LJ 2x25W Class-A JFET-MOSFET Single-ended Amplifier (Pass Aleph J)

Merek: LJ Audio, Indonesia
Kode Produk: Aleph J #1
Ketersediaan: Tersedia
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This is 2x 25W JFET-MOSFET class-A single-ended custom amplifier by LJ Audio, with dual input (XLR true balanced or RCA single-ended).  Custom made only, approx lead time: 3 weeks.

  • Model: Aleph J clone Ver #1, Jan 2014 (protoyype).
  • Design:
    • Adapted from FirstWatt Aleph J by Nelson Pass. The original Aleph J is based on the circuit design of the Aleph series. It is a two stage concept with a p-channel. JFET differential amplifier with a current source at the input and a single ended class A output based on the active current source concept with two identical output stages in parallel.
    • Aleph J circuit (There are differences between the Aleph J and its predecessors.):
      • Improved power supply filtration with about 20dB less voltage ripple.
      • Reduced gain on the active current source, giving better overall performance into 8-16 ohm loads.
      • Input stage using high quality matched JFETs.
      • Much higher input impedance and vanishing capacitance.
      • 15dB less negative feedback.
      • Even greater stability, operating without lag compensation.
      • 15dB less noise.
      • No electrolytic capacitor in the signal path.
    • Circuittry and technical stuff at www.firstwatt.com
  • Original specification (based on the published technical data of original Firstwatt Aleph J, measured at 8Ω load):
    • Input Impedance: 242 kΩ (RCA input).
    • Damping Factor: 20.
    • Output Power: 25W with 1% THD at 1kHz, 30W clipping.
    • Gain: 19.6dB.
    • Input for 25W output: 1.5V.
    • Maximum output voltage: ±21V.
    • Maximum output current: ±2.5A.
    • Noise: 100μV unweighted, 20Hz-20kHz..
    • Power consumption: 200 watts.
    • Fuse: 3AG slow blow or 4 A (120VAC), 3AG slow blow or 2 A (240 VAC).
  • Features:
    • Dual input: XLR true balanced and RCA single-ended.
    • Loudspeaker protector module with triple protection TFX PGX-600S.
    • Soft start module (anti inrush current) TFX ASX-2200.
    • Triple fan (inflatable fan, and suction fan) controlled by thermal sensor.
    • Separated (independent) PSU each channel (dual transformer, dual rectification and filtering).
    • "Killer" capacitance filter: 312.000uF.
    • Full body aluminium heatsink.
  • Key Parts/Components:
    • Very low noise J-FET: 2SJ74.
    • Power MOSFET: IRFP240 (HEXFET, vertical).
    • Rectifier: 16x MUR1560 with heatsink (downgradeable option).
    • Resistor: TKD (Japan), Takman (Japan), Dale (USA).
    • Capacitors (upgradeable option): Vishay Roedersein, Elna, Panasonic, Bennic FPP.
    • Transformer: LJ custom trafo.
    • Heatsink: Aluminium full body.
    • Connector: Neutrik XLR, gold plated Vermouth RCA and binding post. 
  • Chassis: custom aluminium chassis with 10mm acrylic panel.
  • Construction: PCB (fibre glass, dual layer thru hole, gold plated).
  • The parts and components are subject to change.

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