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LPU I Phono Pre-Amplifier

SW1X Audio Design™ LPU I

Performance Level 1
MM Valve Phono Pre-Amplifier


The phono pre-amplifier is based on a classic all valve circuit design used to master vinyl recordings and master tapes.

It is a two gain stage design consisting of 2 (one for each channel) pentode valves on the input and one double triode valve on the output.

The input stage utilises lush sounding EF86 valves in pentode mode, which are loaded by active RIAA equalization network (series resistor-less, dynamics preserving), driving the powerful 6N6P or 5687 double triode on the output stage.

LPU I, LPU II and LPU III family of Phono Pre-Amplifiers share similar tube input stage- a pair of EF86 pentode tubes. Due to the brilliant sound character of the EF86 those tubes were commonly used in many radios and RTR tape recorders in the early 60s. The idea of their circuit design was borrowed from the input stage of early Reel to Reel (RTR) tape recorders, which were used in the mastering studios and radio stations. Maybe that is one of the reasons as why most recording from the 60s are sounding at their best, much better than from the 70s and 80s? In a way, the EF86 input tube design closes the loop and makes all our LPU Phono Amps range a time-less classic.

SW1X Audio Design™ LPU I Features:

  • Specially Selected and Harmonically Matched Component & Material Quality
  • MM Phono Pre-amplifier is suitable for all moving magnet (MM)  or moving coil (MC) in combination with a matching SUT
  • Classic 2 Gain Stage Pentode Input-RIAA-Triode Output Design
  • Based on 2 x EF86 Pentode Valves on the Input and 6N6P/5687 Double Triode on the Output
  • Pure Class A, Zero NFB, Single Ended, all Valve Amplification RC (resistive loading/capacitive de-coupling) Circuit Topology
  • Active Series-Resistor-less RIAA Equalization for maximum dynamics
  • SW1X Brass body Al Film de-coupling Capacitors in Inter- and Output Stage
  • 6X5 or 5Y3 Valve Rectified CLC2RC (choke filtered) B+ Power Supply
  • 47K Input Impedance & <1K Ohm Output Impedance
  • Total Gain is approx. 40-46 dB depending on the Choice of Valves
  • Maximum Input Voltage: 350mV
  • HQ, EI Core, 110/115/230/240V AC mains transformer

Tube Compliment:  2 x EF86, 1 x 6N6P / 5687 or ECC88/6DJ8, 1 x 6X5 or 5Y3

M. Fremer’s Review of SW1X LPU I RIAA MM Phono is out on Stereophile



Note: Due to SW1X Audio Design’s ongoing research and development process, specifications are subject to change without notice.


Dimensions: Height (mm) 140 x Width (mm) 340 x Depth (mm) 410

Weight (kg): 10

Max Power Consumption (W): 32

Output Noise, Unweighted (mVrms): < 0.5

Output Impedance (k Ohms): <1

Tube Compliment:  2 x EF86, 1 x 6N6P or 5687, 1 x 6X5 or 5Y3

Front panel options: brushed Silver or matte Black

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