This instrument evolved from the Afghan rabab and the similarities are structural and therefore, technical as well. There may have been some influence of the vina, but the connection with the Afghan rabab is stronger. The sarod itself emerged in the nineteenth century and there are contesting claims to the form of the sarod as it is now, Keramatullah Khan, author of Najmat Niamat claims his father Niamatullah Khan is the creator, whereas other believe Gulam Bandegi Khan Bangash modified the Afghan rabab into the sarod. His son Ghulam Ali is mentioned as one of the first sarodiyas (sarod player).
Another instrument known as the sursingar has physical features common to both the sarod and the Afghan rabab, and it antedates both.
Structurally, the sarod is made out of one block of wood, has a short body, a hollowed out belly partly covered with parchment, a longish tapered neck that ends in a peg-box. The fingerboard of eighteen inches is over the belly. The peg-box has six or eight openings for tuning pegs.
In the traditional sardo, there are six main strings, five of which are melody strings and are played by stopping. The sixth string is supplementary and can be played open or as a chikari string since it is tuned to Shadja. Two strings at the upper end are the true chikari (i.e. for rhythm and drone), while eleven to fifteen sympathetic (taraf) strings are situated below the main strings.
The Maihar gharana sarod has a larger number of strings, and the stringing is at three levels - the main strings, chikari and one supplementary string at the topmost level; three supplementary strings at the next level; the remaining sympathetic strings at the lowermost level. These last three strings are strummed and are tuned to the main notes of the raga. The traditional sarod has strings at two levels. However, in both instruments, the strings are attached to the langot on the lower end of the sarod.
Ustad Allauddin Khan of the Maihar gharana played both alap and the gats on one and the same instrument which was modified for the purpose by his brother Ustad Ayet Ali Khan.
The latter innovated the use of separate bridge for the supplementary strings, a greater number of taraf strings, enlarging the resonator, bringing in a brass resonator, changing bridge structure, and introducing the plectrum made of coconut shell wood. These improved the quality of sound. Previously, only gats could be played on the sarod, and the alap was confined to the sursingar.
The sarod does not allow for much creativity except in the manner of plucking the strings. This however, has led to a variety of bols coinciding with the freedom thereof. There are no frets on the sarod, and this together with the increased number of strings vis-a-vis the sitar means that many tăns cannot be played. The forearm comes into use while playing the sarod, thereby imparting a freshness to the performance.
Initially, double stroke tăns were played on the sarod because of the limitations of an unfretted instrument. Single-stroke tăns known as ekhara tăns were included in the sarod repertoire much later, and first played by Ustad Hafiz Ali Khan and Pandit Radhika Mohan Moitra. Ekhara tăns require quick finger movements on different strings. These tăns are now close to the speed of vocal tăns, and are played to perfection by Ustad Amjad Ali Khan.