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Focusrite ISA Pre-amps – A Little Bit of Recording History

Posted on November 16, 2015 by Dan The Man There have been 0 comments


Focusrite is known today as a manufacturer of audio interfaces for computer recording, and many studio newbies won’t necessarily know what’s behind their current products in terms of audio technology and musical history. If you want to find out more about the Focusrite story, then read on…


Way back in 1985 (OK, it’s not that far back for some of us!), Rupert Neve, who had been designing world-class Neve recording consoles for many years, set up a new UK company, Focusrite. A certain Sir George Martin subsequently commissioned Rupert to build ‘no-compromise’ pre-amp and EQ console modules for the mixing console at AIR studios, Montserrat. This circuit design was then made commercially available with the introduction of the ISA 110, a rack-mount input stage that combined a transformer-coupled microphone amplifier and a classic Neve EQ stage, into one high performance unit. ISA simply stands for 'Input Signal Amplifier'.

With a cost-is-no-issue approach, Rupert and co. then set about producing the finest mixing console ever built, the Focusrite Forté, in the pursuit of audio perfection using the best components available. Unfortunately, this approach ultimately led to financial difficulties, and only a small handful were ever produced, with just two still in existence today.


The company was bought out in 1989, and although Rupert Neve had moved on to pastures new, his circuit designs lived on inside the incredible Focusrite Studio Console, of which only ten were made. These large format recording consoles were built exclusively for some of the best recording studios during the late 1980's and early 1990's. Over the years that followed, new ranges of outboard gear were then brought to market based on these designs, including the famous Red (studio), Blue (mastering) and Green (budget) series’.

The Studio Console, and the original Forte, were, and still are, considered by many as sonically the finest console ever built. In fact, the core modules from these consoles live on with Focusrite's current range of ISA products. These have in themselves also become recording classics, and the choice of the world's finest producers and engineers seeking that classic sound that lies behind a plethora of hit records.

What’s under the lid of a modern Focusrite ISA?

At the heart of the ISA range is an impeccably designed microphone preamplifier with a Lundahl 1538 input transformer – essentially the same circuit based on the original ISA110, that has been used for 30 years in successive Focusrite designs. The input transformer gives a special character to the sound that can’t be truly emulated in any other way: inseparable from the microphone itself, the transformer input stage is ideal for use with classic as well as modern microphones. Focusrite use this, and other tried-and-tested electronic wizardry to recreate what they call their ‘Heritage Sound’, and the Lundahl transformer really does add that ‘special something’ that allow producers to get the most out of their mic collection.

The modern incarnations of the ISA range have a twist that the original models didn’t have, which makes it far more versatile: selectable input impedances that allow you to match microphone to input in different ways. This feature can really bring out the character of a classic mic, or allows you to emphasise a specific feature, or to go for a totally transparent, modern sound.

The current line-up of Focusrite ISA modules opens the door for anyone to get the Focusrite Heritage Sound. There are various formats to choose from – 500 series, single, dual, quad and eight-channel pre-amps, and the ISA430 – a complete channel strip with compression, EQ, and an incredibly flexible channel path that is the modern equivalent of the ISA130 of yesteryear. All of the range use the Lundahl transformer, and all give that no-compromise studio-quality input to your recording system.




A portable, single channel desktop ISA preamp with switchable input impedance, independent DI input, headphone output, and optional A/D conversion.

ISA 430 MkII


Astonishingly versatile channel strip with EQ based on the original ISA110, both VCA and optical compression, expander/gate, extensive signal path i/o, plus optional A/D conversion



Dual-mono ISA microphone preamps in a 1u rack format. Perfect for stereo recording with two pristine variable impedance mic channels.

ISA 428 MkII


Four of those lovely variable impedance ISA preamps with DI inputs, plus optional A/D conversion

ISA 828


A whole bank of eight classic ISA microphone preamps with optional A/D conversion. Ideal for larger studio sessions and multi-tracking.

Red 1 500 Series Mic Pre


The original single-channel Red microphone preamp in a lunchbox format. The original Red range was launched in 1993 and was also based on the original ISA circuitry.



If you want to achieve the best possible recordings, you need the best possible input stage (plus  some good mic’s, top quality A/D conversion, good ears, and a decent sound source!). The Focusrite ISA gives you a major part of that at least - a low-noise, characterful and versatile microphone and instrument input.

If you are at the stage where you just can’t justify the price tag of an ISA pre-amp, then you can still get the Focusrite sound (albeit not of the ‘Heritage’ variety) with their Scarlett and Saffire ranges of audio interfaces, or consider stepping up to the Claret range for the best of all worlds when it comes to DAW recording.

This post was posted in Blog entries, General News, In-Depth Reviews, Product News, Recording and was tagged with focusrite, focusrite isa 428 mkii, focusrite isa828, isa, isa 1, isa 2, isa one, isa two