Go back in your mind. Way, way back. To when music was something you felt rather than analysed, thrilled to rather than thought about. To when its power was visceral and real and had nothing to do with posturing and everything to do with passion. To when, ultimately, music mattered most to you.

Now, correct me if I'm wrong, but I reckon that the bands or artists who made you feel that way weren't post-modern pop tarts or lo-fi noodlers. They weren't faceless and they never mumbled the words "we make music for ourselves and if anyone else likes it, that's a bonus." They almost certainly thought they had something worthwhile to say and that the world should listen. They were probably a glorious collision of emotion and ego, power chords and poetry, belief and bombast. Right?

Meet JJ72. A singer/guitarist called Mark, a drummer called Fergal and a bassist called Hilary. All on the cusp of their twenties. All overflowing with so much conviction that it threatens to engulf them even in those moments when they're trying to be rational and cool. Epic songs about love and soul and pain and bliss. A single called 'Oxygen' at No 23 in the UK charts. Heavy coverage in the press. A debut album about to be released. They know they're good. They want to be better.

They believe in music. And, however over-earnest it sounds to say so, music needs bands who believe in it.

Rewind. Dublin's Jesuit-run Belvedere College seems an unlikely incubator for rock'n'roll dreams. Three years ago, both Fergal Matthews and Mark Greaney were pupils. Mark had been surrounded by music for as long as he could remember, and was writing some songs on acoustic guitar. Fergal, inspired by Nirvana, was putting a band together and asked Mark to join. This wasn't because of any knowledge of Greaney's nascent creative talents, apparently. Ferg just thought his jacket looked cool. They duo went through a number of bass players before everything clicked with Hilary Woods.

"It just felt right," Mark recalls. "One of the reasons I'm so confident about this band, whether it sounds arrogant or not, is that it felt natural from the start. When I met Fergal and he wanted me to be in the band with him, we both had our own agendas, but the common desire was to do something special. We didn't have to play a note for six months, yet we had convinced ourselves that we were going to do that. I was sure of it, and I'm still sure of it."

We're talking in the chilly evening air outside Dingwall's, a renowned gig venue in Camden Town, London. A few hours later Greaney and co will take to the stage and play a sweaty blinder of a show in front of an audience comprised of the indie cognoscenti and a smattering of famous faces. James Dean Bradfield, Ian Broudie and Suede's Simon Gilbert are among those who arrive to check out the JJs and leave grinning.

For the moment, though, the band are talking about the past three years and, particularly, the mad rollercoaster of the past few months.

Greaney seems to be the strongest personality of the three. He answers most of the questions with unshowy self-assurance. The other two tend to defer to him, though Fergal makes a few humorous interjections of his own. Hilary for the most part remains silent, the occasional insightful murmur being interrupted before its conclusion by the lads. Each time this happens she just smiles serenely. Either she's well used to it, or she's happy to avoid the public gaze. Or perhaps both.

Anyhow, it falls to her to explain how at an early stage the band decided that firing tapes off to England was the best way to advance their cause.

"We didn't have much interest in being part of that clique of 'local heroes'," she says simply. "You get to a certain point and then that's it."

All three members were desperate to break out of the constricting atmosphere of their native city. While other Dublin bands faithfully paid their dues, scrabbling for support slots and the odd Monday night headliner, JJ72 were getting airplay on BBC Radio One. Soon, they signed to Lakota, a Dublin-based subsidiary of Sony.

It's the kind of career trajectory that guarantees the immediate parasitical attention of bitchers and begrudgers. Sure enough, everything about the JJs, whether fact or fiction, quickly became fair game. They were posh. They wouldn't have got so far if it wasn't for their youth. They wouldn't have got so far if it wasn't for their looks. They wouldn't have go so far if it wasn't for Sony's money. And on, and on.

Last year, the band were quoted in in the British press as saying some pretty unflattering things about the Irish music scene. Now, Mark is a little more diplomatic, a little more defensive. But the underlying sense remains the same:

"It was a conscious decision to look more towards Britain," he says. "But it wasn't as if there was any 'malicious' reason behind it it wasn't like we hated home. We just thought that [going away] would be more . . .interesting."

Maybe. But in the current issue of Select he is more blunt: "For us, it doesn't matter that we're Irish at all," he says.

Those sound like the words of a man irritated by the neat-but-lazy notion that any band emerging from this country is merely the latest adjunct to the Official Ireland-approved lineage of Rory, Van, The Rats, U2 et al.

"Yeah, absolutely. The whole notion of those musical influences is a fake one in many ways. I know nothing about U2, I don't own any U2 albums, I know nothing about most Irish bands. It's much more likely that you'll get an influence by accident rather than by having it drilled into you."

"In my case, I saw a clip of Joy Division on Channel 4 at about three in the morning and thought, 'who the fuck is that?' Then I went and found out who they were. Influence happens like that, not by me going out with my friends in Dublin, and us saying 'oh, we all like U2'."

