The Evolution of Moog Theremins, 1957-1964

R. A. Moog (1957 – 1964)

As the latter part of the 1950s arrived, Bob’s theremins continued to evolve, with the new offerings following two distinctly different directions. Model numbers were replaced by names, following the growing trend in other markets. Thus, just as the Chevrolet 210 was renamed Biscayne, the R. A. Moog Company’s 305 and 351 were superseded by Vanguard and Professional, respectively. Once again, Bob offered two price options, and as before, timbre control was available only on the higher priced Professional model. Perhaps more significant from a technological point of view however, was that while Vanguard retained vacuum tubes for the time being, the Professional was the first of Bob’s instruments to embrace the latest transistorized “solid state” technology.

As the vacuum tube era waned, Vanguard would ultimately follow in Professional’s progressive, solid-state footsteps in its second incarnation as "Vanguard II” in 1964. In an apparent effort to standardize model names, Professional became “Professional II” around the same time. The newly minted Professional model, in addition to retaining transistors, would likely also have benefitted from Bob’s ever-evolving circuit ideas and refinements.

Of the two, Vanguard was more functionally streamlined, with its single, non-selectable timbre, or “tone color” engineered to be harmonically pleasing. In this way, it may be thought of as the logical successor to Model 305. Likewise, Vanguard had a minimal number of controls, set within the lower part of its ultra-modern, wedge-shaped cabinet. The performer had at their fingertips only two rotary control knobs and one three-position switch (Off/Silent/Play). The middle position was to keep the tubes warm and ready for action during silent periods.

From an internal point of view, Vanguard was simplified by employing AC/DC vacuum tubes wired in a “series string” arrangement, thus eliminating the bulky power transformer. This not only represented a substantial parts cost savings, but it also made the instrument lighter, an indication that Bob was already listening to musicians’ feedback and taking their suggestions to heart. Unlike the Models 305 and 351 which required a separate amplifier, Vanguard reverted to Bob’s first offering, the Model 201 by incorporating a built-in amplifier and speaker, all “housed in a handsome, hand-rubbed solid mahogany cabinet”. The pitch range of Vanguard was stated to be “three and a one-half octaves, extending from an octave below middle C to two and one-half octaves above middle C”.

At the high end, in addition to having transistors and a built-in amplifier with a larger speaker, the Professional model benefitted from the tonal groundwork laid by Model 351, in the form of a four-position timbre control, carrying over switch positions Principal, Horn, Woodwind and String. Gone were the dedicated overtone options of the pioneering models 201 and 351, as Bob had discovered that not every combination of overtone and timbre was pleasing. It is also likely that while Bob may have taken delight in the 351’s sheer number of controls and switch positions, he may also have discovered it to be daunting to the typical end-user.

As with Model 351, the tone colors were stated to be an approximation of the representative timbres. Thus, “The Principle tone is mellow and ethereal, like a flute. The horn tone is sharp and nasal, like that of an oboe. The Woodwind tone is hollow and woody, like a clarinet. The string tone is rich in overtones, like any stringed instrument.” As for the Professional’s pitch range, “The Principle and Horn tones encompass a range of from one-half octave below middle C to three octaves above middle C. [While] the pitch range of the Woodwind and String tones extend from one and one-half octaves below middle C to two octaves above middle C. Thus, the total pitch range of the Professional model is four and one-half octaves”.

In an inspired departure from the Vanguard’s trendy wedge shape, the cabinet of the Professional reflected, and likely was a heartfelt homage, to the RCA Theremin which it resembles in general shape and proportion.

Marketing The Vanguard and The Professional


Continuing in the entrepreneurial spirit, Bob broadened his accessory offerings to include a sturdy but aesthetically pleasing instrument stand, and a wooden carrying case with corner protectors and a cloth instrument cover, which he depicted in sales literature covering the carrying case, with the suggestion that this would also make an attractive stand. Additionally, a choice of cabinet woods could be ordered, as well as theremins made to order, meeting “virtually any special requirement”.

Although an original, late 1950s R. A. Moog Company brochure depicts only the Vanguard and Professional theremins, along with the stand and carrying case, a glimpse of the shape of things to come can be found in the small print under the heading “Custom Made Theremins”: “An example of special Theremin design is a completely transistorized, battery operated, portable Theremin. This entire instrument weighs only eighteen pounds, but has the same range and playing characteristics of the standard models”. One has to wonder whether this new battery-powered theremin was the brainchild of Bob’s prolific imagination, or the suggestion of a performing musician, to whom even greater portability and convenience would have been an added benefit.

Although both the Vanguard and Professional model theremins are identified only by their respective names in period brochures, the Vanguard is identified as “Model 505” and the Professional as “Model 551” in the R. A. Moog Company dealer price lists. In the September 1959 price sheet, Model 505 shows a list price of $313.50, while Model 551 is priced at an impressive $632.50, with discounts to dealers. In 1960, the list prices had risen to $395 and $650, setting the stage for the soon to be more successful transistorized Melodia, a bargain at $75.00 or a mere $29 in kit form, sans cabinet enclosure.

As with the Model 201’s debut in an article written by Bob for Radio and Television News magazine in 1954, a theremin design very similar to what would become the Melodia was first introduced in the January 1961 edition of Electronics World, the new name for Radio News. In an article titled “A Transistorized Theremin” which intended to teach readers to build a “self-powered, three octave instrument,” Bob takes the readers through building the theremin. In This article, Bob provided a more detailed description of how to wind the coils, learning from shortcomings of his previous article’s oversights. The end of the article gives a short list of exercises to practice, which also appeared more expanded in the instructions of Bob’s later theremins, like in the Series 91 instruction manual.

After a few small modifications to the design, the theremin was sold under the name Melodia as a kit version or a completed ready-to-play instrument. The kit version came with a reprint of the article and an assembly manual with a checklist for each step in the construction. The components in the kit were premium quality, and the chassis and front panel were pre-punched, formed and silkscreened. Over the span of the Melodia production the R. A. Moog logo would change from the design with staff lines and a vacuum tube, to the more familiar stylized musical note in the ‘o’ of Moog.

The Melodia is unique in the oeuvre of Bob’s theremins with regard to its power supply. The new instrument’s more efficient, transistorized design enabled it to be powered by a single 6 volt battery, as called for in the original instructions. Most Melodias still in use today have been modified to accommodate more readily obtainable AA or 9 volt batteries.

Following in suit with previous releases, Bob designed a professional model with timbre options offered alongside the Melodia. The Troubador is powered by a 115 volt, AC power supply instead of a battery and it features the addition of a continuously adjustable timbre control, abandoning the discrete, instrument-labeled switching options of the previous 201, 351 and Professional model theremins.

Internally, the Troubadour, it differs in appearance from the Melodia in a few ways. The most prominent difference is the use of components mounted to prototyping perfboards, still employing point to point wiring, and mounting the boards vertically to make room for the power supply and the additional timbre control circuits.

The Troubador theremin is quite rare. In a letter enclosed with a Troubador returned to the owner after repair in 1993, Bob Humbly wrote, “This theremin does have some value now. Literally dozens of people have called within the past year looking for one of these.”