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  Direct Servo Subwoofer Amplifiers
Our range of dedicated subwoofer plate amplifiers


These amplifiers are showcases of our pursuit of perfection for those who seek more than just basic functions.

Features include:

  1. Harmonic distortion is less 0.01% at 200WRMS @4ohms (-3 dB from full output). This amp can surely qualify as an ultra low distortion amp.
  2. All OP amps on the signal paths are OPA2134 and TL072 for better sound quality (SQ) and richer bass sound.
  3. MOSFET transistors for power amp's input stage for a more smooth sound.
  4. Class A/B operation for A series amplifiers and class-H operation for H series amplifiers. These are pure analog amplifiers (no digital sound). We use bigger transformer, bigger filter caps, and bigger one piece 3/16" thick back plate/heat sink construction for better heat transfer and rigid structure. Power rating is tested for 4 continuous minutes.
  5. A defeatable extension filter with separate frequency and damping control. The extension filter can be bypass with 14 Hz and high damping setting. Frequency is adjustable between 14, 20 and 28 Hz. Damping factor is adjustable between high damping (Q=0.6, or bessel filter), medium damping (Q=1.07, or 1.5 dB boost Chebyshev), low damping (Q=1.33, or 3 dB boost Chebyshev). There are a total of 9 settings available. You can use this filter to boost the bottom end or do minor correction for room response. In case you don't know, our competitor has a 6 dB boost at 30 Hz which cannot be defeated. To defeat that, you have to unmount the circuit board and do some soldering, voiding the warranty if there is one. Incorrect rumble filter not only makes the bass sound boomy, it can even bottom out the woofer.
  6. Damping factor: 160 @ 4ohms. (Note: damping factor is speaker wires dominated. Without speaker wires, the native damping factor is >800).
  7. Signal to noise ratio: better than 107 dB (A-weighted).
  8. Input impedance: 30k ohms.
  9. Air tight by designed. No need for a back cover or separate chamber. It will give you an extra 0.15 cu ft enclosure net volume compared with those with back covers.
  10. Auto ON/OFF on left channel input.
  11. Accept both high level (from speaker) and low level (from preamp or processor) inputs.
  12. Fixed high pass line level output for satellite speakers.
  13. Continuous phase adjustment (0-180) and low pass filter adjustment (25-120 Hz).
  14. Gold plated connectors.
  15. Build-in thermal and short circuit protection circuitry.
  16. The phase control is vastly improved so that it has better control in the non-HT setup.
  17. Subwoofer crossover adjustable range is increased to 25-120 Hz for more flexibility.
  18. HP filters for satellite is modified to -3 dB@100 Hz with Q=0.6.

This amp also carries a 2yr warranty against defects (does not cover abuse or installation errors). All other features such as protection circuits are same as regular amps.

  • Dimension: (W)10-3/8"x(H)12-7/16"x(D)4".
  • Cutout Dimension: (W) 9 1/8" x (H) 11 1/8".
  • Big power transformer with 650W max input power. Net weight is 15-18 lb.

Quality components

The op amps used here are audiophile grade OPA2134 and TL072. OPA2134's are used in the high pass section (the one for front speakers filtering). On the subwoofer signal path, the op amps are mixtures of OPA2134 and TL072. The reason for us to use TL072 is for its richer bass sound. At half of full output rating, the distortion is less than 0.01%. In addition, similar to the A370 servo amps, there is no electrolytic capacitors on the signal and feedback paths.