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Jack Plugs – The Gold, the Brass and the Cheap

by Phil Taylor

This article takes a look at its history, development and construction of the ¼” jack plug used for guitars and musical instruments. It also examines which factors and materials utilised in the construction affect its tone quality and durability.

Invention

Original patent drawing for the 'jack' plug connector

Original patent drawing for the ‘jack’ plug connector

There are many aspects of audio and guitar gear that owe their inheritance to the legacy of the telephone industry. One well-known example is the 600Ω impedance of the balanced inputs and outputs found on pro-audio equipment. Another is the common jack plug. It’s difficult to be certain of when the jack plug made its first appearance, however it’s estimated to have been sometime in the late 19th century. There was a patent filing back in 1895 for a “plug and spring jack for telephone boards” that closely resembles a 1/4″ TRS (Tip, Ring, Sleeve) jack plug. The patent also explains how “The invention is applied particularly to a ‘triple plug’ and a corresponding ‘three part spring jack,’”. Additionally, an Electrical Review article from 1903 explains that triple contact plugs were used for telephone jacks during this period. Further information can be found ”International Library of Technology: …Principles of Telephony…” International Textbook Company, Scranton, PA; published in 1907.

Brass Jack Plugs

Brass jack plug with bakelite body

Brass jack plug with bakelite body

These early jack plugs were constructed from brass (an alloy of 70% copper and 30% zinc) with hardened rubber insulators and a Bakelite body. Brass was used rather than copper because it is harder and tougher than pure copper and hence more resilient to wear. However, both brass and copper are prone to oxidation and corrosion as the metal reacts with salts and acids. This isn’t necessarily a problem in the short-term in a benevolent environment. That is, if the jack plug isn’t used in a damp atmosphere or exposed to corrosive substances, then the simple act of inserting and removing it from its socket will remove any small build-up of dirt and oxidation, keeping the contact clean and reliable.

In more adverse environmental conditions where the plug is exposed to substances such as beer, sweaty hands, smoke and dirt its performance will ultimately be compromised. Over time the jack plug will lose it’s shiny appearance tarnishing to become duller in appearance as the copper and zinc react with the salts and acids in these substances. Tarnish is a layer of copper and zinc oxides (and other salts) which is a poor electrical conductor (an insulator). This oxide layer significantly increases contact resistance degrading the fidelity of signal transmission through the jack plug to the cable causing tone loss and a bad or noisy connection. This is not a irredeemable situation though as the barrel of a jack plug can easily be cleaned using very fine wool and solvents such as carbon tetrachloride (a degreasing agent) to restore it’s original performance. Brass jack plugs served the industry for many decades until nickel plating became a practicality.

Nickel Plated Jack Plugs

Nickel-plated jack plug with copper core

Nickel-plated jack plug with copper core

Nickel is much more resistant to oxidation than brass or copper and coating a jack plug with a thin layer of nickel prevents oxidation to improve it’s performance and durability. The process is technically known as electroplating. The nickel plating not only provides corrosion resistance but is also aesthetically pleasing because it doesn’t tarnish (it’s shiny). Nickel is also a relatively hard metal so that the plating is resistant to wear over time. The first practical bright nickel plating bath was developed by Max Schloetter in the 1930s and it is estimated that nickel plated jack plugs first became available in the 1940s.

Nickel is not completely inert though – it will oxidise or react in adverse environmental conditions or over long periods of time. Nickel oxide and its salts can be seen as a green discolouration or patina on the metal surface, but for all practical intents and purposes, under normal conditions it can be considered as being virtually immune to serious corrosion. Nickel plated jack plugs were a genuine step forward in terms of reliability and durability – I have nickel plated connectors that after 30 years of use where the brass underneath is only just starting to showing through. Nickel plated audio connectors were the industry standard for a several decades and used by players from Scotty Moore to David Gilmour to record some excellent guitar tones. However audio connector industry then shifted to adopt another plating material – gold.

Gold Plated Jack Plugs

Gold-plating might look pretty but is so thin and soft it quickly wears off to reveal the nickel plate beneath.

Gold-plating might look pretty but is so thin and soft it quickly wears off to reveal the nickel plate beneath.

Gold-plated connectors are a relatively recent development. They first became widely available in electronic hardware shops, such as Tandy (Radio Shack in the U.S.A.) during the early 1980s. They were real novelty at the time and there was an instant association with high quality because gold is a precious metal. One outstanding property of gold is that it is unreactive and exceptionally resistant to corrosion, only being attacked by a mixture of concentrated hydrochloric and nitric acids. It has far superior corrosion resistance in comparison to copper, brass and even nickel – if you happen to be playing guitar on the surface of Venus then gold-plated jack plugs are definitely the ones to use in this situation.

But gold is also a very soft and expensive metal. What this means in practical terms is that manufacturers deposit only the merest hint of gold plating, just enough to give the impression that the jack plug has a gold-like appearance. It’s so thin that it quickly wears off after just a few insertion/removal cycles of the plug to reveal good old nickel plating beneath. There were genuine technical justifications for plating connectors with nickel, however gold plating serves no practical purpose other than to act as ‘eye candy’.

Another property of gold is that it is an excellent electrical conductor. For comparison, if pure copper has a relative conductivity of 100 then silver is 8% higher, gold is 74% that of copper and nickel is 25%. As an aside it’s interesting to note that because silver is the best conductor silver plating is used for hi-fi phono connectors and has been used on test instrumentation connectors, such as oscilloscopes for many decades. It’s not been utilised on guitar connectors… yet. If taken out of context these figures could be used to suggest that gold-plated connectors are superior to nickel, however it must be remembered that the thickness of the surface plating is extremely thin. The guitar signal current flows through the plating and the metal beneath – through the metal core inside the jack plug.

