Conductivity of materials and interconnects

[dfidler]

Hi All,

I'm going to take a tangent before getting to the point

<tangent>

I recently acquired a new [SnobFi - aka Classe DVD/SSP] system from ebay [for dirt cheap] and after hooking it up I got a really bad hum after turning on the amp. Strangely, the same interconnects were carrying signal from source components to my Class D AVR (and hooking the system back up to the AVR saw no hum).

After swapping a few cables out, the hum disappeared but that got me to thinking. All of my cables are > 15 years old and are probably due for retirement so I went out looking for new ones and nearly died when I saw the prices. It's impossible to get a decent cable for less than 20 quid, and they average 25+ (50+ quid for a 1.5m AES/UCB cable!?!?!?!)

So, the logical conclusion was that I could save myself a few hundred quid by DIY'ing my interconnects; naturally.

</tangent>

I've been googling interconnects quite a lot in my search for the perfect balance between performance, appearance [I'm shallow] and cost and I'm amazed by the prices that folks are charging for RCA and XLR plugs. What's got me wondering though all of the different platings that they put on these damned things.

Examples:

• Solid brass, silver plated then rhodium plated
• Solid copper, silver plated then rhodium plated
• Solid silver conductor
• Solid Copper, lacquered to prevent oxidation

I get that they plate the conductors to prevent oxidization (of copper or silver) but doesn't that basically nullify any benefit (increased conductivity) of using the exotic materials in the first place?

If I'm understanding conductivity correctly, you can increase the amount of charge that you can pass through a conductor by increasing the mass of the conductor (thereby effectively matching the conductivity of a better conductor).

So, in the case of using rhodium over silver over brass, the brass has 10000x the mass of the plating so it's, by far, the best conductor in the chain. The silver is mega conductive and then we come to the rhodium, which is 1/3 as conductive as the silver.

Okay, rhodium is durable, I get that, but I don't get what the purpose of the silver plating under it is. It seems like an excuse to charge 10x the price for the plug and that's it.

And is all of this moot anyways because of the ultra low current signals that are expected to go through your interconnects?

What am I missing?

Cheers,
Dave.

[nigelwright7557]

Bad hum sounds like a bad or broken connection.

While the purists will suggest the most expensive leads I personally just stick with basic leads like a mains lead for speaker wires and this works just fine.

However a piece of wire is not just a piece of wire. I did some research many years ago for a project and i was amazed how much the even the resistance of a piece of wire varies from manufacturer to manufacturer.
It is worth buying short lengths and testing the wire for resistance over a metre.

Another problem in amplifiers is connectors and I prefer to ditch them for soldered connections where possible.

[dfidler]

@nigel,

Interesting re: soldering, I've read that non-soldered connections are better; interesting.

[simon7000]

Originally Posted by dfidler

@nigel,

Interesting re: soldering, I've read that non-soldered connections are better; interesting.

Yes but whoever wrote that has no clue! Crimp connections with proper tooling has advantages but not for audio. Solder is at least 200 time better by measurement.

[simon7000]

Originally Posted by dfidler

What am I missing?

Cheers,
Dave.

Use an ohmmeter to be sure all the shields are actually carried to each end. Hum is usually a loose connector. Use deoxit on the connectors, be sure they are tight. Many prefer the sound of older cables.

[CopperTop]

Originally Posted by simon7000

Many prefer the sound of older cables.

Ah yes, many's the evening I like to sit in the garden shed and rub linseed oil from a rusty tin into some much-loved cotton covered silver wire that's been passed down through the family for generations. They say that when it was new it was a bit sibilant and had a narrow soundstage, but it's a deep chestnut colour now and sounds beautiful.

[noSmoking]

hi,
Just from my own experiences,I have found the yellow cable that usually comes with 2 audio cables to work the best ,I have found 2 types one is thin about a 1/8 of a inch,don't like it,the other size is almost a 1/4 inch it does the best sound wise and it works for a spdif cable, The 1/4 inch was compared to some other costly cables and the owners of the cable that was more expensive chose the 1/4 yellow and I was the one that switch them on him twice ,just my 2 cents,I haven't listen to the hundred $ or so more cables or some of the made for audio types,I have tried gold ,silver,and plated copper cores and can't tell alot of difference,I have experamented with 4" wires between componets just to see what cables do, The best length I have found especially for spdif is a meter,for speakers to a amp short as you can get them I used zip cord,14 ga.
I haven't tried cramolin B-5 or deoxit but acetone and pure alchol I have used and does work,check before and after you use it with a ohms meter and you can see,Check a soldered and a unsoldered connection (like rca,bnc plug) too,Just my 2 Cents!