Mention of Ian Curtis' combo brings us to the subject of JJ72's eponymous debut album. Joy Division have been cited comparatively in many reviews, but to these ears that is due more to Greaney's habit of constantly name-checking them than to any real musical similarity.Whereas Joy Division's sound was that of bleak lives lived in suffocating claustrophobia, the JJs are more jagged, affirming and wild.

Greaney's soaring falsetto has also attracted plenty of attention, but truth be told, it's an awesome gift which he hasn't yet developed the restraint to use most effectively. Sometimes it's expressive and joyous, but elsewhere it sounds like an affected amalgam of Bowie, Brett and (Jeff) Buckley.

For all that, when JJ72 are at their best they conjure up moments so powerful that their otherwise towering influences recede into the distance. The likes of 'Oxygen', 'Snow' and 'Undercover Angel' are nothing less than secular hymns. Lyrics fizzing with vitality and longing are borne along by buzzsaw guitars and wrapped up in tunes to swoon for. There's even the pastoral 'Willow' as proof that they can whisper as powerfully as they can scream.

Self-confident he may be but Mark Greaney is wise enough not to oversell his band's accomplishments to date.

"I don't know where it's going to go from here, but I know that the album isn't good enough for what we want," he says. "I can sit down and say, 'yes, it's a really good album', but it's still not anywhere near our potential, I feel."

There are a few other misconceptions which he also wants to put right. One is that he is an heir to Thom Yorke's King of Pain throne, all too keen to show us the depth of his wounds at the slightest opportunity.

"Live, we can be loud and aggressive, but the number of times I've been told that we are an angsty band is beginning to get annoying," he begins. "On this album, there are love songs which can still make me feel a bit . . .funny . . .even if I wrote them. I don't hear much angst. The whole notion that teenagers just write angsty songs is a load of shit."

While we're in the myth-busting business, let's turn our attention to the idea that JJ72, together with Muse and Coldplay, form a triumvirate of Radiohead wannabes who are only filling the gap until the real thing reclaims centre-stage.

"That whole comparison is irritating. Both Muse and Coldplay are great bands, but I think they're so different from us. A Coldplay gig is laidback and very different from the way we are. And Muse are a lot more of a 'show'. It just happens to be that we're around at the same time. If Coldplay dated back twenty years, I don't think anyone would sit us down and tell us that we sound like them."

He has a point. Coldplay's songs are generally more orthodox, tidier, lacking the sprawling ambition of JJ72's. What the two bands have in common, though, is an unashamed emotionalism.

This doesn't just infuse the most potent moments on the JJ's album; to 'connect' with his audience is also Greaney's foremost avowed aim. The dressing up of vacuity and inarticulacy as enigma is not for him. Nor is any attempt to disguise the scale of his band's ambitions.

"I think there are a lot of bands that mean well," he says. "But it's an easy opt-out to say, 'all we want to do is put a lot of honesty into our music'. As far as they're concerned that's enough. It's not.

"If you get honesty and emotion into your music, you have to get it across to people. And, most likely, you'll want to get it across to as many people as possible. We're not one of these bands who would be happy with a few records sold here, a few records sold there," he comments scornfully.

So just how big an impression is Greaney hoping the band will make?

"I'd love to have millions of people connect with it in a big way," comes the artless reply. "I want this band to become a pop band, inasmuch as you can call what we do 'pop music'. It has to have an impact, so that when you're gone no-one's going to be able to eradicate the signs that you were there."

With the album about to be released and the media buzz around the band increasing, momentum is building with every passing week. Nonetheless, the band aren't about to let press attention go to their heads.

"The press doesn't matter!" Fergal exclaims. Mark is more circumspect.

"It's momentary stuff," he muses. "It does have a purpose in that it can make the audience bigger but, at the same time, no-one's going to look back at a page in NME in five years time and say, 'what a page, what an interview!'

It's easy to see JJ72 as a band who are talking it before they can walk it. But to do so misunderstands where they're at. For a start, when the music's good, it's great. Not 'great for a young band' or 'great for a Dublin band' but 100% brilliant.

Secondly, the JJs talk with such earnest aspiration not to hype up what they've already done, but because they're so full of enthusiasm for what they are yet to do.

Yes, there have been many Irish bands who have done the same thing promised great things and delivered nothing. But JJ72's combination of impetuosity, innocence,and conviction added to the sheer luxuriance of their talent might make them different. JJ72 aren't the band they'd like to be yet. They know what they lack. And they want it badly.

"One of the main reasons for a band to keep going or for a person to keep writing songs is that you never get to the promised land," Mark Greaney says. "But that's brilliant, because we keep wanting more.

"I don't want more money, I don't want people to adore me. But I want to be playing to a lot more people and seeing it on their faces making them cry by playing beautifully and just being really good at what we're trying to do.

"I think we have done something special in what we've done so far," he concludes, "but I'm sure we'll do even more special things in the future."

Who would bet against them?

JJ72 is out now on Lakota.