Accuphase A-250 Class A Mono Power Amplifier
Ultra-massive pure Class A monophonic power amplifier Accuphase A-250 is built to excel in every respect. Carefully selected exquisite parts and materials are brought together to realise leading-edge technology. Enclosed by the refined champagne gold faceplate and a massive top plate cut from ultra-thick aluminum with a beautiful hairline finish, the amplifier exudes an atmosphere of solid elegance and dependable power.
Ultra-low-noise design with unprecedented S/N ratio of 127 dB brings out a stunning wealth of detail. Semiconductor MOS-FET switches enable output circuitry without any mechanical contacts. Two pure class A power units arranged right and left are driven in parallel to deliver 100 watts into 8 ohms with impeccable quality. A damping factor in excess of 1,000 means that speaker control is nothing less than perfect. The massive A-250 represents a new pinnacle in power amplifier history. Encounter music like never before.
- Pure Class A operation delivers 100 watts of quality power into 8 ohms
- Two totally identical power amplifier units driven in parallel
- 20-parallel push-pull arrangement of MOS-FET devices in output stage delivers linear high power progression to ultra-low 1-ohm impedance
- Input section configured as dual instrumentation amplifier
- Double MCS+ circuit and current feedback topology in amplification stage
- Support for bridged use of two A-250 units for even higher output power
- Strong power supply with massive high-efficiency toroidal transformer and large filtering capacitors
■ Fully balanced signal paths realized with dual instrumentation amplifier configuration
The A-250 features fully discrete circuit components in a dual configuration employing the latest instrumentation amplifier topology, allowing all signal paths throughout the power amplifier to be fully balanced. This not only eliminates any possible internal sources of noise or distortion as demonstrated by the outstanding performance ratings, it also makes the amplifier highly impervious to changes in ambient conditions. Consequently, operation stability and reliability which are crucial for a power amplifier have been dramatically enhanced.
■ Double MCS+ (Multiple Circuit Summing) in amplifier stage realizes highest-ever signal/noise ratio in an Accuphase component
The Double MCS+ configuration uses four circuits for amplifying the input signal, connected in parallel to keep distortion to a minimum and to further enhance S/N ratio and other parameters. The resulting level of sound quality is simply stunning.
■ Two totally identical power amplifier units driven in parallel
As shown in the circuit diagram of the amplifier section, the power amplification stage makes use of two completely identical power units, each with 10 N-chan- nel and 10 P-channel power MOS-FETs connected in parallel. These units are arranged on the left and right side of the chassis and driven in parallel, resulting in a 20-parallel configuration. This ensures a stable balance in terms of electrical operation, weight distribu- tion, thermal dissipation and other aspects. The parallel drive approach achieves a total allowable power dissipation value of 5.2 kW, which in turn reduces the power load on each MOS-FET, allowing each device to operate effectively in its range of optimum linearity
■ 20-parallel push-pull arrangement of power MOS-FETs delivers linear power progression: 800 watts (music signal) into 1 ohm, 400 watts into 2 ohms, 200 watts into 4 ohms, or 100 watts into 8 ohms.
■ Strong power supply with massive high-efficiency toroidal transformer and two large 100,000 µF filtering capacitors.
■ Printed circuit boards in power amplifier assembly made from glass cloth fluorocarbon resin with low dielectric constant and minimum loss.
■ 4-stage gain selector (MAX, –3 dB, –6 dB, –12 dB) also minimizes residual noise.
■ Two sets of oversize speaker terminals accept also spade lugs and banana plugs and allow bi-wiring connection.
■ Semiconductor (MOS-FET) switches used for protection circuitry prevent contact problems and ensure long-term reliability. Eliminating mechanical contacts from the signal path also further enhances sound quality.
■ Fully balanced input stage shuts out external noise interference.
■ OPERATION selector allows use of two A-250 units for bi-amping or bridged operation. Bridging allows upgrade to monophonic amplifier with even higher power, delivering 1,600 watts into 2 ohms (music signal), 800 watts into 4 ohms, or 400 watts into 8 ohms.
■ Output level indication switchable between 5-digit numeric readout and 40-point LED bar graph with further improved readability. Hold time selector button also provided. ● Meter operation on/off switch. ● Digital power meter showing true power values, based on output current detected by a Hall element. ● Power meter range selector and auto range function for automatic power tracking.
■ Major parts in power supply and signal path are gold-plated.