Audio Research has upgraded its Reference Series to use the new KT150 output valve, so the Reference 250SE (250-watts per channel), Reference 150SE (150-watts per channel) and Reference 75SE (75-watts per channel) now all use KT150s in their output stages. But apparently the company didn’t just modify the output stages to accommodate the new valve; it also took the opportunity to incorporate other changes. ‘Not satisfied with merely changing output tubes, Audio Research decided to also include substantial performance upgrades in the Reference amplifiers to coincide with the changeover to the KT150,’ said Philip Sawyer, of Synergy Audio Visual which distributes Audio Research in Australia. ‘The resulting active and passive parts changes in the SE amplifiers have resulted in dramatic sonic improvements. Simply put, the new SE versions are better in every way: purity and lack of grain, resolution, micro- and macro-dynamics, separation and instrumental focus, phase and time coherence, and greatly improved bass weight, authority and control.

The good news for existing Audio Research owners is that their older Reference 75, 150, and 250 amplifiers can be fully upgraded to include all SE enhancements. For details and pricing on the new amplifiers, and the cost of upgrades to existing models, contact Synergy Audio Visual.

Manufacturer’s Specifications: Audio Research Reference 75 SE

Power Output: 75-watts per channel
THD: Typically 0.6% at 75 watts, below 0.05% at 1 watt.
Power Bandwidth: 7Hz to 60kHz (–3dB)
Frequency Response: 0.7Hz to 75 kHz (–3dB)
Input Sensitivity: 1.4V RMS BAL for rated output.
Input Impedance: 300kΩ Balanced
Output Taps: 8Ω, 4Ω
Overall Negative Feedback: 15dB
Slew Rate: 10 volts/microsecond
Rise Time: 4.0 microseconds
Hum & Noise: 112dB (IHF A-weighted)
Tubes Required:
2 × Matched pair KT150 – Power Output
2 × 6H30 Driver
Dimensions (WHD): 483×222×495mm)
Weight: 21.3 kg

Manufacturer’s Specifications: Audio Research Reference 150 SE

Power Output: 150 watts per channel
THD: Typically 0.6% at 150 watts, below 0.03% at 1 watt.
Power Bandwidth: 5Hz to 80kHz (–3dB)
Frequency Response: 0.5Hz to 120 kHz (–3dB)
Input Sensitivity: 2.0V RMS
Input Impedance: 300kΩ Balanced
Output Taps: 16Ω, 8Ω, 4Ω
Overall Negative Feedback: 14dB
Slew Rate: 13 volts/microsecond
Rise Time: 2.0 microseconds
Hum & Noise: –114dB (IHF-A weighted)
Tubes Required:
4 × Matched pair KT150
4 × 6H30 Driver
Dimensions (WHD): 483×222×495mm
Weight: 34.2kg

Manufacturer’s Specifications: Audio Research Reference 250 SE

Power Output: 250 watts per channel
THD: Typically 0.5% at 250 watts, below 0.04% at 1 watt.
Power Bandwidth: 5Hz to 70kHz (–3dB)
Frequency Response: 0.5Hz to 110 kHz (–3dB)
Input Sensitivity: 2.4V RMS Balanced
Input Impedance: 200kΩ Balanced
Output Taps: 16Ω, 8Ω, 4Ω
Overall Negative Feedback: 8.8dB
Slew Rate: 20 volts/microsecond
Rise Time: 1.5 microseconds
Hum & Noise: –110dB (IHF A-weighted)
Tubes required:
3 × Matched pair KT150 (Power output V1-6)
1 × Matched pair KT150 (Driver V7-8)
2 × 6H30 (Gain stage V9 and Regulator Driver V11)
1 × 6550C (Regulator V10)
Dimensions (WHD): 483×222×495mm
Weight: 21.3kg