Now, although the gold plating on a jack plug has thousands of tiny pores in its surface, it’s not possible to observe them: to the naked eye, and a powerful optical microscope, the gold appears as a flat, smooth, unbroken surface. This fact makes it difficult to believe it’s actually riddled with holes. This got me thinking if there might be some kind if scientific experiment that could be performed in the average household to detect them. Gold is unreactive, so corrosive substances, even concentrated acids and alkalis, will have absolutely no affect on it. But what if, for example, hydrochloric acid (HCl) came into contact with the nickel beneath the gold? Could the acid penetrate the porous surface and attack the nickel to form nickel chloride? What would happen to the gold plate? Would there be any visible effect?
My experiment was simple: Immerse a gold plated jack plug in floor cleaner (which contains 16% HCl, essentially dilute hydrochloric acid) for a period of time and see what, if any physical changes took place. Below is a picture of a jack plug that had been immersed in a 50/50 mixture of floor cleaner and tap water at room temperature for 24 hours.
From the photo it can be seen that a substantial amount of the gold plating has vanished to reveal the nickel plate beneath. This was a surprise. Even more surprising: the nickel appeared unaffected by the acid. The acid was not stirred or agitated whilst the jack plug was immersed, suggesting the gold wasn’t mechanically worn away, but removed by chemistry occurring between the nickel plate and acid. The mechanism isn’t entirely understood, however it could be that the chemical reaction between the nickel and hydrochoric acid somehow dislodges the gold plate. Whatever the mechanism, the experiment has clearly demonstrated that the gold plating on the jack plug was ineffective as a protective layer against corrosion.
Now, gold plate does have its place in the connector industry. There are companies who manufacture high quality gold plated connectors for aerospace applications and for use in extreme environments, such as deep sea exploration. But the plating is either considerably thicker or it’s alloyed with cobalt and nickel (hard gold plating)—no evidence could be found that jack plug manufacturers do either of these things. For this reason it’s reasonable to conclude the 0.2μm of gold plating will do very little, or nothing, to improve the reliability or fidelity of the plug. It’s merely filigree gold decoration—‘eye candy’—that serves no practical purpose; and even fails at that, after a pitifully brief time. There is, however, sound technical justification for plating jack plugs with nickel.
Super Silver Conductors
Gold is an excellent electrical conductor, but silver and copper are better. For comparison, if pure copper has a relative conductivity of 100 then silver is 8% higher, gold is 74% that of copper with nickel trailing behind at 25%. On first glance these figures seem to suggest that gold plated connectors offer superior conductivity to nickel, but keep in mind 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. Silver plated connectors are frequently utilised in RF (Radio Frequency) and test instrumentation, such as oscilloscopes and signal generators, not only because silver is an excellent conductor but because it’s non-magnetic. Neutrik are one of the few manufacturers who utilise silver plate on their jack socket contacts, however silver has not yet found its way onto their jack plugs… yet.
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 series with the surface plating. The core is typically brass, however there are plenty of eastern manufacturers that choose to make it out of steel. Steel is a relatively poor electrical conductor (3% that of copper) and it’s also ferromagnetic—so not the best choice for an audiophile connector, but it is very 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.