Rega Osiris

Rega Osiris, the reference integrated amplifier

Rega made its name with turntables and affordable electronics renowned for their value for money. The Osiris runs counter to that image: it is the British manufacturer’s most ambitious integrated amplifier, the culmination of thirty-two years of transistor amplifier development. Two complete mono blocks housed in a single aluminium chassis, an oversized power supply and a signal path reduced to the bare essentials between the source and the speakers.

Two mono amplifiers under one cover

The Osiris is a dual-mono amplifier: each channel, left and right, has its own power supply and its own amplification stage, sharing nothing with the other. This separation eliminates interactions between the two channels and crosstalk, delivering a stable stereo image.

The signal path is based on a simple idea: reduce the number of stages it passes through. Where a conventional amplifier sends the signal through an active preamplifier before the power stage, the Osiris uses a passive volume control followed by a single amplification stage. Less electronics between the input and the speakers means less noise and coloration added along the way.

This choice has a trade-off. A passive volume control requires a source with sufficient output level to drive the power stage at full capacity; the Osiris compensates with high gain in this stage. Modern electronics, network players and converters generally provide a comfortable output voltage, which removes most of this limitation.

A dedicated power supply for each channel

The dual-mono design is first evident in the power supply. The Osiris incorporates two 400 VA toroidal transformers, one per channel, with high-quality cores. Each feeds a bank of 40,000 microfarads of in-house filtering capacitors, Rega’s K-Power series, for a total of 80,000 microfarads. This capacity forms the current reservoir from which the power stage draws during demanding passages.

The transformers are mounted to the chassis using a method that prevents their vibrations and noise from being transmitted to the enclosure, even when the mains supply is polluted. Rectification uses fast-recovery diodes, which generate less high-frequency switching noise and provide cleaner DC voltage.

The circuits that do not process the audio signal—input selection, display, microcontroller and overheat and short-circuit protection—have their own power supplies. The input stage and low-level circuits receive a regulated power supply with a low-noise voltage reference. The musical signal remains isolated from sources of interference.

Power reserves for demanding speakers

On paper, the Osiris delivers 162 watts per channel into 8 ohms and 250 watts into 4 ohms. The fact that power rises sharply when impedance is halved says more than the raw figure: it is the mark of a power supply capable of delivering current, not just voltage.

The output stage uses eight 200-watt Sanken transistors, four per channel, mounted in a high-current configuration. Upstream, a low-distortion, wide-bandwidth common-base driver stage provides the voltage swings required to drive any speaker load. The cascoded differential input stage relies on two LED-referenced current generators, while the amount of feedback is designed for tight bass control.

The attention to detail extends to component selection: Nichicon audio capacitors for decoupling, electrolytic capacitors supplemented by polyester models to refine the upper frequencies, and low-inductance power resistors in the output stage. In practical terms, the Osiris remains in control of low-sensitivity or low-impedance speakers without showing any signs of strain.

A chassis machined from aluminium

The Osiris enclosure is machined from solid aluminium panels. The left and right sides incorporate heat sinks running from front to back, designed to dissipate heat from the transistors. The chassis is rigid and low-resonance, isolating the electronics from external vibrations and providing a stable thermal environment.

This construction comes with a weight: 25.6 kg for 434 mm wide, 122 mm high and 350 mm deep. It is best to reserve a sturdy piece of furniture or rack for it rather than a simple shelf. Rega supplies a fully shielded reference mains cable of its own manufacture and a machined remote control for volume and input selection.

Analogue inputs and a direct input

In terms of connections, the Osiris remains analogue from end to end. It offers four RCA line inputs and one balanced XLR input, plus a recording loop with dedicated input and output. Two pairs of gold-plated terminals accommodate speaker cables and allow bi-wiring of a single pair.

The direct input deserves a mention. It bypasses the volume control and feeds the power stage directly at fixed gain. This allows the Osiris to be integrated into a home theatre system: the audio-video processor manages the level of the front channels, while the Osiris amplifies them at the same volume as the rest of the system. The same input can also be used to drive the unit from an external preamplifier.

Remaining fully analogue means planning for the appropriate components. A digital source, network player or turntable with a digital output requires a converter connected to a line input. A turntable requires a separate phono preamplifier, as the Osiris does not have one. This approach keeps the signal path short and clear, leaving the listener to choose these components.

Frequently asked questions

“Passive preamplification”: do I need to add a preamplifier?

No. The Osiris is a complete integrated amplifier, ready to accept your sources and drive your speakers. The term “passive” describes its internal structure: volume adjustment is performed without an active preamplifier stage. An external preamplifier only comes into play if you use the direct input, which bypasses the unit’s volume control.

How do I connect a turntable to the Osiris?

By placing a phono preamplifier between the turntable and a line input on the Osiris. This unit boosts the very low signal delivered by the cartridge and applies RIAA equalisation. The choice of model depends on the type of cartridge fitted to the turntable, moving magnet or moving coil.

Can the Osiris play digital sources such as a network player?

Yes, provided you use a digital-to-analogue converter. The Osiris has neither a digital input nor a built-in converter. A network player or streamer with an analogue output connects directly to a line input; otherwise, an external converter provides the link.

Does the balanced XLR input make any difference to the sound?

It is most useful with a genuinely balanced source and over long cable runs: a balanced connection rejects interference picked up by the cable. With a conventional unbalanced source connected via RCA, the XLR input offers no particular advantage. The benefit therefore depends on the rest of the system.

Where should a 25.6 kg unit that gets hot be installed?

On a stable, level support capable of handling the weight, with open air around the enclosure. The side heat sinks need clearance to dissipate heat: it is best to avoid confining the Osiris in closed furniture or placing another unit on top of it.

Can the Osiris be integrated into a home theatre system?

Yes, thanks to the direct input. It allows the home theatre processor to manage the volume of the front channels, while the Osiris provides their amplification. The same pair of speakers can then be used for music, via the line inputs and volume control, and for films, via the direct input.

Technical Specifications

Audio Performance

• Output Power:
  • 162 W at 8 Ω
  • 250 W at 4 Ω
• Sensitivity:
  • Input 1: 250 mV, impedance 10 kΩ (balanced)
  • Inputs 2-5 and recording: 220 mV, impedance 22 kΩ
  • Direct input: 220 mV, impedance 50 kΩ
• Gain: Direct input: 44 dB
• Frequency response: 10 Hz (point at -1.7 dB)
• Total harmonic distortion and noise: < 0.05% (bandwidth 22 Hz to 30 kHz)

Connectivity

• 1 balanced XLR input
• 4 RCA line inputs
• 1 recording input/output
• 1 direct input

Physical Characteristics

• Type: Dual mono amplifier
• Dimensions (W × H × D): 434 × 122 × 350 mm
• Weight: 25.6 kg

Other Specifications

• Remote control: Philips RC5
• Mains fuse for 230 V version: 3.15 A
• Supplied with a high-quality, fully shielded power cord designed by Rega