Last week at the 92nd Street Y, Julian Rachlin and Itamar Golan presented a rare opportunity to hear all of Brahms’s violin and viola sonatas in a two-part series. Particularly remarkable was Mr. Rachlin’s trick of switching off between violin and viola; musicians who play both instruments at a high level are surprisingly uncommon. But leaving aside the novelty of the endeavor, I found the series to be very much a tale of two concerts.

I left the first installment on Wednesday night quite impressed with Mr. Golan's performance at the piano, but thinking that Mr. Rachlin sounded far better as a violist than as a violinist. Now I should say first that as a violinist myself, I am often particularly critical of my brethren. From the very beginning of the first violin sonata, I found Mr. Rachlin's tone to be forced on the lower strings. There were also minor impurities in his playing at times: little extra noises, imprecise shifts, and the like. These were by no means glaring, but they often came at times when the violin was particularly exposed, which was unfortunate. Now there were times that he let up on his bow pressure and produced a lush, warm sound from the G-string. Moreover, he found a soaring quality on the upper strings with ease, though at times it became a little tight, due mostly to a vibrato that I felt was a bit on the fast side. Mr. Golan at the piano had a sensitive touch and was carefully attuned to his partner; this collaboration felt completely natural. The third movement was the highlight of this sonata, even if it took them a moment to agree on a tempo. Mr. Rachlin's variety of colors here was superb, and although his tone was not always to my liking, his superior musicianship was evident.

Now as a violist, Mr. Rachlin won me from the start. He had a full, dark sound in the first movement of the F-minor sonata. I think we often let violists get away with little things: little scrapes, a constant hiss, a choked quality to the sound. None of that here. This was truly fine viola playing, and there was a wonderful confidence that seemed to be missing from the first violin sonata. Perhaps a bit too confident (“loud”) at the beginning of the second movement, but he settled in nicely by the time the contemplative opening theme came around again. Mr. Golan's descending thirds in the third movement flowed effortlessly, and the two of the jumped directly into the vivace finale with gusto. Mr. Rachlin's playing here was not completely clean, but he took charge; it is easy to let this movement become too dainty, and he certainly did not.

Back on the violin, Mr. Rachlin sneaked in under the piano (not literally, of course) at the opening of the sonata in A major. It was effective, though it foreshadowed somewhat the problems that I heard on the Saturday night portion; more on that later. The tempo was a bit on the faster side, and there was a heroic sort of energy to the performance. Mr. Golan's playing in the development was characterized by a wonderfully wistful melancholy. The last movement lacked conviction initially, but it ended with power.

They closed the program with the C-minor scherzo, an odd choice given that it is far less substantial than the sonata it followed, and was slated for the Saturday night program, as well. They breezed through it nicely; not a terribly nuanced performance, though it was energetic. The two encores, Fritz Kreisler's Liebesleid and Liebesfreud, were charming, and Mr. Rachlin's tone was brighter and more intense than I had heard from him all night. On the whole, I was consistently impressed by the balance the pair achieved; these sonatas must be equal partnerships, and pianists who mouse around under the violin often sap them of their power. Not so with Itamar Golan on Wednesday.

Now fast-forward to Saturday night, for the conclusion of the cycle. The program opened with the exceedingly obscure “F-A-E” sonata, a joint composition by Albert Dietrich, Robert Schumann, and a 20 year-old Brahms. This is a peculiar piece, and does not really hang together particularly well; in fact, it sounds as though it were written by three different composers (imagine!). The marvelous balance I had so admired on Wednesday was gone. Suddenly, Mr. Golan was overpowering his partner in more than a few spots, which was a shame because Mr. Rachlin sounded terrific. His tone was so much richer than it had been on Wednesday, it was almost as if he were playing on a different violin. There was no forcing on the lower strings, his vibrato was crisp without being too fast, and his phrases seemed to have more room to breathe. The second movement was gorgeous, though it's so short that it's gone almost before one notices it. Our old friend, the C-minor scherzo (see above) was better than it had been on Wednesday. At its opening, Mr. Rachlin's playing was strong, gutsy, determined, and slightly out of tune; though I think we can forgive that one offense, as the tradeoff seemed to be the amazing fervor he summoned this time around. The last movement did not sound entirely comfortable, but to be fair, it's written rather awkwardly for the violin. In all, both players brought passion and conviction to what is admittedly an odd piece.

Mr. Rachlin returned to the viola for the sonata in E-flat major, and his tone was just as warm as it had been three nights before. Unfortunately, it was marred by some more intonation issues, and Mr. Golan continued to overpower him. The second movement was sensitive, and the third was handled lightly, but ended with a profound sense of joy.

There is no one right tempo for the first movement of the D-minor violin sonata. At one extreme, we hear an expression of desperate sorrow, and at the other an urgent pleading. Messrs. Rachlin and Golan chose a tempo right in the middle, and the result was a thoughtful melancholy. There was, however, quite a bit more rubato than was necessary. No matter what tempo one chooses for this opening, there has to be a constant sense of forward motion or it simply starts to drag. At the opening of the second movement, Mr. Rachlin's sound was oddly aggressive. In retrospect, I think he may have been trying to overcome his partner's excessive volume, as it was indeed difficult to hear him when he played softly. Still, he was able to find the tender passion required of the music. The third movement was impish, playful, and altogether winning. It took on a commanding feel as the music became darker and more urgent. They exploded into the finale with nary a pause, and the energy was thrilling. After the opening volley, there was a profound sense of exhaustion and then relief. Mr. Rachlin's playing in this movement had a fierce intensity, and the sonata as a whole represented the best playing he did in the entire cycle. Regrettably, so much of it was covered by Mr. Golan's overpowering sound, it could not be fully appreciated. Two more encores, Brahms's first and seventh Hungarian Dances, were performed with considerable flair.

What to make of all this? The difference between the two recitals was at once striking and baffling. A woman sitting to my left accused Mr. Golan of “ruining” the second recital, and further charged that he had “ruined” a recital with Vadim Repin, as well. This evaluation seemed excessively harsh, but I would certainly like to hear Mr. Rachlin again with a different pianist. Or even without one: the Bach sonatas and partitas, perhaps?