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 that the model was printed with different graphics.

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.

Tone Bender MKIV, “bendy” logo

The earliest versions of the Tone Bender MKIV were formally branded as ‘Sola Sound Tone Bender Mark IV’ pedals, and were housed in grey, pressed steel enclosures. To help to differentiate these early Tone Bender MKIV pedals from later examples, collectors have in recent years began informally referring to them as having “bendy” or “spaghetti” graphics (referring to the way that the ‘Tone Bender’ lettering has been stylised).

Slightly later examples featured the same graphic design, but came in both yellow and in orange colour schemes instead. The Tone Benders in these yellow and orange enclosures disproportionately resurface in central Europe, despite having been built in Britain. This is indicative of Sola Sound’s distribution model at the time. (Photo credit: S. Castledine, W. Merkel & eBay.com)

Tone Bender MKIV, “Batman” logo

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. The model designation of the Tone Bender MKIV was removed, and Sola Sound’s fuzz box was once again, known simply as the ‘Sola Sound Tone Bender’. Internally, however, the circuits of these newer pedals remained unchanged.

Collectors in recent times have begun informally describing this version of the Tone Bender MKIV as being the version with the “Batman” logo, referring to the cartoonish stylisation of the ‘FUZZ‘ logo. Early pedals with this design scheme were printed with red & black ink, onto yellow enclosures. Sola Sound soon settled on a grey colour scheme, and this was how the Tone Bender would appear until the late 1970s.

Tech specs

The Tone Bender MKIV gradually evolved over the course of production, and this is reflected by the change in the electronic parts that were used, and in the overall construction of the circuits. The images above demonstrate the changes in the MKIV’s circuitry over the course of the 1970s. (Photo credit: S. Castledine & Crave Guitars)

MKIV’s built during the first half of the 1970s featured a three-transistor circuit that was loosely based on the Baldwin-Burns Buzzaround. By the late 1970s, the grey Tone Benders with the “Batman” logo were being built with a silicon-transistor fuzz circuit, loosely based on the Electro Harmonix Big Muff Pi. Sola Sound’s development of the circuits inside Tone Bender MKIV pedals is mirrored by the development of the same circuits in the Tone Bender MKIII, which still being supplied to Vox, in parallel with these pedals.

The Tone Bender MKIV was finally discontinued in the late 1970s.

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    6 thoughts on “Sola Sound Tone Bender MKIV

    1. I had the version with the “Hit It’ arrow on it. I’m sure mine was the orange colour though, maybe they experimented a bit, or my memory is deceiving me.
      I can’t remember what I paid for it, bought about 1971 I think, sold in 1976 to help with house buying fees – for £10! I know, I still cry about it.

    2. I still have the Carlsboro version of the Tonebender. I bought it at the same time as I collected my lefty CSL Les Paul copy in September 1973. Very exciting day. It still works perfectly. From memory it was £14. The only replacements have been the battery connector and, courtesy of Ant Macari just a year ago, one of the control knobs. The rubber feet wore away and I’ve not been able to find replacements.

      I may have a small party for it in about a year’s time on it’s 50th birthday!

      1. No idea, I’m afraid. The vast majority of these pedals were built with unlabelled transistors (possibly made by STC). Every now and then, we do see some unusual transistors, e.g. I had a mid-70s Carlsbro fuzz at some point, where one of the transistors was labelled as an OC71, and I’ve seen an unusual transistor in another (earlier) MKIV that was actually branded by STC. Some of the earliest Tone Bender MKIII’s (with the same basic circuit) came with a variety of black glass Mullard, NKT and TI transistors, but there’s nothing conclusive yet about the MKIV’s, unfortunately.

    3. I have a very early Tone Bender in grey exactly the same as in the opening picture on here. However, when I remove the back, the circuit board is differend. The 3 pots are not visible but have solder tags coming through the pcb. Is it possible that this is a previous model to the MK IV that shows the pot shaft going through the pcb?

      1. I suppose I really need to tidy this page up with some more detailed pictures of the various MKIV models!

        The printed circuit boards that were mounted with the track side facing outwards, as in your pedal, are how Sola Sound built the earliest of their three-knob Tone Benders (MKIII & MKIV). It’s a fairly common feature in the Vox-branded Tone Bender MKIII, which was introduced earlier than the MKIV model (but, confusingly, continued to be built in parallel with the MKIV, during the 1970s).

        The Tone Benders in the grey cases, with the ‘wiggly’ logo (like yours), are the first of the MKIV type, and so they tend to come with that ‘reversed’ PCB as well, but the construction changed by c. 1972. The circuit is pretty much identical to the more often seen MKIV’s, with the components facing outwards — the main difference being that Sola Sound moved over to using Radiohm pots, in place of the (likely) Erie pots in your pedal.

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