SEATTLE, WA — There's a musical instrument as rare and finely crafted as a Stradivarius for sale at a local guitar shop — but this instrument is covered in brown suede and is so loud that it's probably a health hazard.

Seattle's Emerald City Guitars recently acquired a rare Dumble guitar amplifier, and at $159,995, it's likely the most expensive guitar amplifier for sale in the world right now. Why so expensive? The amplifier was made by hand in 1978 by Alexander Dumble, a cantankerous and legendary technician and boutique amp maker. His amps are the rarest and most sought after in the music world. He only made an estimated 300 during his peak (he's still alive, but it's unclear if he's still working), and the Dumble at Emerald City Guitars is the ninth one he ever made. It was apparently custom built for country legend Merle Haggard, the shop says, and that means there's no other amp in the world like it.

"It's a unicorn," said Trevor Boone, the Emerald City employee who acquired the Dumble from a collector in Nashville. Dumble amps, Boone explained, typically pass between a small circle of musicians, collectors and investors. Every Dumble that comes up for sale is more expensive than the last, he said. To the average person, the amp might not look like much. It's a rectangular box a little more than 2 feet long and about a foot high with a bunch of mysterious knobs and switches. Perhaps in a nod toward the country, Alexander Dumble covered the amp in brown suede. All the knobs are labeled with the 1970s "Computer Regular" font.

Dumble No. 9. was apparently made for Merle Haggard and is wrapped in brown suede. The Dumble's set of four 6550 vacuum tubes and massive power transformers give it a ton of power. But it's what's inside that counts. Dumble got his start building electronic devices like radios and PA systems in middle school. In the 1960s, he began modifying amps made by Fender. His first Dumble amps were based on the Fender Bassman circuit (Emerald City has a 1956 one for sale for $11,000). The famous Marshall amplifiers were also based on that Fender model. One of Dumble's first clients was the surf-rock band The Ventures. But Dumble did something different with his designs, and he won't tell anyone exactly what that is. In the 1980s he began painting all the parts inside his amps black to prevent people from seeing exactly how he engineered them. Although Boone said that some people who have opened up earlier Dumble amps have, surprisingly, found ordinary parts inside from Radio Shack.

Quite simply, Dumble's amps sound beautiful. Boone plugged a 1950s Fender Telecaster (the guitar Haggard was famous for) into the Dumble and turned the volume up about halfway. The amp was so loud that the walls vibrated, but Boone's Telecaster still sounded clear and somehow gentle, like a piano.

"It's got a pure, loud, punch-you-in-the-gut tone," said Boone, 27, who plays in the Seattle rock band The Hollers.

Emerald City's Dumble is rated at 150 watts, which basically just means that the amp can get very, very loud, and still sound clear. Amps with lower power ratings will distort when the volume gets too high.

It takes a special kind of guitar shop with expertise in rare items to sell something like a Dumble. Emerald City definitely specializes in rare and collectible instruments. Among the more notable instruments they've had over the years: a Fender Tremolux amp used by Jimi Hendrix; an Ibanez Tubescreamer pedal used by Stevie Ray Vaughan; and even a few other Dumble amps (one was sold to John Mayer).