Focusrite ISA 430
Three rack spaces that hold an entire console strip - preamp, EQ, dynamics, de-esser, and limiter in one Class-A box.
Overview
The ISA 430 Producer Pack does the work of four separate pieces in one channel. Focusrite built it as a single-channel processor combining a preamp, EQ, compressor, gate, de-esser, and limiter. The company's own literature describes the circuit topology as Class A, derived from the Focusrite Studio Console and the Red Series processors. That lineage claim is marketing, but it shows where the designers thought they were aiming.
Start with the preamp. Balanced XLR connectors on the rear handle mic and line level. There are ¼-inch instrument jacks on both the front and rear panels, so a guitarist can plug in at the front and leave the back of the rack patched. Stepped knobs set mic gain from -60 to +6 dB in 6 dB increments, and line gain from -18 to +18 dB. A trim control adds variable gain on top of the stepped settings. The stepped approach is deliberate: you get repeatability over sweepability, so a setting from last Tuesday is easy to find again.
The dynamics section is flexible in practice. The compressor carries ratio, threshold, attack, release, and makeup gain controls. The gate offers variable threshold, release, attenuation range, and hold, and it switches to an expander at the touch of a button. Both the compressor and the expander/gate have their own ¼-inch sidechain inputs, so external keying works on both.
The EQ has four parts: wideband high- and lowpass filters, high and low shelving filters with adjustable rolloff frequencies, and a 2-band parametric EQ. You can also reorder the signal path. The dynamics and EQ sections can be switched in position relative to each other, and the insert can be placed before, between, or after the dynamics and EQ sections. The insert send and return jacks are balanced XLR.
Focusrite rates the ISA 430's frequency response at 20 Hz to 22 kHz, THD at 0.003% at 0 dBu, and noise at -96 dBu. Those are clean numbers for a Class-A transformer-coupled design. The optional digital I/O card is a $499 addition, factory- or dealer-installed, and it brings the unit into the digital domain.
Mix (December 2001, p.133) listed the ISA 430 among its nominees, and the same issue's coverage describes the shelving EQ with switched frequencies and the compressor and gate sidechains — the features that defined the box in the period press. EQ (February 2002, p.39) framed the ISA 220 Session Pack as drawing on the "award-winning ISA 430," which is a useful reminder that the 430 was the flagship the rest of the ISA line was measured against. The 430 also turns up in working-studio inventories of the period: Canadian Musician (undated issue, p. unknown) listed a Focusrite ISA 430 Producer Pack in one engineer's rack described as a "Swiss Army knife" of pre/compression/limiting/EQ/de-essing — the kind of shorthand that tells you how owners actually used it.
Two of the 3U rack-mountable units can be linked for stereo operation, which suits a stereo source or matched processing across a pair. Plan the rack accordingly, because each one takes 3U.
A later revision, the ISA 430 MK II Producer Pack, is a different product and should not be conflated with the original. Focusrite's own copy describes the MK II as adding a multi-format compressor, switchable impedance and mic AIR, enhanced listen capabilities, expanded routing, and 192 kHz conversion. Those are MK II features. The original 430 as documented here has the fixed-impedance preamp, the four-part EQ, the compressor/gate/expander, the de-esser, the limiter, and the optional $499 digital card. That's the box this page covers.
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