The ISA series by Focusrite offers some of the highest-quality microphone preamplifiers in the mid-priced range.
The history of this design begins in 1985, when Sir George Martin (known for his work with The Beatles) commissioned the legendary Rupert Neve to create a microphone preamplifier with as little added distortion and noise as possible.
Neve developed the ISA 110 (Input Signal Amplifier) — a preamplifier with a discrete design featuring a transformer-balanced input.
At the heart of this sound lies the Lundahl LL1538 input transformer — a key component in both the original design and the modern ISA models.
We typically describe ISA preamps as clean and transparent — and rightly so. However, when peak levels reach between 0 and 4 VU (+4 to +8 dBu), the input transformer begins to saturate, resulting in harmonic enrichment and soft knee compression. Of course, the effect is not as pronounced as in other Rupert Neve designs — for example, the legendary Neve 1073, known precisely for its characteristic drive.
In the video accompanying this article, we take an in-depth look at the Focusrite ISA One. Despite its name, it actually functions as a dual-channel preamplifier.
You will hear how, during the recording of a female pop/rock vocal with properly set levels, the saturation effect becomes noticeable only when the singer reaches a powerful high belt and the levels move into the “red zone.”
At the other end of the spectrum is the example of a jazz acoustic guitar. Here it becomes clear why this preamplifier has remained a staple in professional studios for four decades. We use a Warm Audio WA-14 (a clone of the AKG 414), positioned 50–60 cm from the instrument. Amplified through the ISA One, the signal remains exceptionally clean, detailed, and natural — a faithful representation of the instrument in an acoustic environment.
In the remaining examples, we examine the DI (Direct Input) section of the Focusrite ISA One. There is a distinctive functionality included only in this version of the modern ISA products, which effectively turns the ISA One into a dual-channel preamplifier. Watch the video to understand how this works, and you will also hear examples with drums, bass guitar, acoustic guitar with DI and microphone, and other interesting demonstrations in which we test the limits of this unique device.
