Graham's Blog Archive

The Proprius "Balancing Act"

Posted by Graham
October 19th, 2012
Proprius mono block amp Image updated July 2016

Some people love balanced audio – some people don’t understand it and shy away from it. Here I’m going to show you how easy it is to understand.

Balanced audio is supposed to be a big selling feature but that’s not the reason why I designed the Proprius mono-block power amp using such an input. I did it so it could be used some distance from the preamp and a balanced feed makes that possible.

But just because the Proprius has a balanced input you don’t have to use it balanced provided it’s sited within a reasonable distance of your preamp – you don’t have to go to the expense of replacing your preamp with one having balanced outputs!

Not a lot of people realise that you can use a balanced input single ended over short distances with no degradation in performance.

The only difficult part is changing the gender of the connector at the end of your phono to phono interconnects…

The DIY man can usually solder on a different connector and the dead-easy instructions are right there on the Proprius rear panel. All he needs is one male 3-pin XLR plug per Proprius.

But if you’re not into DIY cable making a ‘gender changer’ will do the job. It converts from phono (RCA jack) to XLR 3-pin plug. But if you don’t like adapters you’ll want something like our CuSat50 or Lautus phono to XLR cables (CuSat50 pictured below).

CuSat50 phono-XLR

OK, that’s dealt with using balanced inputs with single ended outputs and it wasn’t all that painful was it?

Now, if you do have balanced outputs on your preamp you can use them to connect to the Proprius even at short distances if you want – that’s not a problem.

But balanced audio is really for transmitting an audio feed over long distances such as between your equipment rack and speaker positions. You see, the Proprius can be used at or fixed to your speakers, and I’ll cover that in a coming newsletter. That distance may only be a couple of metres but quite often can be around 10 metres when you include drops to the floor – maybe even longer.

The ‘KISS’ (keep it super-simple) phono to phono interconnects are great for interconnection between adjacent pieces of equipment because a short piece of cable will have a low enough impedance ground or ‘chassis’ conductor – usually called the shield or screen – to keep both pieces of equipment chassis’ at the same potential, thus avoiding hum. However, with long lengths of cable the impedance grows and isn’t as good at holding both potentials together, and hum can result, plus radio interference can creep in.

Enter the slow twisted pair! That’s two pieces of wire twisted together with a twist at around each inch of travel. Any noise picked up is common to both wires. A balanced input ignores common signals and so pick-up noise isn’t a problem. You need a balanced output to feed this type of cable because the balanced input is ‘looking’ to amplify the ‘uncommon’ signal. You’d usually have the twisted pair shielded because the balanced input can’t deal with really high radio frequencies.

This type of cable is commonly referred to as a microphone cable. When you think about it, telephone wires are just this, but without any shield because the telephone filters out all the highs. Telephone wires are long, and often the balanced feed of an outside broadcast will be ‘beamed’ back to the studio using a shielded ‘BT twisted pair’ specially located for such work, under a conveniently placed manhole cover.

That’s the ‘power of balanced’. Not really necessary for short lengths but mandatory for long distances, and that’s why the Proprius can do both on its XLR input.

So, now you know all you ever needed to know about balanced audio to enjoy your music.