4-string cello by Nicola Gagliano, 1770-1780. Kindly on loan to Vladimir from the Jumpstart Jr. Foundation
4-string cello (after Gofriller), Clive Morris, 2010. Reversible conversion to five-string cello by John Topham, 2013
Small 4-string cello (after a viol by Gasparo da Saló), Philippe Refig, 1997. (a similar instrument can be seen in this painting by El Greco)
7-string viol (Colichon model), Jane Julier, 1994