I found this site the other day, searching for tanpura samples. There are high quality stereo recordings of drones in each key, as well as information on history and construction of the instrument. It’s fun to just trip out on listening to the cosmic harmonics:
Tanpura samples: divine Indian drones in all 12 keys
There is also a lot of other great content on the Rāga Junglism site (and YouTube channel).
What makes the tanpura sound so cool is the nonlinear effects of the strings rattling against the rounded bridge, with the vibrational damping being fine-tuned by a tiny thread. This javārī sound is the same phenomena that makes the sitar and other classical Indian instruments sound so magical.
For those interested in the physics of the instrument, this is an awesome paper: Walstijn (1996). A Real-Time Synthesis Oriented Tanpura Model.