Classic Gear: The 1965 Vox AC30 "Top Boost" Combo - GuitarPlayer.com

Classic Gear: The 1965 Vox AC30 "Top Boost" Combo

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From popular reissue to favorite boutique-amp inspiration to pride of place on every modeling amp’s selection menu, the mid- ’60s Vox AC30 with Top Boost is one of the most copied, emulated, and reproduced amp designs ever created. Hell, if imitation is the sincerest form of flattery, the AC30 has been red-cheeked for decades. This legendary British tube amp first proved itself on U.S. shores when the Beatles took on America in 1964, and was a mainstay of the British Invasion that followed. From that point on it remained an unshakeable classic. After the virtual who’s who of stars who played through an AC30 throughout the ’60s, it raged on into ’70s in the backlines of Rory Gallagher, Brian May, Tom Petty, and Mike Campbell; reestablished its street cred with The Edge and Peter Buck in the ’80s; helped Brit-pop roar back alongside Noel Gallagher in the ’90s; and blasted through into the new Millennium with Dave Grohl and countless others. Whether you keep it clean for jangle and chime à la Buck’s R.E.M. tones and seminal Campbell/Petty, or crank it for sweet, searing, harmonically saturated overdrive like Brian May, the AC30 has proved itself time and again a first-call, do-it-all foundation of stellar tone.

Organ maker Tom Jennings founded Jennings Musical Instruments (JMI) in 1957 to cash in on the rock-and-roll boom, and birthed his Vox brand to do the job. The AC30 evolved from Vox’s debut amp of 1957, the AC15, which has often been describe as the first amplifier designed specifically for the guitar (rather then being cobbled together from standard amplifier circuits supplied by the tube manufacturers). JMI designer Dick Denney approached the job with the guitar’s own sonic performance in mind, and the results speak for themselves. As rock raged through the late ’50s, though, a more powerful amp was needed. In late 1959, Denney and Jennings first tried using two more powerful EL34 tubes in a short-lived AC30, then simply doubled the AC15’s output stage to four EL84s to give birth to the amp we know and love today.

The AC30’s cathode biasing and lack of negative feedback give plenty of sparkling, slightly unchained chime to the guitar’s upper-mids and highs, thanks to the way they encourage second-order harmonics as artifacts of distortion. This offers a flattering tonality at low and middle volume levels, and a creamy, textured overdrive when cranked. Also, in using an output stage with no negative feedback loop to dampen and tighten the response, Denney’s design offered a rich, touch-sensitive, and very playable performance when pushed—a feature further enhanced by the amp’s tube rectifier. While both the AC15 and AC30 are often sited as being “classic class-A amps,” it is probably more accurate to sum up their sound as the result of these features: cathode biasing, lack of negative feedback, tube rectifier, and easily overdriven EL84 output tubes.

Early AC30s sound great in their own right, but the model evolved to its optimum form when the Top Boost tone stage was adopted—first as a back-to-factory add on in 1961, then as a standard model option in 1964. The Top Boost circuit adds another preamp tube to the signal chain, as well as a simple yet powerful EQ stage with Treble and Bass controls that are very active and interactive in use, upping the chime factor and adding a little grind when pushed hard. With all of these elements under the hood, the AC30 combo is topped off by a pair of delectable Celestion G12 speakers with alnico magnets, which translate everything from the amp’s sweet sparkle to its raw, singing lead tones as if they were born to do the job. Put it all together, and it’s a sound that has launched a thousand hits!

ESSENTIAL INGREDIENTS

• Four EL84 output tubes generating more than 30 watts RMS,
• Cathode-biased output stage with no negative feedback
• ECC83 (aka 12AX7) preamp tubes
• Cathode-follower “Top Boost” tone stage
• Two Celestion G12 speakers with alnico magnets
• Open-back combo cab made from Baltic birch plywood

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