NEW YORK – When Brian Johnson got the news that AC/DC’s new album had debuted at No. 1 in America – and in more than two dozen countries – he didn’t pop any champagne.

Instead, the lead singer of one of the world’s biggest rock groups celebrated alone, in a modest hotel, with a plastic cup of wine and a cheese sandwich. He was preparing for a tour.

“It (is) kind of ironic, isn’t it?” laughs Johnson, who had been staying in Wilkes-Barre, Pa., where the band kicked off their recent tour last month. “I wasn’t promenading down the street … none of that. I was sitting in a little room.”

“I think it typifies AC/DC basically, it’s just what we’re like,” he says of the low-key celebration. “I guess I like it that way. We always keep our head below the radar, always have been. Now, there’s nowhere to hide!”

Not that Johnson is seriously interested in taking cover after the huge success of “Black Ice,” the group’s first studio album in eight years. The CD, released exclusively at Wal-Mart and on the band’s Web site, sold nearly 800,000 copies in its first week in the United States, making it the second-best album debut of the year, second only to rapper Lil Wayne (the CD has already gone platinum).

While AC/DC is not unaccustomed to topping the charts – they’ve sold 70 million records in the United States alone over their decades-long run, placing them 10th on the all-time list of best-selling acts – they are enjoying their greatest success, and exposure, in years.

“It’s definitely their biggest return to form in many years,” said Jason Fine, executive editor of Rolling Stone, which put AC/DC’s Johnson and the group’s founding members and leaders, guitar brothers Angus and Malcolm Young – on a recent cover (guitarist Cliff Williams and Phil Rudd round out the group).

“It’s their best record since ‘Back in Black,’ since 1980,” added Fine. “Unlike some of the records that they made over the last 20 years, this one really sounds alive.”

Part of the credit goes to acclaimed producer Brendan O’Brien, whose credits include albums by Bruce Springsteen, Pearl Jam and Rage Against the Machine. Once Angus and Malcolm crafted the songs for the CD, O’Brien geared the sound toward more of the rambunctious, carefree rock sound that made songs like “You Shook Me All Night Long” such enduring classics.

Sitting in the offices of the band’s label, Sony Music, the slight Angus, wearing a T-shirt and jeans, talked about O’Brien’s impact on the record. The producer thought the band’s last two CDs were more blues-based.

“So he was trying to recapture more of that rock sound, like the ‘Highway to Hell’ – he said he even liked the ‘Dirty Deeds (Done Dirt Cheap)’ time,” says Angus, referring to two of the group’s seminal discs.

“It has to sound like AC/DC. You want them (fans) to hear that and go, ‘That’s AC/DC.’ … But you also want them to hear it and go, ‘But it’s AC/DC playing something new.’ That for us is always the challenge. You hope that your songwriting, the way that you’re doing it is getting better.”

“They do something very unique in (that) they have a way in presenting very aggressive music but almost in a kind of catchy, hokey way, and I just felt like my favorite music that they’ve done has been that kind of music,” O’Brien says. “My thinking was, ‘If I can just help people when they hear it remember how great this band is, then that’s a service to them.'”

It’s not as if AD/DC had been toiling in obscurity over the last few decades. Their 2000 CD, “Stiff Upper Lip,” had respectable sales and is now at nearly 1 million copies sold, according to Nielsen SoundScan. In 2003, the band was inducted into the Rock and Roll Hall of Fame.

But their glory years were in the late 1970s and early 1980s, when Angus and Malcolm’s pioneering, gritty guitar riffs helped forge a new era in rock, and their outrageous antics (Angus still dances on stage in a schoolboy suit, though his mooning days may be over) helped propel the band to stardom.

For all their success, they’ve never received much critical acclaim; in fact, the band was more likely to be derided and ignored than celebrated.

Even Fine acknowledges as much on Rolling Stone’s part. When he was considering putting AC/DC on the cover, he went to the magazine’s archives to research articles on the band.

“Literally the last story that we did on AC/DC that was of any size was in 1980,” he says. “We had literally not covered the band at all. We did very few short news stories, and Rolling Stone was not the only one. AC/DC was never a band that was really covered a lot by the critics, they were always kind of looked down on.”

If Johnson, who spoke by phone, has any complaints about AC/DC’s career, that may be the main one.

“The critics have always been a little flippant with AC/DC about Angus and the school suit, and it’s always easy to have a quick little joke or a dig at the expense of it, the easy riffs, and such and such, and they’re all dead wrong,” he says. “The easiest riffs in the world are the hardest ones to write, because they are very few.”

“‘Highway to Hell’ is easy, but you ask a guitarist, it’s not that easy,” he adds. “Nobody can write them because easy things are very difficult to write … and to put them together in different computations and to come up with something fresh and different. It’s genius, but the critics never figure that out.”