1975 Dobro Ampliphonic Mandolin

Imagine a world without electrically amplified instruments. In order to be heard by a large audience, you’d need the loudest acoustic instruments you could get – probably a trumpet or a banjo. It’s not surprising, then, that brass instruments and banjos were the backbones of countless bands in the 1920s and 1930s. Guitars just couldn’t keep up; even the biggest, loudest archtops were often drowned out in the cacophony that emanated from bandstands. Today, the seemingly natural solution is to connect a guitar to a loudspeaker. This is done using a pickup of one kind or another (or occasionally a microphone) to transmit an electrical signal to an amplifier whose speaker cone turns the signal back into sound waves. Before this innovation was sufficiently refined for public consumption, however, an intermediate step was proposed: put a loudspeaker inside a guitar and transfer the energy directly from the strings to the speaker cone.

This was the idea created by George Beauchamp and John Dopyera in 1927: the resonator guitar. The resonator itself is a thin aluminum cone that acts as a loudspeaker. The energy of the strings is transferred through the bridge to the cone, causing it to vibrate. This invention was the raison d’être of the National String Instrument Company, founded in 1927. The first National designs used a tricone setup: three smaller cones in an offset arrangement connected by a T-shaped bridge. This did indeed create an extraordinarily loud guitar with incredible sustain, but it had one major drawback: it was expensive.

John Dopyera soon split from National (which his brothers Rudy and Emil continued to run) to form the Dobro Manufacturing Company in 1928. Dobro created a more affordable resonator system with a single large cone. The bridge contacted the cone at the center and also at the edges via eight legs – hence the appellation “spider” bridge. The spider design created a different tone from the tricone, a more nasal sound that has become the standard for all resonators used in bluegrass music. National created its own single-cone design in response (called a “biscuit” bridge) which has become one of the signature sounds of early blues recordings.

The two companies merged in 1935 to form the National-Dobro Corporation. Note that none of the company names explicitly referenced guitars; they all built mandolins and ukuleles as well. National built biscuit-bridged mandolins with metal bodies, while Dobro built spider-bridge mandolins with wood bodies; the tones of each are very different. The National instruments were generally more sturdily built, and are more highly regarded by collectors today. However, the Dobro instruments have their fans as well. Rudy and Emil Dopyera formed the Original Musical Instrument Company (OMI) in 1970 to continue building National and Dobro-style guitars, and in 1975 they started building mandolins as well.

The newer mandolins used a spider-bridge system like the original 1930s Dobro designs, but they were built to much higher standards of quality, sound and playability. The new mandolins were built with mahogany bodies; there were a few mahogany Dobro mandolins built in the 1930s, but most were birch. The bodies were redesigned to be much deeper, giving the instrument a huge, warm voice that contrasts pleasantly with the recent biscuit-cone mandolins by National Resophonic. As with guitars, the spider-bridge mandolins have longer sustain and more compressed dynamics than their biscuit-bridge cousins. One major upgrade to the new instruments was an adjustable truss rod that counteracts the neck’s tendency to bow under string tension.

My mandolin, built in 1975, was one of the first reissues. The model was known as the Ampliphonic, but it was changed to the original Model 15 designation by 1978. Mine has minor wear but is in excellent condition overall; the neck has been reset and some minor work done to alleviate a kick-up in the fretboard over the body, but otherwise it’s all original. Dobro continued to build mandolins until 1995, shortly after OMI was acquired by Gibson. The newer mandolins fetch a considerably lower price than the originals, but given the improvements in sound and playability, I’m happy with the one I have. It’s one of my favorite instruments, and people who hear it are often amazed both by its unique appearance and the warm torrent of sound that emanates from its small body.