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Graham Slee Proprius Monoblok Power Amplifier


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Ex VAT: 540.83

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Power Per Channel (8ohms) 25W
Warranty length 2 Years
Brand Graham Slee

Tech Specs

Power output (rms) measured: 26 Watts into 8 Ohms; 45.5 Watts into 4 Ohms (ref 1% THD+N at 1kHz)
Power bandwidth at rated power into 8 Ohms: 10Hz - 47kHz (-3dB), 20Hz - 25kHz (-1dB)
Power bandwidth at rated power into 4 Ohms: 12Hz - 40kHz (-3dB)
Total harmonic distortion and noise at 8 Ohms: 100Hz: 0.043%; 1kHz: 0.047%; 5kHz: 0.061%; 10kHz: 0.085%; 20kHz: 0.125%
Total harmonic distortion and noise at 4 Ohms: 100Hz: 0.066%; 1kHz: 0.071%; 5kHz: 0.094%; 10kHz: 0.129%; 20kHz: 0.181%
Signal to noise ratio in dB: "A-weighted": 87dB; 22Hz-22kHz "Q-pk": 80dB
Bias type: Class Ab; Bias current: 60mA (approx.)
Input sensitivity for rated output: 575mV rms
Short circuit protection: Fuse and power supply shut-down (short circuits should be avoided to prevent component stresses)
Fuse: F2A 5mm x 20mm (glass "quick-blow" fuse rated at 2A)
Power supply: 48V DC, 120 Watt - self adjusting to AC mains 100V - 240V, 47 - 63 Hz; IEC cord supplied
Size (approx.): Amp W105 x H55 x D205 mm; Power supply W65 H40 D170 mm

Product Description

Graham Slee Proprius Power Amplifier Monoblok is a mighty miniature that delivers a powerful 25W into 8 Ohms (RMS) and 45W into 4 Ohms and sounds stunning. Graham Slee decided to design Proprius as a mono power amp for a variety of reasons - one of which allows them to be used either remotely (on your hi-fi rack) or right next to each speaker for powered monitor performance. The great thing about monobloks is they also give you true dual-mono amplification for improved stereo separation. Simply order 2 for a stereo set-up.

They're perfect for use with high sensitivity speakers where quality comes before quantity. However, they're not short on quantity and sound louder than their 25 watt rating would suggest, even using speakers as low as 83dB sensitivity - including the Stirling Broadcast/BBC 11 Ohm LS3/5A.
Proprius Mono-Block Power Amp Rear Panel Proprius Mono-Block Power Amp

The balanced XLR input works just as well single ended with shorter interconnects so using them side by side like a normal amp isn't a problem. For remote or speaker mounted placement requiring long cable runs, you'll need a source with balanced outs and our balanced audio cables.

Unusually for a power amp, the Proprius is equiped with its own volume control meaning it can be used direct from a fixed output source. When using it with a control preamp the volume control is put "out of circuit" by parking it at full rotation. The input is based on the balanced topology by David Birt of the BBC, modified to "all-inverting" making it free of common mode distortion. Absolute phase is accomplished by "phase swapping".

A welcome addition to the Graham Slee range of reference quality headphone amplifiers and phono stages, order online or contact us to arrange to try Proprius in our showroom or on a home trial in your system.

Speaker Mount

This mounting bracket (included with every Proprius) allows you to attach Proprius to your speakers for an exceptionally short run of cables to speaker (almost no cables, shown here mounted to the rear of Harbeth M20 speakers! Be careful not to damage speaker crossovers when drilling into speakers). Otherwise, you can simply have Proprius next to your speakers on the floor. 


- 25 Watts into 8 Ohms / 45 Watts into 4 Ohms
- Class AB biased discrete transistor power amp – not class D or T!
- Rugged 15 Amp 30MHz output transistors
- No DC offset on output – safe to leave speakers connected
- Balanced or single-ended line level input
- Full range of cables and adapters available — stock designs or bespoke
- High-end professional gold plated XLRs on input and power
- Can be used free standing — or remotely on loudspeakers (brackets supplied)
- Individual volume controls can be "parked" at full when controlled from a preamp
- Effective heat radiator case for cool class AB running
- Individual 120 Watt remote switchmode power supply with each Proprius

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