Graham's Blog Archive

Summarising The Proprius

Posted by Graham
November 11th, 2012

If you’ve been following my Proprius mono-block power amplifier news you’ll remember I said I’d summarise its features, but there are several.

What I want to do is pick just four – the four best features which combine to make the Proprius mono-block power amplifiers truly unique. In my opinion they are . . .

Power Output

25 watts done properly can sound much louder than 25 watts done badly. Solid state amps generally don’t “hold a note” well. They lose out above lower bass frequencies because above that open-loop gain falls away rapidly (it halves every octave).

They use negative feedback to flatten their frequency response – but it’s not true negative feedback because the output is falling with frequency whilst the input is flat.

A musical note isn’t a single frequency. It’s a combination of frequencies, so there’s a number of negative feedback levels the amp is trying to deal with at the same time and they’re all at different levels on a falling scale.

The result is what’s termed as “all leading edge”. They can hold the leading edge at full power – the start of a note, but can’t keep all the note at the same amplitude it was intended to be.

Measurements are made using sine waves – no one is lying – they’re telling the truth, but music is a complex mixture of a great number of sine waves – a musical note being shaped by many, and power measurements can’t determine the true power from that – how loud it will be.

The Proprius open loop frequency response is far wider. It doesn’t fall away so soon – in fact it’s nearer the upper end of the audio spectrum before that starts to happen. It can therefore form the notes more accurately giving a full sound – and therefore it sounds louder than you’d think. You don’t have to turn it up loud to hear the music!

So, is it a valve amp? No, it’s a solid state amplifier done the right way – it’s valves done by transistors.


The Proprius speaker terminals allow you to plug 4mm banana plugs straight as well as at right angles allowing you to use two sets of speaker cables for bi-wiring.

Speaker Mounting (or using it remote at the speakers)

Simply by removing the screw-on feet and attaching the speaker mounting kit, the Proprius can be mounted on the back of a loudspeaker, allowing you to dispense with speaker cables. Near field they will only need a single ended interconnect from an unbalanced source, but at lengths greater than 5 metres balanced cables used in conjunction with a balanced source is advisable.

Even if you don’t want to use them like this, the XLR input allows you to use them balanced or single ended. But for remote or normal use the beauty is the individual volume controls allowing you to adjust for stereo balance for your room – a feature many preamps simply don’t have.

Leave It On And Forget It

It’s designed to be powered on continuously – always on active duty.

It’s well behaved – can be “plugged live” at input, power supply and speaker terminals without being upset in itself, and depending on source preamp, without “thumps” or loud clicks. It’s also very speaker friendly in that it can’t output DC which would otherwise damage speaker voice coils.

Short circuit protection – under no signal the speaker output will withstand a continuous short without triggering any protection. At high volume the power supply will shut down, and the last resort due to a continuous full power short is the fuse filament melting. It is never advisable to intentionally short the output of an amplifier.

And I know I said just four features but I couldn’t resist this one…

It’s A Compact Design Which Means It’s Also “Wife Friendly”