Mozart's Last Symphonies by the Australian Chamber Orchestra in Canberra

Early Saturday evening and Richard Tognetti, Mozart's music still pulsing through his mind, is about to board a ferry to travel home after the ACO's rehearsal. A new project plans a move in several years time from the orchestra's subterranean studios at Opera Quays to a new home at Pier 2/3 Walsh Bay, still so close to the water that is one of the vital elements of Tognetti's life.

This year is Tognetti's 25th as artistic director of the ACO. At just 24 he was asked by Antony Jeffrey, then chief executive of the ACO, to consider leading the orchestra. Had he foreseen anything like this?

"Well, no. You can't prophesy anything," he says, "but it was what I really, really wanted to do in life. But there were some issues and some people were not wholly supportive of a 24-year-old."

Twenty five years on, with the ACO's reputation constantly confirmed as perhaps the best chamber orchestra in the world, it seems that Tognetti has justified his appointment.

Did he feel a compulsion to lead the orchestra down new paths and make his mark from the very beginning?

"Absolutely," he answers. "I had a pretty clear idea of what I wanted to turn the group into and how I wanted them to play and what style to perform in so that was a kind of no-brainer for me. It was just how to do it. There was very little financial help but as we were small we were able to adapt. That's the difference between a big orchestra and a chamber orchestra."

From conventional performances of standard repertoire the orchestra has introduced a stunning spirit of innovation and originality, with the introduction of multimedia in concerts like The Reef (which will be taken to the US after performances in Sydney in February) Gallipoli and the collaboration with Michael Leunig in Carnival of the Animals.

"Some of the best things over the years have been meeting and working with people like Michael Leunig, Neil Finn and Bill Henson," Tognetti says. "I'm really challenged by that, just creating a band of like-minded, really intensely musical colleagues. And we've been a pretty stable group at the ACO and we all love doing what we do."

The orchestra's year is now packed with tours Australia-wide and international, with festivals, with a flourishing education program and with bringing music to people everywhere through online sessions.

An encounter with an innovative ACO program can be like opening the windows of a fusty room to feel fresh air gusting into every corner. Tognetti answers occasional criticism of the orchestra's embrace of the new and the different with "That's a tired old way to look at life. Beethoven was new in his time ..."

For the orchestra's current tour, Tognetti has chosen to play again the three last symphonies of Mozart, "one of the purist, most abstracted listening experiences we can have" – works with which he began his career with the orchestra in 1990.

"Some people think that No.39 in E flat major – three flats, in three-four time – is something to do with the holy trinity but that doesn't matter: it transcends that," he says. "The main theme has such simple, warm melodic gestures. Mozart uses a lot of what's called musica combinatorial – you get a clutch of really dissimilar themes and you chuck them together in a jumbled way but make them into a cohesive whole and create a symphony, which, you have to remember, was a new form of music in his day. This symphony is the least dramatic but the most positive of the three, the one where you might say he is most at one with himself. Only Mozart could compose the extraordinary effervescence of the last movement."

Mozart wrote only one other symphony – the 25th – in the same key of G minor as No.40. "It's rare to find Mozart brooding in a minor key and it's really hard to play to bring out the drama and to be true to the music," Tognetti says. "It really takes you places harmonically."

Of No.41 in C, "Jupiter", Tognetti says, "This is where Mozart throws all these bizarre, disparate elements together to create a masterpiece. The last movement has six or seven themes that he turns into a fugal pattern. In anyone else's hands it would sound a mess. And then at the end it all comes together in pure ecstasy. It's one of the greatest achievements of humankind."

Will these three symphonies be played differently from the way they were presented in 1990?

"Oh God, yes!" Tognetti says. "For a start I wasn't directing, (the late Frans Bruggen was conducting). I wasn't really ready for that in 1990. This time we have wind and brass players from all around the world joining us to play on instruments that are either originals or copies of those that could have been used in Mozart's time so you've got a different sound and the string instruments will be using gut strings. I love the sound of these old instruments. They give a different sense of proportion. There are no solos for the strings but there are for wind and brass."

So again, at this concert, there will be the sense of adventure and the feeling of excitement that this remarkable orchestra has achieved under the 25 year leadership of Richard Tognetti. It's characteristic that he's chosen to play again the works of Mozart, the innovator and trail-blazer.