Focusrite grew out of a 1985 request from Beatles producer George Martin to recording console designer Rupert Neve (after he'd sold his eponymous company), to build a no-compromise mic pre and EQ for the Forte mixer — destined for Air Studios on the island of Montserrat — and subsequently ravaged by a volcano! The modules, prefixed with the letters ISA (Input Signal Amplifier), featured a mic preamplifier with the Lundahl LL1538 transformer, used in every Focusrite ISA mic pre since. Why did Rupert Neve choose Lundahl, rather than a Marinair transformer as used in the Neve 1073 module, and what makes this transformer from the northern part of the Stockholm archipelago so special?

To understand why, we need to transport ourselves back to the '80s. Nowadays, transformers are touted by some manufacturers as talismanic 'vibe bringers'. However, in 1985 audio signals passed not only through mic input transformers, but were conveyed to console outputs, into tape recorders, out of tape recorders and back into mixers again via transformers at each stage. While the gain and electrical isolation provided by this circuitry was mainly necessary, the 'funky' harmonic spectrum imparted by this group of galvanics was not always appreciated by production pros. Back in the day, engineers and producers were, in fact, looking for a cleaner and more 'transparent' sound. Neve turned to the LL1538 because of its open and expansive character imparted when amplifying mic signals. To understand why, it's worth considering how transformers are made, and understanding how the Norrtälje-based Lundahl factory makes devices with a difference.

If you've seen a modern electronics production line, then a visit to a transformer manufacturer can be a bit of an eye-opener, with distinctly mid 20th-century equipment, a lot of manual work and a decidedly home-spun atmosphere. The spinning metaphor is apt, as there are plenty of bobbins and wire, and a very low-precision environment when compared to PCB production. This is where the Lundahl operation differs: apart from the raw wire and mumetal, everything is custom-made onsite.

The Lundahl transformer configuration was developed from first principles by founder Lars Lundahl, who re-imagined the way a transformer was constructed from magnetic core and coils of wire. It's a family business: son Per took over as MD in 1994. Not only did Lars Lundahl develop his own way of making a transformer, but he also designed all of the manufacturing equipment! A full-time machinist remains part of the Lundahl team, to assemble new equipment and maintain existing machines.

Lundahl transformers use 'stick wound' coils: the wire is wound in layers on a coil PET former. The use of stick winding with interlayer insulation provides a coil that is uniform in geometry from end-to-end and layer-to-layer, resulting in better (and more consistent unit-to-unit) electrical performance than the more common bobbin winding process.

The winding operation is overseen by skilled workers, but the winding itself is computer-controlled with design-specific software. Every coil is the same as every other and performance matching between transformers with the same part number is excellent. This is one of the key reasons Focusrite have used the same Lundahl component for every device in the ISA range over 30 years: the assurance that the user will receive great sound exactly as it was designed.

The flat winding process has several benefits, one of which is that Lundahl can include a Faraday shield which extends beyond the edge of the windings, to better block electromagnetic interference. Lundahl have a stellar reputation in the audiophile world, where signal levels can be far lower in level and more vulnerable than those from professional microphones. When Rupert Neve chose the LL1538 he was making a conscious 'step up' from the type of artisanal construction used for transformers in the vacuum tube/valve era.

Want to hear the Lundahl LL1538 in action? Check out our ISA range here.

Words: Nigel Jopson

Photos: Lundahl Transformers