Sola Sound released the Tone Bender MKIV, approximately during the year of 1970, during which the model was regularly advertised in Beat Instrumental & Melody Maker publications. At the time, the only thing that set the MKIV apart from the Tone Bender MKIII that they were already producing for Vox, was the fact that the MKIV came in a slightly different enclosure, and was printed with different graphics. The Tone Bender MKIV was also a three-transistor, three-knob fuzz box, with a circuit that was based on the Baldwin-Burns Buzzaround.
By approximately 1971 (according to date codes on surviving examples), Sola Sound had redesigned the artwork on this model and begun production of one of the most recognisable versions of all of the Tone Benders. Initially, the circuitry was unchanged, but the model designation of the Tone Bender MKIV was removed, and the pedal was once again, known simply as the ‘Sola Sound Tone Bender’.
Early examples were designed in a yellow colour scheme, but Sola Sound soon settled on a grey design, and this was how the Tone Bender would appear until the late-1970s.
In the same way that Sola Sound were manufacturing their Tone Benders [MK1.5, Professional MKII & MKIII] under different names throughout the mid-to-late 1960s, the MKIV was also supplied to various different companies during the 1970s.
The circuits & enclosures that Sola Sound were using in the early-to-mid 1970s for their own ‘Sola Sound Tone Bender’ were identical to the ones built for companies like Carlsbro and Park. (Photo credit: S. Fujita)
The MKIV gradually evolved over the course of production, and this is reflected by the change in the electronic parts that were used. The same model that started out with a fuzz circuit based on the Baldwin-Burns Buzzaround was later being built with a silicon-transistor fuzz circuit, loosely based on the Electro Harmonix Big Muff Pi. The Tone Bender MKIV was finally discontinued in the late 1970s.