I am just reading a very interesting book - "Beethoven and the creative process" by Barry Cooper. In this I discovered a so far to me unknown sketch probably for a string quartett Adagio, for it is among the sketches for the Cavatine from op. 130. It is very beautiful and the beginning reminds of the Andante from the 3rd mov. from the Ninth. Here is first the original one voice sketch and then repeated again with an additional bass line from me:
www.gerdprengel.de/Beeth_quartett_Skizze_1825_Adagio.mp3
Always something new to discover ...
Gerd