A grand piano built by Wilhelm Wieck (1828-1874), a cousin of Clara Schumann’s, in Dresden has a range of 6 ¾ Octaves (AAA-g’’’’). Since the 1970s it has belonged to the collections of the Robert Schumann House in Zwickau but has never been displayed because it is not in playing condition.
You can listen to an audio sample of Robert Schumann’s aria piano sonata Op. 11 (piano transcription of Schumann’s song ‚An Anna‘) played by Thomas Synofzik on the Wilhelm Wieck grand piano.