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Graham Slee Proprius Mono Block Power Amplifier Pair

Graham Slee Proprius Mono Block Power Amplifier Pair
Graham Slee Proprius Mono Block Power Amplifier PairGraham Slee Proprius Mono Block Power Amplifier PairGraham Slee Proprius Mono Block Power Amplifier PairGraham Slee Proprius Mono Block Power Amplifier PairGraham Slee Proprius Mono Block Power Amplifier PairGraham Slee Proprius Mono Block Power Amplifier Pair
(£1,082.50 Exc. VAT)

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01892 532 995

  • All the sonic hallmarks you expect from Graham Slee
  • Compact Proportions
  • Volume control for more flexibility
  • Balanced or Single-Ended Input In One
  • Intelligent output protection
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Why buy from us?

Proprius Mono Block Power Amplifier Pair

Seven Great Reasons to Choose the Proprius

1. The Sound

The Proprius has all the sonic hallmarks you expect from a Graham Slee design.

Listening is riveting, involving and fatigue-free. Using two for stereo, imaging is spatially focused and "walk-through" - transcending the speakers, but importantly, the music remains cohesive. The Proprius is tonally accurate producing a silky and fluid treble with no hint of brightness or grain. Good bass extension and articulation meters out appropriately scaled slam and "grunt", as well as rhythmic satisfaction.

Vibrant dynamics with impeccable timing keep a grip on the performance, with no loss of underlying subtle melodies.

2. Generously Rated

You may think a 25 watt amplifier is too frail, but the Proprius is anything but! Each output transistor can handle 25 amp peaks and 200 watts, and at 30MHz their high frequency performance is ten times higher than regular output transistors.

The Proprius outboard power supply is 120 watts to provide unassisted the 2.5 amps its 20 volt peaks demand. Only with impedance dips and when driving 4 Ohms are its reservoir capacitors called on to release stored energy required to ride transient peaks.

3. Compact Proportions

Finding space for all your hi-fi gear can be tricky, but at just 10.5cm (4.1") x 6cm (2.4") x 20cm (7.9") you'll easily find the space for a pair!

4. A Power Amp With A Volume Control?

Why not? We gave the Proprius a volume control to give you more  flexibility. In a frugal single source system you don't need a line-stage, just a pair of Proprius. In a surround system you might wish to balance the sound levels on each amp. The same if you're bi-amping or tri-amping.

What if your preamp doesn't have a balance control? But if you don't need a volume control, just set it to max!

5. Balanced or Single-Ended Input In One

A single XLR input connector accepts both balanced and single ended feeds. Connect it to a balanced source and the interconnect length can be considerably longer meaning you can place the Proprius at the speaker, or even screw it to the speaker back with the supplied adaptor plates.

6. High Bias

Most domestic listening is done at around 1 watt. With medium sensitivity speakers that single watt produces around 80-90dB of sound pressure one metre in front of the speakers. The emotional signature and spatial information in the music is much lower in level - perhaps a tenth of a watt or less.

Unless properly biased into conduction, an amplifier output stage will distort and sound "dry" (Class-B). Give it more bias and the sound is clearer with more body, but give it too much bias (Class-A) and the bandwidth is curtailed often resulting in a "warm" and "syrupy" sound.

High-Bias provides just the right amount, bringing out the emotional signature and spatial information your music craves.

7. Hot Pluggable

Untypically the Proprius behaves impeccably during power-up and power-down - no loud "thuds" so it doesn't have or need any current stealing output relays. There are no damaging DC offsets so you can plug and unplug its XLR without fear.  It has intelligent output protection (which incidentally doesn't act prematurely) and because it doesn't have any nasty DC offsets on its output, it allows you to connect and disconnect speakers while it's on. And because there is no DC on its output it cannot damage your speaker voice coils.

Shipping typically 1-3 days
  • 25 Watts into 8 Ohms / 45 Watts into 4 Ohms
  • High biased discrete transistor power amp – not class D or T
  • Rugged 25 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 control can be "parked" at full when controlled from a preamp
  • Effective heat radiator case for comfortable high-bias running
  • Individual 120 Watt remote switchmode power supply with each Proprius
  • 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

UK Delivery

  • FREE delivery via DPD Local By 12pm on orders to value over £300, including one hour delivery window service 'Predict & Follow My Parcel'.
  • Royal Mail Special Delivery By 1pm costs between £5.00 - £10.00 on orders to value under £300, dependent on weight.
  • Saturday or Sunday delivery available upon request for supplemental charge.

EU Delivery

  • £25 delivery charge 'Flat Fee' via DHL Europe by Road service (5-7 days) which provides comprehensive tracking of shipments online.
  • £50 delivery charge 'Flat Fee' via DHL Europe by Air service  (2-3 days) which provides comprehensive tracking of shipments online.
    Receiver is responsible for the payment of local Duties and Taxes.

USA & Canada Delivery

  • Services based on your order being shipped to the U.S. and Canada are calculated as follows:
    £100 delivery charge 'Flat Fee' via DHL international 'Day Definite' service per parcel.
    Receiver is responsible for the payment of local Duties and Taxes.


  • Not all products are available for order into Europe, USA & Canada


  • Full manufacturer's warranty on all new purchases. Standard warranty is typically 12 months to 2 years with some goods coming with 6 years manufacturer's warranty.
  • Goods purchased in UK and EU are covered by the Consumer Contracts Regulations.
Average Rating (1 Review):  
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Perfect for us.
01 October 2022  | 

They do exactly what we wanted. The combination with our Spendor A2s sound fabulous in our little room.

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