The Core

The core is a metal rod inside the jack plug that connects the tip to solder tag housed within the barrel. The total resistance to signal flow is the resistance of the core in parallel with the surface plating. The core is typically brass, however there are plenty of eastern manufacturers that utilise steel, which is a lousy choice of material. Steel is not only a relatively poor conductor of electricity (3% that of copper) but also ferromagnetic – not a fantastic choice for an audiophile connector but it is cheap. A list of resistivities of metals and alloys can be found in the following table. Just testing a handful of audio connectors and adapters (of unknown origin and manufacture) that I had lying around in the workshop with a magnet revealed that ALL of them were magnetic. The lesson here is to know what you’re buying.

Some jack plugs are manufactured from steel and then plated with nickel or gold.

Some jack plugs are manufactured from steel and then plated with nickel or gold.

Unfortunately the majority of jack plug manufacturers do not openly specify the core material – possibly because it is not an obvious marketing point like the surface plating is. The only manufacturer I know of that does is G & H Industries in the U.S.A., who utilise pure copper for the core. Copper is an excellent choice because it is very good electrical conductor. Although German connector manufacturer Neutrik don’t appear to obviously specify the core material used in their jack plugs, a quick dissection of one reveals that it’s made of brass. And Switchcraft – a long established and reputable company – conspicuously state that they use a copper alloy (I’m reckoning that would be brass then?) for the construction of the core and sleeve. Brass and especially copper are both appropriate choices of material for the core, however it’s not a simple case of copper/brass verses steel. The quality of the copper and brass should also be considered. It should be realised that as these metals become scarcer, they are being recycled more frequently and as this process is repeated contaminants such as iron and steel are introduced affecting the composition of the brass. More information on issues affecting brass quality can be found in this well written short article ‘Getting Down to Brass Tacks on Quality’ by Jim Burstein. Both Neutrik and Switchcraft utilise single piece tip and rod construction, whereas the G&H rod is bonded to a brass tip. To summarise, the type of metal plating on the jack plug surface is quite literally just the tip of the iceberg. The internal composition of the core has as much bearing on the durability and tone of the jack plug as do the physical differences between gold, nickel or silver plating.

Insulators

Additionally, there are other internal factors such as the quality of insulation materials. Several different types of material have been and are utilised for the bushings and spacers within jack plugs, including hardened rubber, various types of plastics such as thermoplastic, mica, phenolic, fibreglass and nylon. Each material has its own strengths and weaknesses in terms of insulation resistance and durability and price. Mica is a superb insulator and resistant to high temperatures (again, suitable for use on for Venus) but brittle, nylon has good longevity in comparison to rubber and plastic because it more chemically inert. Many of these materials are excellent insulators and perform more than adequately in normal gigging/studio conditions. Some plastics do not have good long term stability and will consequently limit the life of the jack plug. There are countless types of plastics and it is impossible to know what you’re buying unless you purchase from a reputable manufacturer who specifies the materials they utilise.

One excellent type of plastic that seems to have been overlooked by jack plug manufacturers in the guitar industry is PTFE (polytetrafluoroethylene). This is often used in BNC connectors (for test instrumentation) and in the hi-fi industry for phono (RCA) sockets. It is and excellent dielectric, is immune to most solvents and acids, has a very high melting point (for a plastic), is extremely tough and it also has very low friction – practically perfect in every way for use as an insulator. A silver plated jack plug with PTFE insulators would be this engineer’s dream of something made from the appropriate materials with no corners cut.

Uh-oh, a Discussion on Quality

From a textbook engineering perspective it could be argued that even the poorest quality metal – steel in this instance – is a more than adequate material for the core and sleeve. Afterall the fraction of an Ohm resistance in a jack plug is vanishingly small in comparison to several thousand Ohms already in series with the signal from, say a passive pickup or a low impedance buffer (which may still be in the order of Ohms or tens of Ohms). So why all the fuss? Does it really matter? Well the issue here is that it’s not just that steel is cheap, it’s the CHEAPEST metal that can possibly used. Iron (Fe) costs less than $0.20/lb. Compare this to Nickel (Ni) at $8.40/lb, Copper (Cu) at $3.00/lb and Zinc (Zn) at $0.94/lb. When a manufacturer specifies steel over, say brass, that’s not an engineering decision, it’s an accountancy decision. There are no physical properties of steel that would encourage an engineer to even consider it in preference to brass, copper or a host of other more suitable metals and alloys. This then also raises further doubts and suspicions. If the cheapest metal is being used then what about the other materials and processes used in manufacture? Could insulation material be a poor quality plastic? Is the plating process well-controlled? Profits are surely the prime motivation here, not the desire for engineering excellence or a love of music. This is something I do not wish to support or be involved in. I want peace of mind that what I’m purchasing is a quality product, that the company who makes it is genuine and takes pride in their workmanship. Now that’s something I do want to be involved in!

A Final Note

How guitar cables and jack plugs affect the tone of the instrument has been known to catalyse heated debates amongst musicians and studio engineers. This isn’t helped by the unlimited ‘factoids’ in circulation on the internet or the ‘creative’ (often scientifically incorrect) marketing ‘flim-flam’ employed by some manufacturers in the relentless, competitve battle to differentiate their product from a competitor. My aim in writing this article has been to research and uncover the real science – the relevant engineering facts – of the materials and construction techniques used in the manufacture of jack plugs. To ascertain what is significant and what’s not so significant for good tone and reliablity. I welcome any comments or additional information that might help improve the content of this article. Thanks for reading.