SINGLE ROPE FOR CELLO Single string for Cello D'Addario Kaplan Solutions KS511 4/4 Heavy A (A). Solid steel core with titanium wound. Kaplan Solutions Cello A and D strings produce a full, rich, and warm tone. It has been designed to allow greater projection in the highest register of the instrument, balancing and mixing the lower strings well. Designed for professionals, it stays firm under high arc pressure, and provides a strong tone, for solos, without being too bright.