The 1726 Stradivarius violin was purchased by ACO chairman Guido Belgiorno-Nettis and his wife Michelle before the couple announced this week they would give it to the nation's orchestra for long-term loan.

The violin will make its public debut when ACO principal violinist Satu Vanska plays Beethoven's Romance in F major during the Nicole Car concerts when the show tours nationally in April.

"You have to keep a cool head and you can't fall in love with these sorts of instruments straight away," Ms Vanska told AAP.

Ms Vanska said the violin went through vigorous testing, including in big concert halls, to measure the instrument's ability to carry sound. It was also compared with other fine-string instruments.

"(This Stradivarius) has a very clear, diamond-cutting-like sound, with golden and velvety tones," she said.

"It is a very powerful-sounding violin and you can play it very softly or very loudly or anywhere in between and it always carries."

The ACO wouldn't say what it paid for the violin, stating only that the value of the instrument rests in its artistic history.

But a 1726 violin by Stradivari sold at the prestigious British auction house Christie's fetched STG49,500 ($A97,020) in 1978.

The violin is among only 650 Stradivarius which have survived from what is today known as the Golden Period of violin making.

Antonio Stradivari tinkered in his workshop handcrafting violins, guitars, cellos and violas in the north Italian town of Cremona before his death in 1737.

The Australian Chamber Orchestra now holds the only two Stradivarius violins in the country. The ACO Instrument Fund bought a 1728/9 version for $1.79 million in 2011.

Australian Associated Press