Tom Jennings, the president of JMI Vox, resented having to pay the dollar per amp licensing fee charged by Hammond. Most manufacturers were content to license the Hammond patent. Hammond required that a manufacturer pay a one dollar licensing fee for each unit produced using the Type 4 reverb system. Fender was incorporating the Hammond Type 4 reverb system into their Princeton Reverb, Deluxe Reverb and Twin Reverb amplifiers, among others. Hammond Organ had developed their "Type 4" reverb tank several years earlier and was licensing the technology to guitar amp manufacturers. ![]() When these changes in resistance were applied to the preamp signal, tremolo was created.Įlectronically simulated "spring" reverb was commonly available in guitar amplifiers by 1966. The flashing lamp in the opto-isolator caused the resistance of the LDR to vary over a wide range. Advancing the Depth control increased the brightness of the flashes. Advancing the Speed control increased the speed of the flashes. The tremolo drive circuit caused the lamp to flash inside the opto isolator. The tremolo drive circuit was located on the left rear tag strip (see rear chassis photo above). When dark, an LDR has electrical high resistance, but in the presence of light, the resistance of the LDR drops to nearly zero. The opto-isolator was comprised of a small light bulb and a light dependent resistor (LDR) in a sealed can (see photo at right). The 760 tremolo circuit utilized an opto-isolator. The "Vibrato" channel of the Vox 760 offered tremolo, not vibrato. Vibrato is frequency modulation while tremolo is amplitude modulation. Many amp manufacturers used the term "vibrato" to describe an effect more correctly known as tremolo. Thomas was now influencing the designs of amps made by JMI. Introduced by JMI in 1966, the 760 had a fully featured modular solid state preamp circuit. Thomas Organ made a compelling case to their UK partners for the advantages of modular solid state amp des ign. Transistor circuits cost less to build and could be more dependable than their tube counterparts. ![]() Denney witnessed how transistorization allowed Thomas to add a plethora of features to their solid state preamps. JMI Vox lead engineer Dick Denney traveled from the UK to California in October 1965 to get a first hand look at the progress made toward the conversion from tube to solid state amp circuitry at Thomas. The new Vox amps built by Thomas Organ would be transistorized. As a first priority, Thomas Organ wanted to eliminate tubes from their amps. The solid state preamp circuit from the Vox 760 was also shared with the Vox 715, 7.Ī newly signed distribution contract finalized in the summer of 1965 between JMI and Thomas Organ allowed Thomas to design and produce their own Vox products for the North American market.
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