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Vox Amplification

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Submitted By ajrios87
Words 1033
Pages 5
Anthony Rios
2/27/12
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Vox Amplification: A History
The Vox Amplifier Company are makers of guitar amplifiers that boast a history in rock and roll music, and with the invention of the electric guitar musicians were not only amplifying there guitar but exploring new frontiers.
The Vox Empire and JMI (Jennings Musical Instruments) started with just two men by the names of Thomas Jennings and Dick Denney. Thomas Jennings was always interested radios and electronics as well as an amateur accordion player from there he took his interests and joined the British Army, where he was a part of the Royal Electrical and Mechanical Engineers. Sometime in 1942 he received a medical discharge and took a job at a munitions plant in Dartford Kent, England. While working at the plant he met a big band guitarist and fellow musician Dick Denny. Denney, who was also interested in electronics and radio technology, would befriend Jennings and the two would on occasion play together during air raids to keep the morale up.
With the war still waging on in 1944 Jennings and Denney would go their separate ways and Jennings would start a small part time business selling second hand instruments and doing repairs. Around this time his business was growing fast and so was he needs to find a bigger commercial venue. It was 1946, the year after the war ended, is where he would open his first commercial premise mainly importing accordions and other musical instruments but also inventing new products. Jennings first successful production was the Univox Electric organ. This invention would serve as a launch pad for one of the most successful instrument manufacturers.
It was the mid 1950s and a new type of music was making its way across the Atlantic from the United States just simply called rock and roll. With the popular growth of rock and roll and the influence it was having over England’s youth that JMI would take notice and start designing guitar amplifiers. These amps would all be built in-house and were marketed but enjoyed very little success. All the while Denney was designing and experimenting with amplifying the guitar and developed a 15 watt amplifier that would feature a 12 inch speaker. In 1957 Jennings was looking outside the company for amplifier designs and he had heard of Dick’s amp and invited him to factory. Denney brings along the prototypes he designed, Jennings liking what he hears and offers Denney a job at JMI. Denney accepts the job and joins the JMI team as an amp designer and JMI would now become Jennings Musical Industries.
VOX AMPS in the 60s
The first amp that was branded with the VOX name was the AC/2 practice amp that came out in 1958 but it would soon be named the AC/4 for its actual power output in 1961. Cosmetically the AC/4 was designed with the “TV front” look as well as covered with fawn vinyl and the classic brown diamond grill cloth. Electronically its circuitry contained 4 tubes: one EZ80 rectifier, one EL84 power tube, one ECC81 (aka 12AX7) and one EF86. This amp would be one of many to join a complete amplifier line.
AC-15
The AC-15 was the amp that really started it all. It came in two different models, the first in 1958 featuring the TV front design and then in 1961 featuring the Fender style cabinet. First designed by Dick Denney in 1957 and then produced in 1958. It had the same cosmetic features as the AC 4 but it was electronically how it was different. The tone produced by the AC-15 was the sonic blueprint for all JMI tube amps. Denney’s design held three key ingredients for the VOX tone. The power section of the amp consisted of two EL-84 power tubes to make the first component in the VOX tone along with the EF-86 preamp tube. However, the EL-84 tube had a downside. The tube had a tendency to distort when driving the amp too hard because of reduced headroom. Denney also had this covered he incorporated the negative feedback circuit to clean up the distortion but when introducing this circuit it also took some of the harmonics out of the tubes. After some tests Denney decided he liked the way the amp sounded without the negative feedback circuit. The second ingredient of the VOX tone would be to remove the negative feedback circuit from the power section in all JMI tube amps. The final ingredient involved how to bias the output tubes. Denney realized that the AC 15 would be a better sounding amplifier by abandoning manually biasing the tubes but favoring self-biasing.
AC-30: The Crown Jewel
The AC 30 is one of the most coveted amps on the market today and over the years it has been produced in several models. The first was the AC-30/4 to be designed for British bands endorsed by VOX in 1960. Rock and roll was becoming more and more popular in Britain and the need for a more powerful amp was evident. The power amp section contained a quartet of EL-84 power tubes, but in the preamp section was the EF-86 tube. The EF-86 is a high gain tube that would the drive the AC-30/4 into a harmonically rich distortion when pushed. However, due to the vibrations of the amp when being played loud the EF-86 would fail and have to be replaced all the time. Over time the cost of the tube would to be too high and the engineers at VOX would soon design a new amp without the EF-86.
The AC-30/6 would be born into the VOX line. This amp was influenced by the introduction of the Fender Twin 60-watt amp to the UK. VOX decided to resolve this by developing the AC-30/6 which would feature an additional speaker and doubling of the output power tubes. With the AC-30/4 it also included the EF-86 tube but VOX replaced this tube with a battery of ECC83 (12AX7) tubes.

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