[benb]

Originally Posted by dfidler

I've been googling interconnects quite a lot in my search for the perfect balance between performance, appearance [I'm shallow] and cost and I'm amazed by the prices that folks are charging for RCA and XLR plugs. What's got me wondering though all of the different platings that they put on these damned things.

Examples:

• Solid brass, silver plated then rhodium plated
• Solid copper, silver plated then rhodium plated
• Solid silver conductor
• Solid Copper, lacquered to prevent oxidation

I get that they plate the conductors to prevent oxidization (of copper or silver) but doesn't that basically nullify any benefit (increased conductivity) of using the exotic materials in the first place?

I really don't know what "lacquered" means in this situation, it seems the contacts would have to scrape through the lacquer to actually touch metal to metal and make the connection.

If I'm understanding conductivity correctly, you can increase the amount of charge that you can pass through a conductor by increasing the mass of the conductor (thereby effectively matching the conductivity of a better conductor).

Well, there's two things - there's the cross-section of the actual wire in the cable - resistance is inversely proportional to cross area (meaning a fatter wire is better), and directly proportional to length (meaning a shorter wire is better). But this is only important in very low-impedance connections, between an amplifier and a speaker. At line level, the resistance of even a thousand feet of wire is insignificant (but not its capacitance, but putting that aside...).

The other thing is the connector, specifically the mating between two connectors. This is critical in all cases, as the mechanical connection can be too weak (especially in RCA connectors) and/or too corroded to make a good electrical connection. That's partly what all these different platings are about.

So, in the case of using rhodium over silver over brass, the brass has 10000x the mass of the plating so it's, by far, the best conductor in the chain. The silver is mega conductive and then we come to the rhodium, which is 1/3 as conductive as the silver.

Okay, rhodium is durable, I get that, but I don't get what the purpose of the silver plating under it is. It seems like an excuse to charge 10x the price for the plug and that's it.

It has nothing to do with the overall conductivity of the metal, but rather how easily it can get tarnished and how well it conducts when it touches the metal contact in the other connector.

I don't know about this specifically, but what I recall reading about material A (the base metal of the contact )plated with B and then with C (the metal chosen to make good contact with the other connector) is that there's some good technical/mechanical/chemical reason that A plated with C won't work well, however A and C both get along well with B. Maybe someone with metallurgy and plating knowledge could be more specific. It's not about "what sandwich of metals makes the best conductor."

And is all of this moot anyways because of the ultra low current signals that are expected to go through your interconnects?

Yes and no - I do recall XLR connectors can carry a good bit of current, but none of that matters if connector surfaces are corroded and conduct badly if at all.

OTOH, I just use cheap cables and connectors (any "good" stuff I have is made with Belden and Neutrix), and when needed I wipe/clean any crud off the contacts and use "tweak" or whatever other contact deoxidizer that's available.

[auplater]

Oh goody!! another cabling-type thread...just what DIY Audio needs!!

technically, the short answer to your plating ?'s is

Copper can be a good conductor, but it corrodes, and then has poor surface conductivity... ditto for brass... what to do auntie Bee???

Why, let's plate them with sumthin better... maybe gold?? naw too expensive, and unless you put some of that nasty ole nickel under it, the copper will jump right thru the gold over time (known in the trade as a diffusion barrier)... and we all know that nickel just plain sounds cheap and cheesey, right?

How bout silver??? well the military uses alot of it, 'cause the corrosion products can be conductive (but not always)... okay, let's put a teeny weeny bit-o-rhodium (an uber$$$$ precious metal, but it's hard as H^%l and resists corrosion to anything except boiling 85% sulfuric acid) like maybe .000010" maximum.. yeah that works (used in microwave plumbing when cost is no object)

Does this clear things up???

I myself use el-cheap-o gold plated whatever I can find... seem to work for years, I usually toss the equipment b4 the cables wear out...

John L.

[Conrad Hoffman]

Keep in mind that the good 'ol RCA plug/socket is a hideously bad design, done way back in prehistoric times with low cost being the #1, #2 and #3 criteria. Plating it with gold is sorta polishing a turd, but it's better than nothing. I've used all sorts of connectors and frankly can't tell the difference between expensive gold and tinned brass as long as they're clean and have good tension. A shot of Caig DeOxit is a good idea too. BTW, never twist an RCA connector as you'll like as not twist off the center conductor of the wire if the pin turns. IMHO, the wire you use is more important than the connector, if the connector is at least halfway decent. Also, be absolutely sure to clean off all the flux after soldering. Rosin films will give you bad connections and water washable flux will corrode everything, giving you bad connections.