SW1X LPU 1 SPX

The SW1X LPU I SPX is a Moving Magnet valve phono preamplifier built on a circuit topology borrowed directly from the input stages of the reel-to-reel tape recorders used in mastering studios and radio stations of the 1960s, a two-stage design using EF86 pentode input valves that were themselves found in the finest recording equipment of that era, loaded by an active series-resistor-less RIAA equalization network and driven by a 6N6P or 5687 double triode on the output.

Type and Technology

Moving Magnet (MM) valve phono preamplifier, two-stage design. EF86 pentode input stage with active RIAA equalization, series-resistor-less, dynamics-preserving design. 6N6P or 5687 double triode output stage. Pure Class A, zero negative feedback, single-ended all-valve amplification. RC topology with resistive loading and capacitive decoupling. Valve-rectified CLC choke-filtered B+ power supply (6X5 or 5Y3 rectifier). PIO or film/foil decoupling capacitors. 47k ohm input impedance. Compatible with any MM cartridge, or MC via a matching step-up transformer. Total gain approximately 40–46 dB depending on valve choice. Available in brushed Silver or matte Black.

Sound Character

Musical, organic, and tonally alive in the tradition of the best all-valve phono stages. The EF86 input tube has a particular lushness and openness that solid-state phono stages cannot reproduce, a quality that made it the preferred input device for broadcast and mastering equipment at the height of the golden age of vinyl recording. The active series-resistor-less RIAA equalization preserves the dynamics of the source material more faithfully than passive designs. The result is a phono stage that presents vinyl as it was meant to sound.

Build and Finish

Hand-assembled to SW1X Audio Design's specifications with specially selected and harmonically matched components. HQ EI core mains transformer supporting 110/115/230/240V AC. Optional upgrades available including AN copper foil in oil signal output decoupling capacitors, AN 2W copper non-magnetic tantalum film resistors, premium vintage NOS output tubes, and orient grain M6 EI core copper flux-banded mains transformer.

Best For

Analog purists who want a valve phono stage with a direct lineage to the mastering equipment of the 1960s and the tonal character that the EF86 tube uniquely provides, for Moving Magnet cartridges, or MC via a suitable step-up transformer.

Specifications