Plugged In

Temporarily moving my home recording studio, I found myself sorting through a mass of tangled cables and leads, some of which I have owned for more than 30 years. This started me thinking again about connectors, of which there are a huge variety, some of which persist and others have a much shorter vogue. But in one way another they all contribute to the story of the machine age (or ages), of the development of technology, mass production and most obviously the role of standardisation. In fact I would hazzard that the connector or plug is an archetype of mechanical reproduction; connectors imply a set of standards, that A fits with B, and often they serve to bridge between one standard and another, they are adaptors. Ever since Samuel Colt displayed his revolvers at the Great Exhibition of 1851, the progress of a technological society has depended on the interchangeability of parts, and at times, in a Capitalist society, prolonged battles between competing standards.

In this post I want to explore the histories of some of my collection of connectors, but given the amount of time it takes to find out anything about them, I’m going to develop this progressively by plugging in items as I gather information. I begin with what may be the oldest standard plug still in use; the ¼ inch TRS jack plug (sometimes called a phone plug in the US).

Jack Plug

What is it? Most people will be most familiar with its more recent 3.5mm variant that is the almost ubiquitous connector for headphones and the like on iPods, laptops etc. The 3.5mm plug is a true TRS in that it has 3 points of connection; tip, ring and sleeve. On your iPod this carried the stereo signal on tip and ring with the sleeve being common to both. But straight away we need to note that there are jack plugs that have only tip and sleeve, such as the standard used for electric guitars and other musical instruments. The jack is almost always used as an audio connector, although on occasion they are deployed to carry control signals; foot switches and pedals for guitars and amplifiers and as patch cables on modular synthesisers, for example.

The etymology of jack is not at all clear, the most popular account being that early variants resembled a jack knife, which is to a certain extent true (see Figure 3). As with every invention, the origin of the plug is shrouded in the mysteries of claim and counter claim, because like most standards it emerges from a cloud of uncertainty. What is certain is that its origin lies in telegraphy and the transition to telephony in the United States in the 1870s and 80sHere it should be noted that when telephony crossed the Atlantic, and eventually became, in the UK, the remit of the General Post Office, a different standard of plug was adopted; the Post Office Jack or PO jack. This has the same basic form, with tip ring and sleeve, but different dimensions. During my sojourn with the BBC (see Dreaming of BH) the PO jack was the standard, as it was at one time in recording studios, and in the Control Room where I worked there were bays and bays of 19inch racks with endless rows of PO jack sockets, some of which had had the same leads connected to them for years.

The first thing to bear in mind with the origin of the jack plug is that early telephones, like telegraph before them, used a single wire to carry the signal, the circuit or return being completed by an earth connection. The earliest plugs, then, had to connect a single wire. Whilst this system had been entirely adequate for the essentially digital telegraph signal, it soon proved inadequate for sound and in 1879 Alexander Graham Bell patented a two wire twisted pair cable which became the standard for telephony. The jack plug has its origins in switchboards, the most simple of which were pegboards or button switches, used in telegraph stations to connect local apparatus to the (single) line (Figure 1). The plugs or pegs were simple brass rods with a handle, inserted into a shaped slot between two contacts. The first telephone exchange is attributed to the Hungarian engineer Tivadar Puskás, then (1877) working for Edison. A year later the first public exchange was built by George W. Hoy in New Haven, Connecticut (appropriate location), apparently a rather Heath Robinson affair constructed from odds and ends (Figure 2).

However this was soon refined with the aid of a Mr. Snell, whose switchboard “jacks” do hint at the knife origin for the term. But here it seems, from the illustrations, that connections were made by turning the jack such that the “knife guard” element connected the two adjacent terminals (Figure 3). Around the same time one George F. Durand of St. Louis used what was described as a “jump jack switchboard,” but perhaps most significantly Thomas B. Doolittle of Boston also developed a switchboard which appears to have used plugs and cables to make the connections (Figure 4). Here the cables were counterweighted to draw them back into the board to avoid tangles – a feature evident on many later manual switchboards.

Finally, in 1881, Western Electric (originally part of Western Union but now owned by Bell) developed its “Standard” switchboard, which appears to be the prototype of all subsequent types, using the plug and cord method (Figure 5). This type may or may not be the “Gilliland” switchboard illustrated in Popular Science Monthly (Figure 6), Ezra Gilliland being an “inventor” and colleague of Thomas Edison. Although several other plug boards are cited as the origins of the jack plug, e.g. that of Milo G. Kellogg (1888) and Charles E. Scribner (1884), both appear to be intended for use with a single wire, at a time when Bell had already introduced the use of a twisted pair of wires. Illustrations from the 1908 Western Electric catalog (Figure 7) indicate that at this stage the jack had only a tip and sleeve, I imagine that the ring was only introduced when circuits were either balanced (Note 1) or carried a stereo signal.

From this point, the jack then became a standard which other technologies could appropriate. Thus Beachamp’s 1934 patent for the “frying pan” guitar (Figure 8), the first truly electric guitar, includes a “mono” (i.e. tip and sleeve) double ended jack lead to connect the instrument to an amplifier.

I have not thus far tracked the details of the use of the 3.5mm TRS jack; earphone jacks were common on early transistor radios of the late 50s and early 60s. One obvious candidate for the emergence of this standard would be the Sony TPS-L2 Walkman introduced in 1979 (Japan) and 1980 (USA) which had 2 such mini jack sockets to allow shared listening (Figure 9, de Gay et al 1997).

Forthcoming: DIN Plug, SCART and MOLEX

Notes

(1) A balanced cable uses tip and ring for the signal and sleeve for an electromagnetic screen. Usually the terminals are balanced by connection to a 1:1 transformer or “rep coil” which eliminated interference induced in the cable.

Sources

Deland, Fred 1907 Notes on the development of telephone service. Popular Science Monthly. March pp229-

du Gay, Paul et al 1997 Doing Cultural Studies: The Story of the Sony Walkman. Milton Keynes: Open University.