What happens when a member of the orchestra becomes the conductor?

How much does rank-and-file experience count for on the podium? And - the big question - should he still go to the pub with the musicians after a concert?

It has been a year since Thomas Sondergard, once timpanist of the Royal Danish Orchestra, arrived as principal guest conductor of the Royal Scottish National Orchestra. He became BBC National Orchestra Of Wales's principal conductor at the same time, and in the past 12 months there has been something of a quiet bond taking place in the concert halls and rehearsal rooms of Cardiff and Glasgow.

Audiences admire Sondergard's cool, unshowy insight: he is the kind of conductor who does not make a fuss, whose stage presence is understated but always communicative. Musicians respect his clarity and formidable ears. He earns focused and stylish playing from his orchestras - and if he is building trust with them, he says it is because he respects the fact he is not their colleague any more.

I meet Sondergard on a rainy Monday at the start of rehearsals for his new RSNO season. Striding through the hotel lobby, the 44-year-old is the picture of Danish good looks: blond curls, blue-grey eyes, smart dress sense. He is just in from Copenhagen where he lives with his partner, an opera singer.

As someone who is always flitting between time zones, does he manage to take proper time off? "Conducting is as much about humanity as it is about studying scores," he answers with soft, weighed precision. "So time off to engage with the world is important. I have always been hungry for inputs. Even time on buses or planes is useful to just look out of the window and think."

There is something wonderfully and wholesomely Scandinavian about Sondergard. He grew up in a small town in central Jutland where the local library supplied all the recordings and scores his inquisitive mind could devour. He knew he wanted to be a musician from the age of about seven: "Whenever I heard music on the street - a marching band or something - I would have to find it and watch. I said to my parents, 'I like to be a part of that'."

At 10 he was sent on the first of several stints of work experience, part of every Danish child's education He chose to spend a week sitting in on rehearsals for Strauss's Elektra at the Royal Danish Theatre.

At 15, he began travelling regularly into Copenhagen to study percussion, but also to teach. "It paid the travel," he explains. "I was ready for it, and it gave me the opportunity to get to the capital and into the opera house. That is where I wanted to be: as close to the pit as possible."

He did well as a percussionist, landing places in top youth orchestras (including the European Union Youth Orchestra) and eventually a job in the Royal Danish Orchestra.

But the shift to conducting was always inevitable. "Even though I really worked to get that job, even though it was secure and well paid, with a pension, with great musicians who felt like a family ... Even though things were a lot calmer then than they ever will be as a conductor."

Does he miss playing? "Very rarely. In a way it is strange not to physically create a sound any more, but now I make sounds with gestures. What I realise is how different that sound can be if there is good chemistry between orchestra and conductor."

And there is the nub: how to concoct the right kind of chemistry. Sondergard says there are no tools, no tricks. "What I do know is there is no fake way of doing it. I try to be myself and to be honest. I try to show musicians I am only there for one thing, and that is to make music together. Power is not interesting for me: there are some old-fashioned conductors for whom power is 80% of why they are holding a baton. Playing in an orchestra taught me a lot about how not to behave."

Didn't playing in an orchestra also grant him some sort of lasting camaraderie with the musicians he now conducts? He shakes his head. "When I started conducting people warned me: don't think you can be the same person as you are privately. Occasionally I will have a whisky with the RSNO musicians after a concert. But lots of orchestral players would prefer not to get to know their conductor. To them, I am the boss for the week and they do not want to reveal themselves to me. That is okay."

He might not be paying their wages, but that does not make him the same thing as a colleague, he says. "Whether I like it or not there is power involved. I could ruin someone's day, week, year or life by saying something careless in a rehearsal in front of all their friends. So I understand if there needs to be some distance."

The vulnerability goes both ways, of course. "Try standing in front of 80 people with all the seats turned towards you, everyone expecting you to talk and do gestures that will make them play beautifully. There is a body language to conducting that I am judged on minute-for-minute."

It sounds draining. With so much hanging in the balance, Sondergard says the chance to build solid relationships in Wales and Scotland is a huge plus. "All that stuff becomes less of an issue the more we get to know each other. Less energy needs to be devoted to how we communicate; more energy can be devoted to the music."

Thomas Sondergard conducts the RSNO at Caird Hall, Dundee, tomorrow, Usher Hall, Edinburgh (Friday) and Glasgow Royal Concert Hall (Saturday)