Focusrite ISA428

The ISA428 MkII four-channel mic preamplifier features four of Focusrite's transformer-based ISA preamps, as used in the orginial model and also found in the Forte console. Each channel has phantom power and phase-reverse controls, plus switchable input impedance and an adjustable high-pass filter.

The MkII model also has an optional eight-channel A-D converter upgrade, which converts signals from the preamps and an additional four line-level inputs to 24-bit digital data streams at sample rates of up to 192kHz. New to the ISA428 MkII is a switched-mode power supply, which lowers the internal noise and heat output of the unit, and greatly reduces its weight.

When designing the ISA428 MkII, the Focusrite R&D team sought to maintain the sound quality of its predecessor, but introduce it at a new level of affordability that appeals to a more diverse range of users. To that end, the same analogue circuit board can be found in both the original and MkII derivations of the ISA428.

The most noticeable difference is the removal of the large moving-coil peak meters of the ISA428. Metering duties on the MkII are handled by per-channel, six-step LED bargraph displays, which monitor the signal prior to the A-D stage, providing an accurate status of the output level. Also removed is the soft limiter feature of the ISA428. (Precise calibration figures are supplied in the user manual, to enable accurate system setup.)

Other features include: switchable input impedance to match different mics to the preamp (this includes an 'ISA110' setting to provide the sound of the Forte's ISA110 module); Hi-Z instrument inputs on each channel with jack sockets on the front panel; switchable balanced insert points, allowing additional hardware to be linked into the signal chain; and a variable high-pass filter to provide adjustable filtering of frequencies between 16Hz and 420Hz.

‘More and more people are making high-quality recordings outside the traditional studio environment, and they have different requirements to recording studios,’ says Focusrite’s Director of Product Strategy Rob Jenkins. They want the same high-quality audio, but in a simpler package. So the objective with the ISA428 MkII was to create a leaner, more cost-effective design that maintained the Focusrite sound. The new power supply helped us achieve this, and it actually runs cooler with less noise and interference than the previous model.’


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