A fully Classical-era concert may seem like a straightforward thing: all those clearly defined structures with plenty of melody and easily understood harmony. But underneath that benign exterior, dangers lurk and opportunities abound. Both were evident from the start of last night's concert at Riga's Great Guild Hall, with Sinfonietta Riga led from the violin by Il giardino armonico's Enrico Onofri.

We saw a chamber orchestra format (6-6-4-3-2 strings plus harpsichord, with violins and violas standing), augmented by various configurations of wind players. The opener was Mozart's Symphony no. 10, written when he was just 14. From the outset, it was clear that we had a very tight, well drilled string orchestra: powerful accenting combined with lovely singing lilt to bring through Mozart's youthful verve. Onofri is a charismatic figure on stage: you can see the players respond to his movement and energy and hear the results.

Not everything worked. When horns, oboes and bassoons joined in, their sound didn't blend into the string mix; rather, the wind notes seemed separate and somewhat disconnected. Riga's Great Guild Hall is a good hall for this kind of music: it's spacious, high ceilinged and the acoustic has plenty of warmth and no muddiness. But it's also lively, and the string sound comes through with strength. I wondered why the harpsichord was there at all, since all I could hear of it was an occasional jangle. 

With the winds absent, the string strength was more audible still in the opening of Charles Avison's Concerto grosso no. 5, after Scarlatti. Its portentous, heavy footed opening was impressive, giving way to powerful melodic lines standing above a falling minor key figure and moving to a brilliant Allegro with exciting semiquaver runs. I didn't get much of the Concerto grosso feel of well defined seperate instrument groups, but the music had plenty of interest none the less.

Still without winds, the strings were joined by timpani for Mozart's Serenata notturna, written seven years after the Tenth Symphony. Mozart's gain in maturity and confidence was clearly audible, as a central group of two violins, viola and double bass gave us unusual patterns of sound, a section of pizzicato strings and timpani added particular fun and a vigorous second movement displayed an abundance of Mozart's impish musical jokes. In the rondo, Onofri gave a solo (jazz quartet style) to each of the principal viola, double bass and even timpani (the first drum solo I've ever heard in a Mozart concert). But in this work again, there were problems of balance, with timpani far too prominent and unbalancing the sound.

But those problems vanished after the interval. In Joseph Martin Kraus' overture to Voltaire's play Olympia, the first big chord put us firmly in Sturm und Drang territory: now, we had wind players blending perfectly, excellent changes of pace and a beautifully executed shift into sunnier climes before returning to the stormy weather of the opening. A finely executed closing fade-to-black showed off the Sinfonietta Riga at their best.

Giovnni Paisiello's opera The Barber of Seville enjoyed success in its day before being eclipsed a few decades later by Rossini. The overture is rather more refined than Rossini's, but I'm not sure it makes a good concert piece: its ending (not unreasonably) feels to me like the right point for the opera to start, rather than being an end in itself.

The best was left till last, with Haydn's Symphony no. 44 in E minor. I'm not sure its sobriquet Trauersymfonie (“Mourning symphony”) is well merited: the opening is a serious theme but not unduly dark, and there's plenty of sunshine in the movement as it repeatedly returns to the opening, rather in rondo-fashion. I loved the gentle horn calls which permeate the movement.

A broken string caused Onofri to discard his violin and concentrate fully on conducting, but this seemed to me to serve only to redouble his energy and the way in which it was transmitted to the musicians. The second movement minuet was gracious with woodwind colour enhancing a lovely trio section, the third movement Adagio swelled gloriously – Christmas music to calm a troubled soul – and the Presto finale may not have been marked con fuoco, but that's certainly how it was played, with plenty of vigour to send us off in style.