HEADLINING Belladrum Tartan Heart Festival this week marks the first time Chvrches have played Scotland outside their hometown in many months. The synth-pop trio performed at the Hydro back in February; Lauren Mayberry, Iain Cook and Martin Doherty ripping it up in front of thousands before collaborating with the BBC Scottish Symphony Orchestra for a monumental version of Miracle from Love Is Dead, their most commercially successful album to date.

“It’s nice to try different things, a bit of an alternative take on a song, especially when the album has been out for a while,” says Mayberry. Her soprano – vulnerable but vigorous – more than stood up to the occasion, and her pipes will resonate across the Scottish capital on August 11 when Chvrches headline a Summer Sessions gig.

Although credible and chart-friendly, Chvrches have yet to serve an ace of their own into the top 10, but their bittersweet, electro-pop symphonics changed the mainstream landscape earlier this decade, while their relentless touring schedule has won them devotees around the world.

“No show is ever the same,” Mayberry says. “That’s because each has different people at it. It’s like a feedback loop of energy, the way people respond – it makes you play differently. We’re a very lucky band in that sense.”

Their hook-up in late 2011 seems less happenstance, more strategy. Doherty, then a touring member of The Twilight Sad, decided to channel his creativity into a new project with producer Iain Cook. The pair – once both touring members of the still-missed Aereogramme – had first met while studying music at Strathclyde University seven years previously.

As he told the Guardian last year, The Twilight Sad – who play Glasgow’s Bellahouston Park on August 16 with mentors The Cure – hadn’t been keen on Doherty writing for the band. “I thought: I’ll just write my own songs, then. And that was it,” he said.

Mayberry was already a known quantity. An accomplished musician in bands since her teens, the charismatic young woman also headed TYCI, a respected feminist music collective and fanzine. Their first months working in a Glasgow basement studio quickly bore fruit, with debut single The Mother We Share, an unconventional banger with massive hooks, intriguing lyrics and a cool, DIY aesthetic.

Breakthrough track Recover followed, and throughout their subsequent, self-produced albums The Bones Of What You Believe and Every Open Eye, Chvrches have grappled with two forces: their experimental, introspective indie roots and their love of arena-sized pop.

Like the Scottish weather, bright euphoria is always undercut by melancholy: the knowledge that everything may change in an instant. They discussed that duality before writing Love Is Dead, the first album they wrote as a unit sharing the same space and their first working with others.

After sessions with The Eurythmics’ Dave Stewart, they approached Greg Kurstin (Adele, Sia), who ended up co-producing two thirds of the LP. Their new openness suits them, the trio collaborating with The National’s Matt Berninger to shivering effect on My Enemy, a track that smoulders with the same heartbreak, romance and sense of possibility as New York, Mayberry and Doherty’s home-from-home for the past few years.

Where they go after this year’s high-profile collaborations with US musicians Lauv and Marshmello – whose Here With Me finally got them an indirect top 10 hit – is uncertain. “We don’t have immediate plans,” says Mayberry. “But as we write and produce everything ourselves, we decide what we do and when we do it.”