Audio Research REF750 SEL Monoblock Amplifier

Listening to Reference 750 SEL monoblocks in a high performance system is a transformative experience; under total control, speakers disappear from the listening room and the listener is transported into a three-dimensional realm where music takes on a palpable, tangible form. Details from source material are resolved against a black background, painting images in space with vivid reality. Bass becomes the foundation on which this living performance develops, produced with startling temporal and timbral accuracy. Here is the breath of the performer, the pick against the string, the brilliance of a full orchestra.

The Reference 750 SEL delivers over 750 watts of power into speaker loads of 4 to 16 ohms. This is achieved by the use of massive, custom-built power and output transformer delivering current from sixteen KT150 vacuum tubes in each channel. Thanks to 48 hours of burn-in, followed by thorough testing and careful matching of tubes, the amplifier requires little maintenance. Power supply regulation is also achieved by 6550WE and 6H30 vacuum tubes. Tube bias is controlled by two KT150 tubes, each driving a bank of eight KT150 output tubes.

The SEL is the last version of the 750-series, produced in a limited edition of ten pairs. Using the latest and best parts available, the SEL version includes 23 new wires and 26 new capacitors as part of a stunning sonic transformation. The best vacuum-tube amplifier in the world just got better.

• POWER OUTPUT: 750 watts per channel continuous from 20Hz to 20kHz. 1kHz total harmonic distortion typically 0.5% at 750 watts, below .04% at 1 watt. Approximate actual power available at “clipping” 850 watts (1kHz). (Note that actual power output is dependent upon both line voltage and “condition” i.e. if power line has high distortion, maximum power will be affected adversely, although from a listening standpoint this is not very critical.)
• POWER BANDWIDTH: (-3dB points) 15Hz to 150kHz.
• FREQUENCY RESPONSE: (-3dB points at 1 watt) 1 Hz to 200 kHz.
• INPUT SENSITIVITY: 4.6V RMS Balanced for rated output. (24 dB gain into 8 ohms.)
• INPUT IMPEDANCE: 200K ohms Balanced.
• OUTPUT TAPS: 4, 8, 16 ohms.
• OUTPUT REGULATION: Approximately 0.5dB 16 ohm load to open circuit (Damping factor approximately 17).
• OVERALL NEGATIVE FEEDBACK: 13dB.
• SLEW RATE: 20 volts/microsecond.
• RISE TIME: 1.5 microseconds.
• HUM & NOISE: Less than 0.2mV RMS – 110dB below rated output (IHF-A weighted, input shorted, 16 ohm output).
• POWER SUPPLY ENERGY STORAGE: Approximately 1300 joules.
• POWER REQUIREMENTS: 105-130VAC 60Hz (200-270VAC 50Hz) 2100 watts at rated output, 2400 watts maximum, 800 watts at “idle”.
• TUBES REQUIRED: (8) Matched pair KT150 Power Output; (1) 6550WE Regulator; (1) 6H30 Regulator Amplifier; (1) matched pair KT150 Driver; (1) 6H30 follower.
• DIMENSIONS: 13.5″ (34.3 cm) W x 23″ (58.4 cm) H x 20.8″ (52.8 cm) D. Handles extend 1.5″ (3.8 cm) forward and rearward.
• WEIGHT: 170 lbs. (77.2 kg) Net; 395 lbs. (180 kg) per pair shipped weight.