Focusrite ISA 8 Channel ADC for ISA428, ISA 428MkII & ISA828

The ISA eight channel 192kHz A-D converter outperforms every other converter yet devised, and is the first audio A-D converter to utilise Burr-Brown Pro Audio Amplifiers and flagship PCM4220 A-D converter chips. With cutting-edge conversion technology seated within Focusrite custom analogue circuitry, the card delivers unparalleled performance; specifications include a dynamic range of 122dB and jitter less than 250 picoseconds.

The card can be retrofitted to an ISA428, ISA428 MkII or ISA828 at any time and, thanks to its convenient 25-pin D-Type connector, integrates seamlessly with Pro Tools HD as well as other popular hard disk recorders and mixing desks.

All eight converters are always available with this option, even when using the ISA428 and ISA428 MkII. When installed in one of these four-channel mic preamps, the the extra 4 converters of the A-D card are fed by four XLR inputs on the back labeled "ADC Input".

Digital formats include an eight-channel single/dual wire AES/EBU and S/PDIF output, as well as an eight-channel ADAT lightpipe (SMUX/SMUX2) output. Word clock i/o is provided via dedicated BNC connectors.

Output formats (All channels)

• AES/EBU (5V / 110 ohms), S/PDIF (0.8V / 75 ohms)
• ADAT lightpipe (SMUX I/II/IV, channels 1-4 only in 176.4kHz, 192kHz mode)
• S/PDIF lightpipe (channels 1-4 only; mutually exclusive with ADAT lightpipe)

Bit depth

• 24 bits, internally configurable to 16 or 20 bits if necessary.

AES3 output jitter

• <:1500ps, 50Hz-100kHz
• <:350ps, 700Hz-100kHz

Frequency response

• All ranges: 20Hz-20kHz +/- 0.3dB (100Hz-20kHz +/- 0.1dB)
• 176.4kHz, 192kHz : 17Hz-90kHz +/- 0.5dB

THD+n

• -121.5dB A-weighted, audio band-limited, 1kHz, -60dB FS input
• Maximum 0.0033% at -1dB FS (1kHz)
• Minimum 0.0008% at -15dB FS (1kHz)

Idle channel noise

• 117.5dB at 44.1kHz, CCIR-weighted, full bandwidth

Crosstalk

• -100dB at 12kHz
• (paired channels)
• -95dB at 20kHz

Focusrite A-Ds

Just paying for the PCB and circuitry, without any additional casing and metalwork, affords a considerable reduction in cost whilst maintaining an extremely high level of sonic clarity. However, the benefits from installing Focusrite's optional ADC extend far beyond the obvious financial advantages and space saving issues. As most converters use the same chips, it is the quality of the surrounding analogue circuitry that makes the difference. This is the reason why the ISA ADC is unrivalled in terms of both price and performance.

Focusrite's R and D team have carefully considered the organisation of the PCB layout and grounding, ensuring that the S/N ratio and linearity of the converter are optimised. The noise floor and THD (Total Harmonic Distortion) are kept to a minimum by the nature of the power supply and the analogue input design, with analogue filtering positively effecting the sound of the digital noise.

In addition, the supporting circuitry around the ADC (dealing with data transmission, bit reduction and incoming word clock) has been carefully structured, as it influences the converter through heat, power supply and data jitter. One of the most important aspects of the ADC is the clock design, as this determines the linearity of the digital output. All Focusrite ADCs are designed to have incredibly low jitter figures (44.1kHz-192kHz < 20 psec) which significantly improve the quality of the sound.

With the converters housed within the analogue units, the signal path is kept as short as possible, having no unnecessary analogue connections to the inputs of recording equipment. In addition, Focusrite units do not contain extraneous clocks or other sources of digital noise, unlike so many digital desks and multi-I/O DSP configurations.