Περιγραφή
Unison Research SH – Class A Single-Ended Headphone Amplifier
The Unison Research SH is a Class A, single-ended headphone amplifier designed around a pure valve architecture with only two gain stages, both operating in triode mode, preceded by a passive volume control.
The circuit follows the traditional Unison Research philosophy of simple, high-quality designs that rely on intrinsic linearity rather than heavy feedback correction. The result is a coherent, natural sound reproduction with excellent tonal consistency across the entire frequency range.
The output stage uses EL84 pentodes operated in triode mode. This approach reduces operating stress on the tubes to around 20% of their maximum capability, significantly extending tube life while maintaining excellent sonic performance.
Despite minimal feedback (16 dB, excluding the output transformer), distortion remains typically below 0.15%, composed mainly of second harmonic with a smaller third harmonic component. This distortion remains stable across frequency and contributes to a natural and consistent tonal character.
The amplifier provides two parallel headphone outputs and includes a sensitivity selector to match different headphone types. High-sensitivity mode reduces output voltage by a factor of three, optimizing low-level listening and reducing noise floor.
Advanced power supply design with electronic stabilization and star-ground topology minimizes interference between stages, ensuring a very low noise floor and stable performance.
Technical Specifications
| Operating Class | Class A |
| Topology | Single-ended, 2-stage triode circuit with passive volume control |
| Input Stage | ECC83 / 12AX7 (Pure Class A) |
| Output Stage | EL84 in triode mode (Class A) |
| Inputs | 1 RCA line, 1 USB |
| Outputs | 2 parallel headphone outputs |
| Feedback | 16 dB |
| Output Impedance | 6.9 Ω |
| Damping Factor | 3 (on 20 Ω load) |
| Power Consumption | 45 W |
| Dimensions | 22.5 × 12.6 × 32.2 cm |
| Weight | 6 kg |
Performance
| High Sensitivity Mode (Output Voltage @ THD 1%) | |
| 150 Ω | 0.5 V |
| 33 Ω | 0.45 V |
| 10 Ω | 0.4 V |
| Low Sensitivity Mode (Output Voltage @ THD 1%) | |
| 150 Ω | 1.4 V |
| 33 Ω | 1.1 V |
| 10 Ω | 0.6 V |
Electrical Characteristics
| Frequency Response | 10 Hz – 50 kHz (-0.1 dB / -3 dB @ 50 kHz) |
| Input Impedance | 20 kΩ // 100 pF |
| THD | < 0.2% @ 1 kHz, 0.5 V / < 0.8% up to 1 V |
| Output Noise | ~18 µV (low sensitivity) / ~6 µV (high sensitivity) |
USB DAC (Internal)
| Type | Asynchronous USB 2.0 Audio Class |
| Resolution | Up to 32-bit |
| PCM Support | Up to 384 kHz |
| DSD Support | Up to DSD128 |
| DAC Chip | ESS Sabre (latest generation) |
| SNR | 110 dB (@ 1 kHz, A-weighted, 192 kHz) |
| THD+N | 0.008% (@ 1 kHz, -3 dBFS) |
| Isolation | Galvanic isolation between USB and conversion stages |
