By the end of his life, Beethoven had composed nearly seventy sets of variations. Most of the early ones were based on themes by other composers and were not given opus numbers, which Beethoven reserved for what he felt to be his more substantial, important works.
An occasional piece, Beethoven's WoO. 75 Variations are based on a theme from Peter Winter's (1754-1825) Das unterbrochene Opferfest, which premiered at the Karntnertor Theater in Vienna on June 14, 1796 and played for several years afterward. The quartet, "Kind, willst du ruhig schlafen?" became particularly popular, inciting Beethoven to composed and publish a set of variations based on it in the hopes of making some money. Two other variation sets of 1799 were inspired by operas: the publication of the Variations for piano in B flat major on "La stessa, la stessissima" from Salieri's Falstaff, WoO. 73, appeared in February 1799 and the Variations for piano in F major on "Tandeln und scherzen" from Sussmayer's Soliman II, WoO. 76, was announced in December of the same year. The Variations on "Kind, willst du ruhig schlafen?" were published in December 1799 by Mollo & Co. in Vienna.
Although Winter's tune, in F major and 2/4 meter, is built around only three harmonies, it is quite long and its second half contains variations of the first. The arpeggio outlined by four eighth notes in the first measure takes on particular importance in the ensuing variations, the first of which increases the intensity of the theme through a constant sixteenth-note motion. Technical display is the salient feature of the second variation, in which Beethoven adds a few chromatic touches to the melodic material. The third variation is an essay in free invertible counterpoint while the fourth reduces the dynamic level and becomes more harmonically adventurous. Only the general shape of the theme remains in the imitative fifth variation, closing with material broken between the hands. The most straightforward presentation of the theme yet occurs in variation No. 6, in F minor, although Beethoven inverts a few measures of the melody. A shift back to F major brings with it a 3/4 meter and the final variation, which is in two parts. Here, the shape of the theme is clear, although it is extended and developed in a Beethovenian fashion. After a return of the 2/4 meter, the theme appears clearly, but on D major, and Beethoven spends the rest of the piece modulating back to F major before a lengthy trill initiates a coda that further varies the theme in the left hand.
(All Music Guide)