Fat Jimmy Amplifiers is a boutique amplifier builder based in Petaluma, California, in the San Francisco Bay Area. The company was founded by Mike Pascale, who launched Vintage Fender Amp Repair before developing his own line of amps. After servicing and analyzing hundreds of vintage tweed, brown, and blackface Fender circuits, Pascale began incorporating the component drift patterns he observed in coveted originals into new builds, using selected NOS (new old stock) parts in key positions to shape the tone.

The lineup centers on hand-wired tube amps inspired by classic Fender designs, with models including the Jimmy Jr., the Gigmaster 20 and 30, the Custom 20, the Avionic, the Jimmy James, the Tone Box, the Tone Machine, the FAT JAC15, 5E3-style Tweed Deluxe and 5F6A-style Tweed Bassman clones, and the Bass Odyssey 100. Power configurations span 6V6, 6L6, EL84, EL34, and 6AQ5 tubes at output levels ranging from roughly 1 watt to 100 watts.

Fat Jimmy has developed a following in the Bay Area jam and roots-rock community, with Bob Weir of Dead & Company among the players associated with the brand. The amps are sold directly and through a small network of boutique dealers such as Destroy All Guitars.

Fat Jimmy has 1 product cataloged on Equipboard, including Combo Guitar Amplifiers. Their gear is featured by 1 artist, with the strongest followings in Rock and Folk, World, & Country. Notable users include Johnny Hiland.