Essex A-15

Based on the Vox® AC-15


(it has only volume and 1 tone control, no presence, no master)

Designed by D Denney for Tom Jennings’s JMI company in 1957 and often lauded as “the first tube amplifier specifically designed for the electric guitar,” the AC-15 has been hailed as one of the juiciest distortion generators ever created, and sought after as a top-flight tone machine for five decades. With one channel utilizing an EF86 pentode preamp tube, a second utilizing an ECC83 (12AX7), luscious tremolo, and a pair of EL84s in hot cathode bias with no negative feedback(aka “class A”), it emits an extremely complex, harmonically-saturated distortion tone when driven hard, and classic British jangle and chime when reined in. The bloom, depth and dimension of this combo is further enhanced by its legendary speaker, the alnico Celestion Blue (G12 T530). An EZ81 tube rectifier contributes to its stunning touch sensitivity. Quite simply, this is one of the most copied amps in history, the inspiration to countless boutique designs, and truly a tone to die for.

There was no master volume on the original circuit, and there is only one preamp stage before the signal hits the power amp. Normally, we put the master volume right before the power amp, but if we did this then we have the Drive knob and the Master Volume knob in pretty much the same place in the modeled amp circuit.

So, for the AC-15, the master volume is post-phase-inverter in the full amp model. This allow the user to use the Drive knob to hit just the Phase Inverter tubes harder. However, in this amp the power tubes can distort a LOT. When this is combined with the fact that the preamp doesn’t distort a whole lot on its own, it can produce a situation where turning the preamp up and the master volume down will clean up the sound quite a bit. The preamp barely distorts and the power amp distorts a TON. This is the opposite of many amps where the preamp is designed to distort and, while the power amp can distort as well, most of the crunch comes from smashing the preamp.

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