The swarsangam is an instrument originating from India which combines a 4-string tanpura with a 15-string swarmandal. Both instruments are constructed on the same sound box. I gather it's a type of zither.

Descriptions and pictures of the instrument:

https://reverb.com/item/1542375

https://www.accentmusic.com/Swarsangam-p/swrsg.htm

I'm also not sure if they actually invented the instrument or are just a brand which makes it today, but a lot of my searching connected it to Rikhi Ram. Kala Kendar describes it as having been "initially designed" by Bishan Das Sharma, son of Rikhi Ram himself (https://rikhiram.business.site/posts/1373652810715517028).