the custom Neve at Air London, (these units are still working at Air Lyndhurst today.) But what makes the Focusrite EQ so special?
The design, like most great designs, is relatively simple; a classic six band EQ, with shelving high and low bands, parametric low mid and high mid bands, and low and high pass filters. The HF and LF shelving EQ’s are unique – they are an implementation of the legendary Baxandall circuit designed in the 1950’s. The EQ is inherently expensive to build as a circuit; most typical shelving filters are variable resistance, fixed capacitance, but the design featured instead variable resistance for gain and variable capacitance for frequency. The positive benefit of this high-end design is that there is no interrelation between EQ bands, (making a change to one band has zero effect on another band,) and that the EQ is virtually noiseless.
The HF and LF EQ features switched capacitor circuits, rather than a variable resistor circuit. (The shape of the shelving filter in the case of a variable resistor circuit varies according to the frequency, thus shelving response is not pure, it’s shallow at one point, steep at another.) With the ISA 110, this switched capacitor circuit means the Q is constant, and the EQ slope is constant, meaning accurate, predictable, beautiful results.
The high-mid and low-mid EQ bands are fully parametric, and are a full implementation of the state variable circuit configuration – separate amplifiers for the Q, and for low-mid/high-mid gain. The usual cheap way to simulate this is to implement a compromise – a gyrator mid-band peaking circuit – but cutting corners in this way invariably means a poor imitation of the real thing. The Focusrite way has, from the beginning, been to choose the solution that sounded best then minimize cost through elegant design.
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 ISA430 MkII Features :
- ISA-series transformer based preamp - Featuring mic impedance switching and unique ‘mic air’ effect (a wire-wound inductor for increased spaciousness).
- Dual topology compressor - The ISA 430 MkII is the first ISA to feature both the classic transparent VCA circuit, and a vintage optical circuit with both soft compression and crunch settings.
- Unmatched flexibility - The ISA 430 Mk II features an incredible variety of insert points and variable signal path arrangements. It can operate as four independent modules!
- Precision VU metering at multiple points - Including input level, Insert 1 or 2 Return level, Compressor gain reduction or Sidechain listen level (switched).
- Classic Focusrite EQ design - an expanded version of the original ISA 110 with two additional shelving positions.
- Gate and Expander - Proprietary Focusrite discrete Class A VCA Gate and Expander designs, now both featuring a 'Listen' option for precision control.
- De-esser featuring 'De-ess Listen' - A combination of EQ and phase cancellation are used to create a smoother and less obtrusive result.
- Optional Strereo 192kHz ADC - Embodies cutting-edge conversion technology, incorporating Focusrite analogue circuitry to deliver A/D conversion of the highest quality (120dB Dynamic range).
