Metal to Metal

Considerations on metal to metal junctions in an audio signal pass

Part One

Very subtle changes in sound may occur at the junctions between different kinds off metal. Plugs and sockets affect sound, as do wires. Sometimes the quality of a cable depends depend on how the wire is attached to the plug at each end.

For example, after the insulation was cut away, was the exposed wire scraped to remove the copper oxide from it's surface before it was attached to the connector?
Was the wire physically crimped onto the connector under high pressure to form a real metal-to-metal connection before soldering? (if not, the solder – itself an alloy of tin and lead – may become the conductive pass). In cheap patch chords the connection may not be soldered at all and the wire may simple be held on the connector by melted plastic. It's a shame that hi-end cable manufacturers don't discuss these construction quality issues in their ads, instead of promoting silly mythologies…

The plug or socket typically has a core of brass ( an alloy of copper and zinc ) with a shiny nickel exterior. In some connectors the nickel is covered with a molecule-thick "flashing" of gold, to produce an appearance of costly quality and perhaps also to prevent the slow corrosion that occurs in most metals when they are exposed to air.

Consider all these metal to metal junctions that an audio signal's small electrical current may have to flow through when we plug a cable into a socket:

Beginning in a copper wire, emerging though the wire's unscraped copper-oxide surface, then passing though a layer of solder (tin and lead ), trough the nickel plating on the metal tag where the wire is attached into the brass core of the plug, out through the layer of nickel ( and perhaps gold) on the plug's contact surface then into the mating gold of the surface of the socket , through the nickel plating into the brass core, out through the nickel plating on the socket's wire tag, through more solder to another layer of copper oxide, and…( uufff! ) finally into the copper wire that will carry the signal to the next stage in it's journey.
No wonder some designers prefer to have fewer plug-in connections in the signal path!

Part II

Wipe the switches, mate.

Most electrically conductive metals undergo slow corrosion on surfaces that are exposed to air, humidity, pollution, and finger print oil.
This applies also to the electrical contacts in mechanical switches.. Two metals are exception to the rule: silver and gold. (Some of the best switches use solid silver contacts, but they are costly. Solid gold might be even better but would be ridiculously expensive. Gold plating, or flashing, doesn't help much in switches because in a well-made switch the contact surfaces scrape against each other under pressure each time the switch is operated.. This wiping action would soon scrape off the plating, exposing the brass contact surfaces you started with.)

The wiping behaviour of switch contacts is an important part of their design. Each time a switch is used the accumulating corrosion on its contact surfaces is scraped away.
Result: a switch that is used every day is likely to be trouble free. But, a switch that is used only once a month may develop a significant film of corrosion on its contacts. Someday this will become obvious when your left channel disappears into the void…Long before the signal vanished it was slowly being corrupted by low-level rectification at the contact points.

Preventive maintenance is as easy and important as brushing your teeth: periodically, and immediately before every important listening session, exercise every switch in the signal path a few times to wipe its contacts clean. Indeed, one of the unwritten rules of good engineering design is that the only mechanical switches in the signal path should be ones that will be used often; example: the input selector. Switches that will be used occasionally, such as a tape monitor or tone-control bypass, imo should be design so that in normal use the signal need not pass through a set of contacts.

These considerations applies to mechanical switches that actually conduct the audio signal, not to electronic switches. In the latter, pressing a button simply sends a DC voltage to turn on a transistor, which conducts the signal. Most of the switching in cd players, dvd's and in modern tv's is electronic, but mechanical switches are still very common in preamps, amps and vintage hi-fi components.

Part 3

Wiping action was also built into the design of the RCA plug, but it provides no benefit if it isn't use. If we leave the cables from your TT or CD player plugged into your preamp/amp for three years, we aren't doing anything to prevent low-level rectification at the socket.

To prevent a clean signal path, every few months we should unplug and re-plug every cable in our system a few times to wipe the contact surfaces clean.
This is so beneficial that when somebody marvels at the sonic benefit of a new interconnect cable ( and I believe some cables are better than others), I often wonder how much of the improvement was due to simply to the wiping of the plug contacts that occurred when the new cable was connected.

Also we must consider the bare-wire connections for speakers. A half-inch (12mm) of insulation is stripped off each end of the wire, and the bare copper wire was connected to the terminals. The problem is that unlike nickel-plated phono sockets, where corrosion is slow and subtle, the corrosion of exposed copper is rapid and serious; and as we know copper oxide is a poor conductor of electrical current.

There's a simple way to provide a secure, corrosion-free, high-current connection from amplifier to speaker: install a connector terminal on each end of the wire. The connector should be a "U"-shaped spade lug, a hook-shaped lug, or a banana plug. In any case the wire should be crimped onto the connector with high pressure to make a good metal-to-metal connection, then soldered.

Contrary to popular impression, the object of soldering is not just to secure the electrical connection. By flooding the wire-to-connector joint with a heavy liquid metal that solidifies as it cools, soldering seal out air and guarantees a perpetually corrosion-free joint.

As a final note and because everything in audio matters: a metal-to-metal good connection corrosion-free has imo a great sonic impact in every good hi-fi system.

I wonder if anyone has ever made an IC or speaker wire out solder just to see if it degrades or improves the connection.

With my new Nordost cables i don't have the need to solder the bananas because it came with soldered bananas from factory, but i think that a good metal to metal solder is better than any banana's screw mechanism.

As you might know - and i know you do

- we can screw tight a joint or a cable , but after a few months and mostly because of temperature variations the screw will not be so tight anymore. Sometimes is even loose... adding to that copper oxide and you have a great resistance, hence the loss of signal or a deteriorate one.

From a mechanical and electronic point a view, nothing's better to a metal to metal connection than a good solder. Anything that improves a good connection also improves audio signal path.
For convenience and other factors we can adopt for a screw mechanism.

This is an extremely interesting thread soundt/thumbup.gif

. It reminded me of an article I read in Stereophile way back. So I hunted around and found the magazine, volume 20 #2 Feb. 1997.

The Music Sciences O2 blocker anti-oxidant systems, very good read, I can't get on the site to link it for some reason

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You can put pads inside your components to prevent the nasties on the inside and use the wipes for the connectors. This may be old news by 2008, just sharing.

Apparently a blend of amine carboxylate chemicals known as VCI's. Used by various military and shipping container companies.

There's phone #'s if they're still valid, it's Sunday as I post this, so....maybe call tomorrow:
(800) 883-1964
Local in St. Paul
(612) 405-0825

Craig