Custom LA-2A Design Opto Stereo Compressor (IGS T4BX / Lundahl / Carnhill)

Custom-built stereo LA-2A-style optical compressor, built in Finland in 2017 by a local audio engineer. The unit features a custom-designed PCB and high-quality components, including IGS Audio T4BX opto cells, Carnhill and Lundahl LL1922 transformers, as pictured.

The unit is fully functional and sounds as intended. It has some rack rash, as shown in the photos, and the switches and knobs could use some tightening. These are cosmetic/mechanical issues and do not affect the audio performance.

In addition to the standard compression controls, the unit featured a stereo link feature and a Drive control designed to introduce additional harmonic saturation, emphasizing 2nd- and 3rd-order harmonics for a different tonal character per channel.

The DC detection / sidechain circuit is solid-state rather than tube-based. This was a deliberate design choice: the original LA-2A uses additional tube circuitry for deriving the control signal, whereas a solid-state detection circuit provides the same basic function without running additional tubes solely for DC/control-voltage generation.

A serious DIY/custom build with high-quality transformers and opto cells. A great option for anyone looking for LA-2A-style optical compression with some additional flexibility in the harmonic character.