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Vox AC30

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A Vox AC30 behind a Höfner 500/1 bass and a Gretsch Country Gentleman guitar

The Vox AC30 is a guitar amplifier manufactured by Vox and known for its "jangly" high-end sound.

History

The Vox AC30 was originally introduced in 1958 as “big brother” for the fifteen watt AC15 model, Vox's original flagship amplifier. The AC15 was powered by a pair of EL84 tubes, an EF86-driven "Normal" channel and ECC83-driven "Vib-Trem" channel, and rectified by an EZ81. The Original AC30, or AC30/4, had only a single 12 inch Goodmans 60 watt speaker as opposed to the later, conventional twin 12” speaker configuration. AC30/4 sported two channels with two inputs – hence the “4” in the model name. There was only a single tone control in it as well. The power amplifier circuit had EL34 tubes and the preamplifier used an EF86, which was a pretty unreliable tube and could fail due to vibration. The amplifier had a tube rectifier.

This first generation of AC30's were housed in "TV-front" cabinets, much like the early to mid 50's tweed Fender amps. However, the Voxes sported a thin white covering ("Rexine") with a small printed diamond pattern and larger diamond pattern grill cloth. The EL34 powered AC30 was short lived, and was soon powered by a quartet of EL84 (6BQ5) power tubes, making it truly a doubling of the AC15. Vox initially offered a 1X12" version and subsequently introduced the 2X12" AC30 Twin, which solved the volume problem at larger venues. The first AC30 Twins used Goodmans Audiom 60's 15 Watt Speakers, followed by Celestion G12 alnico speakers.

By 1960, Vox had forsaken the more conservative TV-front look for the now legendary cabinet design that has remained largely unchanged since 1960. The new cabinets featured a different covering known as fawn Rexine, which was a sort of beige leathercloth with a subtle printed grain. The front baffle was now divided by a thin gold-toned strip with the upper valence covered in fawn Rexine, and the lower grille covered in brown diamond cloth. Ventilation was provided by three small brass vents on the top of the cabinet, and the TV-front's single suitcase type handle was replaced with three leather straps.

The Edge's original 1964 Vox AC30 on stage. This AC30 has been used to record every U2 album

To cure the unreliability issues Vox introduced another version of AC30 in 1961 that substituted the EF86 with ECC83 (12AX7) tubes. Its circuit had three channels, each with two inputs, and was therefore named AC30/6. The amplifiers were also available in three different “voicing” styles (Normal, Brilliant, and Bass) that were accomplished by slight circuit modifications.

About this time, the "Top Boost" (or "Brilliance") feature was Vox's optional addition of a rear panel-mounted circuit that introduced an extra gain stage and tone controls for bass and treble (as opposed to the single "tone" control of early AC30s). The unit became so popular that its features were soon implemented to newer AC30/6 models, and the controls moved from the rear panel to the control panel. Vox AC30/6 amplifiers from around 1963 had already implemented the top boost, and therefore had 3 tone controls. People began to refer to these amplifiers as AC30TBs.[1]. Around the same time, Vox also introduced Treble and Bass versions of the AC30 without the Top Boost unit. Instead, the circuits of the Treble and Bass versions were slightly modified to emphasize those frequencies.

In the late 60’s Jennings drifted into financial problems and the company experienced various owner changes. Quality control was also inconsistent.

During the Vox brand's early '70s "Dallas Arbiter" period, the tube rectifiers of AC30s were replaced by silicon rectifiers, which became standard on later AC30TB models. In the late 1970s Vox also introduced a solid-state AC30 (AC30SS), which is the AC30 model that was used by Status Quo. A tube AC30TB with spring reverb feature was reintroduced in 1978.

In spite of at least one AC30 production run titled “Limited Edition” (1991), production of the AC30 has practically never ceased: Newer AC30s are reissues of the various top boost AC30/6 (AC30TB) models. AC30s made between 1989 and 1993 also had spring reverb as a standard feature.

The Rose Morris company, who owned the Vox name through the 1980s, sold Vox to Korg in the early 1990s, who then manufactured a superb reissue of the early '60s AC30 Top Boost, correcting previous inconsistencies from the correct style grille cloth to the GZ34 rectifier tube. These AC30 amps were mostly offered in the traditional black Tolex/brown diamond grille configuration, but were also available in limited numbers with purple, red, or tan tolex. These amplifiers, like all AC30s to this point, were manufactured in Great Britain. These were available with a choice of Celestion "Blue" or Greenback speakers. In the mid 1980's, a company in Marlborough, MA, called Primo, imported and began re-distributing the AC30s in the U.S.

