Proprius Monoblock Power Amplifier

Monoblock Power Amplifier

Clever-Simple-Reliable Value-For-Money Power

If you “applaud value for money products and clever simple designs that work reliably year after year” (see review by Ian Ringstead), these are the amps for you!

The Proprius monoblock power amplifiers will each deliver a continuous 25 rms Watts into 8 Ω and 45 rms Watts into 4 Ω at less than 1% THD, but will sound a whole lot louder.

They’re cute and compact but they’re not class-D! They’re linear class-AB for a superbly polished sound.

The Proprius is much more than an audio amplifier — it’s a most incredible sounding high fidelity amplifier you’ve simply got to hear!

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Specification Reviews

Clever – Arrange to Taste

With volume controls that go all the way, these power amps can be driven by a separate preamp (for example: the Majestic pre-DAC) by parking the volume at full — or their own volume controls can be used in a minimalst system driven by a fixed output source.

As a stereo pair the volume controls can be used to balance the stereo image if there’s no balance control anywhere else.

Bi-amping, tri-amping, and surround sound will benefit by using the Proprius volume controls, allowing you to easily adjust the tonal balance and/or audio image placement.

Monoblock Power Amplifier with Power Supply

A single Proprius monoblock power amplifier with its outboard power supply

Simple (and Smart) Design

Power amps don’t have to be brutish – they can be neat and compact as the Proprius shows – and at only 20.5 cm deep by 5.5 cm high by 10.5 cm wide, the Proprius is definitely neat and compact.

Proprius power amp side view

Cool running doesn’t always require dark, drab and dusty heat-sink fins – clean lines are possible as the Proprius heat-exchanger case shows. It doesn’t overheat even when used for long intervals at maximum output.

Easy to connect and get up and running, the Proprius can be used with “single-ended” and “balanced” sources using the same single input XLR socket (left). We’ve got a full range of interconnect cables making it simple to obtain the right one for your Proprius amps.

Proprius rear panelConnect power supply to the “48V” connector – both signal and power connectors are locking – and attach the speaker cable: the speaker terminals accept 4mm plugs; 8mm spades; or bare wire to 4mm diameter.

The Proprius amplifiers can be used free-standing wherever you want, or mounted on the back of speakers, making them into “powered monitors” using the supplied mounting kit.

Proprius speaker mounted

A Proprius monoblock amp attached to the rear of an Harbeth M20 monitor loudspeaker


The last thing we want is to be repairing the things we make – it’s so counter-productive. So that should give you a clue to why the Proprius has a number of features which make it reliable.

Proprius under the lid

Lid’s off the Proprius showing its truly linear class-AB circuit

We don’t want it to break when you forget yourself, and although we don’t advise on you being wreckless, we did lots of naughty things ourselves to test the reliability of the Proprius.

Knowing we were going to do this, we made the power devices as rugged as we could – yet we also needed them to be gentle-giants to resolve all the subtleties contained in your music.

Take a look at the giant output transistors bolted to the heat-exchanger chassis in the above shot. They’re rated at 200 Watts; 15 Amps and 260 volts! They can stand 40 times more power than Nyquist’s power amplifier theorem states is neccessary.

It means we don’t need to employ a protection circuit which is always meddling with your transient highs.

Instead, it’s intelligent remote power supply can detect when things are getting out of hand when it immediately shuts down and restarts when the problem goes away. But that’s not going to be during normal listening.

And then we added the final “failsafe” – a fuse (just in case).


Item Measurement
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

Specifications subject to alteration without notice in keeping with our continuous improvement policy.