Friday 12 October 2012

History of the VOX AC30

One of the finest Guitar amps is the VOX AC30  Used by bands like the Beatles and lots of other famous bands so here is some history
 

Vox AC30


 




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. First introduced in 1958 due to the growing demand for higher-wattage amplifiers, it became an iconic amplifier for British musicians and soon for others.

 

 

 History

The Vox AC30 was originally introduced in 1958 as “big brother” for the fifteen watt (15 W) 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 in a "TV Front" cabinet as opposed to the later, conventional twin 12” speaker configuration. The AC30/4 sported two channels with two inputs – hence the “4” in the model name, and had a single tone control in it as well. The amplifier also had a GZ34 tube rectifier,  and the power amplifier circuit had EL34 tubes. The preamplifier also carried over the EF86 pentode in its "Normal" channel which, coupled with the AC30's increased output over the AC-15, exposed a reliability issue. The high gain EF86 tube was susceptible to microphonics, or even failure, when exposed to the increased vibration present in this uprated amp.
This first generation of AC30s were housed in "TV-front" cabinets, much like the early to mid 50s 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 60s 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 an ECC83 (12AX7) for the EF86 tube. Its circuit had three channels, each with two inputs, and was therefore named AC30/6.
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 earlier 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. Later on, Vox also offered additional versions of the AC30 unit. In addition to the "Normal" version without the Top Boost, and the Top Boost version (which was a Normal version with the "Brilliance" unit added), Vox, with slight circuit modifications, created two more versions that were “voiced” in Brilliant (Treble), and Bass styles.
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 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 1980s, a company in Marlborough, MA, called Primo, imported and began re-distributing the AC30s in the U.S.

AC30 Heritage (2003)

In 2003, Vox created the "AC30 Handwired Limited Edition" amplifier (AC30HW). The amplifier differed from the standard offering in notable ways. First, the circuitry was constructed using old-fashioned tag strips. According to Vox, this was far more labor intensive. But it allowed for easier repair versus circuit boards because there were no traces to burn. According to the Vox showroom site:
"1960's era Vox amps were hand wired on tag strips. The connecting leads (or wires) from each electronic part was manually wrapped around a terminal, or "tag," and then soldered. This mode of amp construction is very labor intensive and the workmanship and accuracy of the employee building the amp will affect the performance of the product. It was for this reason that most electronics manufacturers transitioned to phenolic printed circuit boards by 1970."
The second notable difference was the features and control layout. Guitar Player magazine reviewed the amp in its "Exotica" feature, December 2002. The article specifies details of the amp including price, and its control layout:
"The AC30 HW ($4000; head $3250; 2X12 cab $1350)--which was developed with input from boutique amp desgner Tony Bruno--features the famous Top Boost preamp, but has a control that is quite different from the standard model. For staters, there are only two inputs, which are marked Hi and Lo (Ac30s have six). To the right are the volume, treble, bass and tone-cut controls, a tremolo section with speed and depth knobs, a reverb section with reverb and tone controls, and a master volume." [And further into the article:] Top of the Marque. The AC30HW is by far the best AC variant to date. Few amps come close to matching its radiant complexity and those that do typically don't offer reverb and tremolo. The only downer about the HW is that only 350 of them will be made (along with 200 heads and cabinets)."

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 (Output Bias switch: "50 Hot": 33W at full power, "82 Warm": 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.

AC30 Handwired (2010)

Introduced in 2010, the amp featured Hand-wired turret board construction (against cheaper PCB construction), Birch-ply cabinets featuring solid bracing and a natural high frequency diffuser (verses MDF cabinets and no high frequency diffuser); All-tube design (different from the Custom series tube pre/power amp but solid-state rectifier); ECC83/12AX7 preamp tubes (x3) EL84 power tube quartet; (AC30 models); EL84 Duet (AC15 models); GZ34 rectifier (AC30 models); EZ81 rectifier (AC15 models); came factory-fitted with matched Ruby Tubes to provide extended dynamic range; maintained the traditional VOX two-channel design (Top Boost and Normal. High and Low inputs for each channel); the Normal channel features an additional BRIGHT switch; The top boost channel features a HOT/COOL switch to achieve even more gain. A Master Volume/BYPASS switch completely bypasses the Master Volume section allowing incredible levels of gain and sustain to be achieved. OP mode switch cut the amp’s Output Power level in half (30 > 15 on the AC30, 15 > 7.5 on the AC15) allowing higher levels of saturation to be achieved at lower volumes). A Vintage fawn-colored vinyl covering, reminiscent of the 1960 classic AC30 and was available with either Celestion Alnico Blue or Celestion G12M Greenback speakers. A VFS1 footswitch controls the Top Boost channel's HOT/COOL switch was also included.

AC30 Custom Series

At the 2010 Winter NAMM expo Vox introduced the Custom series; these models were updates to the 2004 Custom Classic series amplifiers and featured 2 channels (Normal and Top Boost) with 2 inputs for each channel (High and Low), more akin to the original AC30/4 released in 1958. Available with either Greenback speakers (C2) or Alnico Blue Speakers (C2x), and was also available as the AC15. Later limited edition models include the AC30BL, a tygoon blue tolex with grey speaker cloth, an AC30C2RD with a red finish, and the AC30C2 Black Comet; featuring a patterned finish all are identical to the C2.The amp featured an option known as "Jumping" where the High-Normal channel could be linked to the Low-Top Boost channel with a patch lead, whilst the guitar is plugged into the High-Top Boost channel, allowing both channels to sound and create a fuller, thicker overdrive sound. The amp also featured a solid-state rectifier to increase reliability. Controls include a Normal volume, Top Boost Volume, Treble and Bass controls, Reverb Tone and Level controls, Tremolo Speed and Depth controls, a Tone Cut control (to add further control over the higher-frequencies), a Master Volume, and a Standby and Power Switch. A true bypass effects loop, extension cab output and external cab output were also included; as well as an input for the external foot-switch (to control Reverb and Tremolo). The amps are produced in China. The amps were released to be a critical success, garnering awards such as Music Radar's "Guitarist Choice" award.

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. JMI later changed their alnico speakers to ones made by Tayden.

AC30VR

Another recent addition is the VOX AC30VR (Valve Reactor). According to the Vox website, this version of the AC30 includes both "solid-state" and "tube" technology. Originally designed for the Valvetronix modelling amplifiers, the Valve Reactor circuit places a 12AX7 vacuum tube (or “valve”) into the power stage, which is a tube configured to act as a small power amplifier. Too small to be used as an amplifier on its own, the output of this Valve Reactor circuit is fed to a solid state power amp that boosts the output signal.

Electronics

Though widely believed to be a Class-A amplifier, the AC30 is in fact a class AB1 amp with cathode bias. 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. It's the Celestion "Blue" speakers that 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

So now you know what makes the VOX AC30 so special !

 
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