AC30 Custom Classic Series

In 2004, Vox introduced a new series of amplifier called the AC30 Custom Classic. It claims to combine attributes of the original AC30 with what Vox sales literature refers to as a "boutique" of features. Specifications of the AC30CC series are two Inputs (Top Boost & Normal), an Input Link Switch for blending channels, a Normal Volume knob, a Brilliance Switch, a Top Boost Volume knob, a Treble knob, an EQ Standard/Custom Switch, Bass and Reverb Controls (Tone, Mix, and a Dwell Switch), Tremolo Speed & Depth knobs, a Tone Cut knob, a Master Volume knob, a Standby and a Power Switch, switchable cathode bias (low-power switch: 33W at full power, 22W at low power), switchable filter values (vintage/modern), and a true bypass effects loop. Newer AC30CC (or “Custom Classic”) reissues (CC1, CC2X CCH head) are produced in China. All AC30CC series amps, although believed to be 30 watts, are in fact 40 watts in power handling.

AC30BM

Recently, Vox released a limited edition version of the amp, the AC30BM, based on the tone of one of the amp's most prominent and consistent endorsers, Brian May of Queen. The amp is limited to only a few hundred examples worldwide, in a 'never-to-be-repeated' run. As the amp is designed to replicate May's tone, there are no controls on the amp except for a single volume control, though a switch enables the user to halve the number of output valves (therefore reducing the output to 15 watts as well as the volume, making it more suitable for home use), and there is a boost function operated from the included footswitch.

JMI returns

As of 2006, a company having licensed the name JMI (Jennings Musical Instruments) began manufacturing period correct, British made AC30 "copy" amplifiers, available in both black and beige. Since this incarnation of JMI has never owned the Vox brand, their official website lists the disclaimer "JMI amplification are in no way affiliated with Vox amplification (Korg)", and the models are listed as 30/6 (6 input) and 30/4 (4 inputs, sans "Brilliant" channel). As originally the case in the 1960s, Top Boost is offered as a retrofit upgrade and is not standard, and the original configuration 4/6 inputs are offered, with options for Green/Blue speakers, the blue speakers being similar in appearance to the Celestion alnico speaker but made by Fane with fiberglass voice coils which allow them a much higher 100 watt power rating.

Other AC30 Clones

Other popular AC30 clones include: Majic Amplification, Hayseed & JMJ. They have various combinations of the EF86, Top Boost and Normal channel circuits. Recently, the company Bugera has released a clone of the AC30, the Bugera BC30. However, it is also similar to the Matchless DC30(which, in itself started as a clone of the AC30).

Electronics

Though widely believed to be a Class-A amplifier, the AC30 is in fact a class AB1 amp with cathode bias[2][3][4]. It utilizes a quartet of EL-84 output tubes. The high bias condition is believed by some to be the source of the amplifier's famous immediate response and "jangly" high-end, though the lack of negative feedback, minimal preamp circuit, simple low loss tone stack, and the use of cathode biasing on the output stage play at least as large a role, if not larger. Its Celestion "Blue" speakers are integral to the AC30, and also contribute much to the sound of the unit. The two 12" 15-watt speakers, often overdriven and at the brink of their power handling capability, provide a cutting mid-range speaker sound that is immediate and sharp and a distinction from the Marshall or Fender-style amplifier.

Notable users of the AC30

References

  1. ^ Glen Lambert. "Vox AC30 Topboost - Reasons & Origins A?".
  2. ^ Randall Aiken. "Is the Vox AC-30 Really Class A?". Aiken Amps technical pages.
  3. ^ Randy Jamz. "Vox AC30 Myths". Tales from the Tone Lounge.
  4. ^ Mark Breecher & Shane Dolman. "Class Distinction". Sheldon Amps Website.
  5. ^ http://www.greenplastic.com/coldstorage/gear/jonny.php
  6. ^ http://www.greenplastic.com/coldstorage/gear/thom.php
  7. ^ http://www.greenplastic.com/coldstorage/gear/ed.php
  8. ^ http://www.petecornish.co.uk/jptt.html
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