I couldn’t understand why the sound i was getting deteriorated over about a three to six month period. In the end i decided that this might be due to Galvanic or bimetallic corrosion.

This type of corrosion is an electrical and chemical process whereby a metal corrodes when in contact with a different metal. Three conditions need to be met for the process of galvanic corrosion to occur. one there must be two dissimilar metals; further
that there is an electrical current flow between them and finally that there is conductive fluid present between them. The initial reaction is to say that this third condition is not met in RCA hookups. However RCA interconnect plugs and sockets are
hardly a perfect fit and interconnect contacts will be coated with miniscule amounts of water. Water is a conductive fluid and is present in varying amounts in the air as water vapour. Hence the conditions of galvanic corrosion are met where the plug and
socket plating metal is different. This type of corrosion will be more likely in humid and salty climates. Somewhere like Las Vegas has a low humidity and will likely be a low corrosion spot while San Francisco has relatively high humidity and will have
higher incidence of mating corrosion.

The following table gives a measure of likely galvanic corrosion of four popular interconnect plug/socket metals. A high galvanic value is about +/- 4 and the lowest is zero. Values under +/-0.3 are considered not significant.

Silver Gold Copper Nickel
Silver 0.0 -0.7 -0.46 -1.05
Gold 0.7 0.0 -1.16 -1.75
Copper 0.46 1.16 0.0 -0.59
Nickel 1.05 1.75 0.59 0.0
Source: Dissimilar Metals And The Risk of Galvanic Corrosion in Mating Connectors
July 23, 2015 By Danny Boesing

The larger the value the larger the likelihood of corrosion. So the worst case for corrosion here is using a gold RCA plug connector on a nickel socket (1.75) or vice versa. While having a silver plug on a copper socket is the lowest (0.46). I surmise
that the period over which the process takes will depend largely on local humidity conditions, the level of current, how often the plugs are plugged and unplugged and there maybe other factors. Someone in a low humid climate might have a very different
experience of corrosion and its impact on sound compared to someone living in a high humid location. While plugging and unplugging might scrape away the corrosion.

It is true some metals can better withstand corrosion than others. Nickel, silver and gold are supposed to withstand corrosion quite well. Again maybe what we are talking about is over what time period and in what water vapour conditions. And further
what we’re really interested here is the impact of corrosion on sound and an answer to the question: how much corrosion needs to occur to impact on sound?

The corrosion happens slowly to begin with, and is not visible to the naked eye. I find that i’m just listening and then suddenly one day it dawns on me that it’s all a bit rubbish and that the sound has deteriorated. What’s needed - new tweeters?
new interconnects? a new player? Corrosion results in distortion. The treble balance is awry, there’s a noticeable and annoying ringing or hardness in the upper octave mainly heard with solo piano recordings and other parts of the frequency are
affected. It just doesn’t hang together any more. There is an improvement after a contact clean. That gives you another 3 or so months.

What’s the answer? Use amounts of deoxidizing solution. I’m not sure how long these solutions work for. I have just started experimenting with this on an op amp fitted into a plated (gold or copper) socket. You coat surfaces with the deoxidizing
solution and it should work and stop the corrosion whatever the corrosion source. I’m wondering if contact grease or lubricant, like electrolube, will have a similar effect. Surely contact grease would keep water vapour out. I have not tried this
though.

An alternative solution is to choose connectors with similar plating materials. This should be easy to do if you DIY your own cables. It just means matching nickel plugs to nickel sockets, gold plugs to gold sockets and so on. And depending on your
system you might end up with interconnects with nickel plugs on one end and gold plated plugs on the other. The point being galvanic corrosion only happens with bimetal contact present once you take this out of the equation galvanic corrosion doesn’t
occur. I suppose a difficulty with this approach is that you need to successfully identify the plating metal of the socket connector. For instance some coppers can be mistaken for gold. And so called Nickel sockets could be a combination of metals. And
the process is upset when plug connectors are say rhodium plated, silver is sometimes rhodium plated to stop it tarnishing, unless of course you have rhodium plated sockets as well.

I did change all my connectors so that each plug and socket had similar, as far as i could tell, plating materials. And there has been no deterioration in sound so far. And, for some of the cables, that was over 6 months ago. So for me this seems to be
the solution. it was a leap of faith the first time i fitted a nickel plated plug - i mean they’re so cheap that they did not inspire a lot of confidence. But it worked fine and sounded good.

