CHANGE happens slowly in a band that has been together for 43 years.

Chicago, still with four of the seven musicians who got together in that first year, has gone through the changes cautiously but steadfastly. Most of the 30 albums are numbered rather than titled and rarely have the band members' faces appeared on the covers. For long-time fans still playing the first three albums on high rotation, any change in personnel or musical direction has been accepted as necessary to keep the band going, but a compromise all the same.

The original six formed in February 1967, calling themselves the Big Thing. Peter Cetera joined in December that year, the name changed to Chicago Transit Authority and then became simply Chicago before the first album was released in 1969. Cetera, the bass guitarist, singer and songwriter whose pure tenor voice crooned on the hit song If You Leave Me Now in 1976, always hated Chicago's horns, according to trombonist James Pankow. But Cetera endured them from 1967 until the band's 17th album in 1985, after which he departed for a solo career. His replacement, Jason Scheff, has been in Chicago for 25 years, much longer than Cetera, but older fans consider him one of the "new guys".

Founding drummer Danny Seraphine was fired in 1990 after flagging performances. Seraphine's replacement, Tris Imboden, a 20-year member of Chicago, is another "new guy". Bill Champlin, already a veteran singer, songwriter and keyboardist when he joined Chicago in 1981, departed last year after a 28-year run as a "new guy".

The only sudden change was in January 1978 with the death of guitarist, vocalist and songwriter Terry Kath, from an accidentally self-inflicted gunshot wound. Jimi Hendrix had famously lauded Kath's guitar prowess; his was a distinctive sound that incumbent Chicago guitarist Keith Howland, a 15-year "new guy", emulates adeptly.

The most significant things that have never changed for Chicago are the brass section and the dynamic live shows, and the two are intertwined. Even the most hardened cynics who long ago relegated the band to the annals of power balladry are blown away when seeing a concert by the rock band with horns that was formed by classically trained musicians in the city of Chicago.

The energetic Pankow, 63 – whose compositions include Make Me Smile, Just You 'n' Me,Searchin' So Long and brass arrangements on most Chicago songs – has played trombone alongside Walter Parazaider on woodwinds and Lee Loughnane on trumpet for the entire life of the band. Keyboardist, vocalist and songwriter Robert Lamm, the fourth original member, who wrote hits including 25 or 6 to 4, Does Anybody Really Know What Time It Is? and Saturday in the Park, is a mainstay of the band, debonair and seemingly ageless.

Unlike any other rock band of its vintage, Chicago has never broken up or taken a single year off touring, not even after Kath's death. The band plays about 100 concerts annually; it was many more in the early years. While its international profile was huge in the 70s, the focus since the 80s has been on maintaining its American following, with sporadic overseas excursions. Other than a blink-and-you'd-miss-it appearance at a blues festival in Melbourne in 2004, this will be Chicago's first Australian tour since January 1979, when it filled outdoor stadiums and invited World Series Cricket players on stage to sing C'mon, Aussie C'mon during its Sydney encore.

At that time, only one year after Kath's death, with the first of four replacement guitarists on board, the band was enthusiastically plugging its 12th album, Hot Streets, and the hit single Alive Again, a Pankow composition that purportedly represented its new lease on life.

But in reality the members then were shell-shocked. It took many years and some key line-up and musical changes to work through their shock and grief over losing their musical leader, the "soul of Chicago". Lamm wrote two intensely poignant songs about the loss, which he recorded on non-Chicago albums. Loughnane still chokes with tears when talking about the circumstances of Kath's death. But the trumpet player, who turns 64 next month, is sanguine about the present line-up and does not feel the band needs to explain itself to Australian fans who have not seen Chicago for 31 years.

"For me, the march continues, and what we have managed to do is put a band together that is as good as, or better than, what we started out with," says Loughnane. "When Terry passed away he wouldn't have wanted us to stop, and we knew that. So we kept going and we hired somebody else to take his place. From then on when there was a change that had to be made, we made it, because we love doing this. We are a good road band, we love playing, we love making records, we love performing."

The last album of new material, Chicago XXX, was released in 2006. But most of the memorable songs in Chicago's vast catalogue are from its early years. From its audacious 1969 debut double-album Chicago Transit Authority to Chicago VII, the tracks were politically charged, emotionally earnest and musically edgy, fusing rock, classical and jazz. Then, with Chicago X and the Cetera-written hit If You Leave Me Now, radio programmers decided Chicago was a ballad band and wanted more of that.

After Cetera's departure, the ballads flowed from newer members Champlin and Scheff, or hitmaking writers-for-hire such as Diane Warren. The songs won new fans and some producers and record companies wanted to drop the horns altogether. Says Pankow, "We've been fighting the perception of what pop music should be, and it doesn't agree necessarily with my perception of what pop music is, and it doesn't necessarily agree with my perception of what the role of brass is in our music. I've always wanted to approach the brass as an equally important lead voice that is interwoven throughout a song, not as frosting on a cake, but as an integral part of the arrangement."

Lamm, about to turn 66, is often forthright about his frustrations with Chicago's direction and has been the most active outside the band, releasing seven solo albums plus a tenderly rendered trio record, Like a Brother, with Gerry Beckley of group America (touring with Chicago in October and November) and Carl Wilson of the Beach Boys. "I'm much happier with the power of lyric writing I've accumulated over the years versus something like Beginnings or Does Anybody Really Know What Time it Is," Lamm says.

Fortunately, a Chicago concert nowadays features fewer ballads and more rock. On stage the horn section is placed firmly in front and the "new guy" rhythm section of Scheff and Imboden is forceful. The 100,000 Australian fans who flocked to see Chicago in 1979 would be well advised to check it out in 2010, says Loughnane.
"Amazingly enough, I'm able to do something that I started doing when I was 11 years old, and with the same guys, basically, four of the six men I got together with when I was 20 years old. I have to pinch myself. How the hell did we possibly do that? I think we're pretty good at what we do, or we would have been gone a long time ago."

Chicago performs with America and Peter Frampton in Sydney, October 27 and November 6; Canberra, November 7; Adelaide, November 9; Perth, November 12. With Brian Wilson, America and Frampton in Wollongong, October 29; Brisbane, October 30; Melbourne, November 1 and 3; Hunter Valley, November 6.