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SW1X Audio Design™ SPA IV Apollo

Performance Level 3/4/5
2A3 DHT Power Amplifier

SPA IV is a 3 gain stage Stereo Power Amplifier without input switch and volume control. Therefore it is ideally paired with our PRE III or PRE IV Line Pre-amplifier.

Available in different versions: Standard, Special and the limited Classic or Signature versions with different power output transformer options (M6, SHiB and UHiB) and all Copper or Copper/Silver  windings

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SW1X Audio Design™ SPA IV Integrated Amplifier Features:

  • Specially Selected and Harmonically Matched Component & Material Quality
  • Single Ended, absolutely Zero NFB, Class A, Directly Heated Triode Valve Power Amplifier
  • 2 x 6J5/6SN7 Triode driver/input Stage Valves driving the 2 x 2A3 DHT Valves
  • 3 Amplification Gain Stage Design
  • Point 2 Point Hardwiring Technique for the most consistent production results
  • Internally wired exclusively with our SW1X Magnum, Genesis and Opus conductors
  • SW1X Audio DesignCustom Designed (50 Watt) Signal Output Transformers
  • Quasi Mono, Directly Heated Double Diode Valve Rectified B+ Power Supply
  • Orient grain M6 EI core mains Transformers & Chokes
  • Valve rectified Fixed Bias Power Supply


Tube Compliment:  2 x 6J5, 2 x 6SN7, 2 x 2A3, 1 x 5U4GB, 1 x 5Y3


SPA IV is avaiable in 4 Versions with either Satin Silver or Matte Black front Panels

with a following output transformer (OPTs) specifications:

  • Standard : SW1X Audio Design all Copper wound, orient grain M6 EI Core OPTs
  • Special :  SW1X Audio Designall Copper wound Super HiB DC Core OPTs
  • Classic : SW1X Audio DesignCopper/Silver Windings, Super HiB DC Core OPTs
  • Signature : SW1X Audio Design™ Silver/Silver Windings, Super HiB DC Core OPTs


SW1X Audio Transformers


Optional Extras

  • Silver wound SW1X Audio DesignCustom Designed Super HiB or Ultra HiB DC core Signal Output Transformers
  • Fully Hardwired Tube Output Stage on the Bakelite Board
  • Fine Silver wiring on the Input, Bakelite Board and Output
  • AN 2W non-magnetic Niobium resistors on a Hardwired Bakelite Board
  • Super HiB double C-Core mains transformers
  • Inter-stage signal decoupling capacitors: 1. Copper Foil in Oil or 2. Silver Foil capacitors
  • AN 2W silver, non-magnetic, Tantalum resistors





Single Ended, Class A, Zero NFB, Output Power (W): 4, which sound at least like 25 Watts and the dynamic delivery feel like 250 W

when paired with with High Sensitivity Speakers (min 96dB/W/1m is recommended)

Input Sensitivity (V): 1

Input Impedance (Ohms): 47K or 100K

Output Impedance (Ohms): 4 & 8

Max Power Consumption (W): 250

Output Noise, Unweighted (mVrms): < 0.5

Dimensions (without tubes and feet): Height (mm) 250 x Width (mm) 440 x Depth (mm) 400

Weight (kg): 35


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

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