So do RCA plugs/sockets have a galvanic corrosion problem? I believe so though part of me is not convinced about the conclusion as surely someone somewhere would have spotted this earlier. Galvanic corrosion is a type of oxidation and comes under the
general heading of oxidation which has many interconnect and cable references. i suppose, also, there might not be a lot of interest in this. after all corrosion is corrosion, whatever the source. Does it really matter about the source of corrosion?
There is also electrolytic (non-contact) corrosion. Galvanic corrosion can be described as a contact corrosion between dissimilar metals and also as a special type of electrolytic corrosion. I’m not sure how you would tell the difference between the
types of corrosion. Perhaps galvanic corrosion happens at a faster rate than oxidation because of the presence of current and bimetal contact though water vapour is present for both.

has anyone found similar in their set up? and what do you do about it?

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Short answer:

Yes, they *can* have a galvanic corrosion problem.
However, it is a very easy problem to eliminate.

Getting down to specifics with some background first:

a) Gold is not a particularly good conductor, and when alloyed, even less so. It was chosen for use mostly in aerospace applications as it is resistant to corrosion, so in a satellite application, the high cost was not an issue - as one example. Gold
moved into audio applications mostly because a class of vendors and merchants determined that a few cents worth of gold was the functional equivalent to many dollars worth of profit. And an entire industry was born around boutique cables for which there
is not one single, solitary comprehensive study in its support.

b) Fine silver is very nearly as resistant to corrosion as fine gold, and as close as there is to a room-temperature super-conductor. Coin or sterling silver is subject to sulphur corrosion (not oxidation), which as we burn less coal is reducing somewhat.
But either is still a better conductor than copper or gold.

c) Cadmium, the once-and-former plating-of-choice has (rightfully) fallen out of favor based on its toxicity (why did Van Gogh cut off his ear?). In any case, cadmium salts are not happy in a low-voltage signal path - they can rectify (act as a diode)
at rF frequencies, often with unfortunate effects.

d) As the snake-oil industry has yet to use fine silver for jacks and plugs, and as gold is a poor choice for audio applications anyway, the best choices are either nickel or tin. As a plating material, tin is a very slightly better conductor than
nickel. As a wearing material, nickel is both better and much harder than tin as well as being slightly more lubricious.

Cutting to the chase: Most base-metals for jacks and plugs is either spring bronze or brass, with bronze being the better for jacks, and brass being the better for plugs. Tin takes solder better than nickel - and soldering nickel directly requires skill
and the correct materials and tools. You will find that high-end nickel plated jacks have tin-plated soldering lugs for that reason. As a matter of good habit, one should remake all audio connections at least once per year in a conditioned climate, once-
per-quarter on the West Coast, eastern Mid-West or South, and twice per year on the East Coast. All of them - speakers and patch-cords. Four times per year anywhere in England or Europe. Saudi, Dubai (UAE) once per quarter as with the Middle East in
general. I have not experienced other regions or climates for long enough to advise, but the more polluted, or closer to salt-water, or high humidity, the more frequent the need.

DO NOT:

a) Use any sort of chemical anti-oxidant. The material is persistent, and if not entirely and completely removed after use, the reaction(s) will continue until the active materials are consumed. Not good.
b) Use any sort of conductive abrasives such as steel wool, nail-file or similar.

DO:

a) Use a non-conductive soft abrasive such as a drafting eraser. I have found that the best tool on the planet for the purpose is an electric drafting eraser with a soft element. https://i.ebayimg.com/images/g/G1YAAOSwJLde1vFG/s-l1600.jpg I keep one
of these with a life-time supply of elements (these are also excellent for cleaning circuit-board, connectors, tube-pins and similar).
b) A variety of dental-picks can be your best friend for tightening jacks and cleaning corners on plugs - if needed. *ALWAYS* do this when doing the service in any case.

Keep in mind the nature of the beast. For the voltages, surface areas, and cord-lengths under discussion in the Audio World, metals, alloys, and materials are largely irrelevant making the first-assumption of well-made items and appropriate means,
methods and materials in the first place. So, tin-against-nickel-against-copper-against-gold-against-tin-against-brass-against-bronze, if kept clean and tight, is all-the-same in the real world. To the chagrin of the snake-oil distributors and the
boutiques that they support. Good tools are seldom overly complicated. Overly complicated tools are seldom good.

Enjoy!

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)