In a dusty, crowded corner of south Kolkata, India, is a quaint 73-year-old musical instrument shop that easily goes unnoticed. Nobody chances upon Hemen & Co – you have to know it’s there. A no-frills, dilapidated facade conceals its worth: the shop has produced sitars, sarods, violins, guitars and more for musicians including George Harrison, Yehudi Menuhin and Jethro Tull’s Ian Anderson, plus Indian stars such as Ravi and Anoushka Shankar.

Sitars in Hemen & Co are wrapped in plastic and hung from the ceiling with wires. Paint peels off the walls. At 180 sq ft, the shop is tiny; being right on the main road, dust is inevitable. Outside the shop, buses screech to a halt as the traffic lights turn red. The smell of fresh chai lingers as rabindra sangeet chimes from a speaker somewhere in the distance. A second branch down the road is only slightly larger.

Banshi Lal Pramanik has worked at Hemen & Co since 1985. Photograph: Chandni Doulatramani

Each handcrafted instrument is made to order and the owners of this family business, Ratan and Tapan Kumar Sen, only repair instruments they create. While each instrument has a one-year guarantee, they should last a lifetime. The wood for the sitar is brought especially from Assam, while the goatskin of the sarod comes from Kali temples that practice the sacrifice of baby goats. In most temples, sacrificing is prohibited, making it difficult to procure and consequently expensive – it takes a whole month to create a single sarod or a harmonium.

“We don’t look at this job as a business,” says Ratan. “We are professionals, but not businessmen. Money is important but the quality of instruments is more important. We want our business to remain niche to maintain that quality. Staying low-key has worked for us so far and there’s no reason why it shouldn’t in the future. Our father has instilled in us his passion for music, which is unlikely to ever die.”

Ratan and Tapan started helping their father, Hemendra Chandra Sen, as boys, and took over the business after his death in 2010. Hemendra had started the business more than half a century earlier. He had been playing the sitar since he was 10, and at 17 moved to Kolkata from Comilla, Bangladesh. He trained under sitar player Baba Allauddin Khan; when Hemedra’s sitar strings broke, he taught himself to repair the instrument. Impressed by his skill, Khan gave him a chance to service all his instruments and those of his group, Maihar Band. A year before India gained independence from British rule in 1947, Hemendra, then 20, started his business, creating and repairing the sitar, sarod, tanpura, tabla, harmonium, flute, violin, and esraj.

Ravi Shankar became a loyal customer in the mid-60s. When his sitar strings broke, Hemendra repaired the instrument but didn’t charge him. Shankar sent a portable tape recorder as thanks. “His relationship with my father wasn’t just transactional,” says Ratan. “They were also very good friends.” Hemendra taught Ratan how to make Shankar’s specific kharaj pancham sitar.

George Harrison carrying his Hemen & Co sitar off the plane at Heathrow airport, June 1968. Photograph: Mirrorpix via Getty Images

Hemen & Co also counted all four Beatles as customers. George Harrison bought a sitar from Ratan and his father in 1968 – Ratan didn’t get Harrison’s autograph because the transaction was so rushed, an opportunity he regrets missing.) Two years later, Harrison asked Ratan to send him two acoustic guitars. Ratan sent them via Ravi Shankar’s secretary; Harrison, a disciple of Shankar, lived with him at the time. Ratan didn’t take any money from Harrison – in return, Harrison also sent him a huge German-made tape recorder as thanks.

Ian Anderson of Jethro Tull, whom Ratan describes as Lord Krishna for his ability to stand on one leg for hours and play the flute, had met Ratan in 2008 when he came to perform in Kolkata. Anderson played a metal flute, but Ratan gifted him one made of bamboo: Anderson has since bought over 100 flutes from him. Ratan wishes his father was alive to tell these stories. “People lovingly called him He-Man. And he truly was.”

Star power can only carry you so far: Hemen & Co has endured thanks to the loyalty of its clientele. “My father wasn’t just friendly with celebrities,” says Ratan. “He was well loved and respected by everyone including the chai wala and neighbouring shop owners who had known him for decades.”

The shop has several third-generation customers, including 46-year-old Sougata Ganguly, a sarod player. He’s been a regular since he was a boy of seven – his tabla-playing father and grandfather bought all their instruments from Hemen. Now, Ganguly sends his students here. “Their structure, their finish,” he says, “there’s nothing like Hemen.”