[fihidelity]

Another question for you all. Is there any benefit attained by using RCA as opposed to 3.5mm to 3.5mm or RCA to 3.5mm? I'm think of buying/making and O2 amp and wonder if there would be any point fitting with RCA in.

 

[jaddie]

Quote:

Another question for you all. Is there any benefit attained by using RCA as opposed to 3.5mm to 3.5mm or RCA to 3.5mm? I'm think of buying/making and O2 amp and wonder if there would be any point fitting with RCA in.

So long as you use good cables and connectors, there's no advantage either way.  There are good quality connectors of either flavor.

 

[65535]

FWIW 3.5mm connectors are pretty dinky the only advantage is size and stereo capability in 1 connector. RCA connectors have much better contact and have less resistance, will this matter to sound quality, NOPE!

 

[jaddie]

Quote:

FWIW 3.5mm connectors are pretty dinky the only advantage is size and stereo capability in 1 connector. RCA connectors have much better contact and have less resistance, will this matter to sound quality, NOPE!

I'll take exception to the "less resistance" part, and the resulting effect on sound.  We are talking differences of tiny fractions of 1 ohm.  
FWIW, contact resistance, and far more importantly, reliability, is a function of contact material and contact point pressure.  Contact resistance becomes unstable due to oxidation.  Small point contacts have higher pressure per area unit squared, and non-oxidizing plating materials like gold prevent oxidation.  Once contact is made between two surfaces, both plated with gold, there's little if anything to be gained by increasing the contact surface area.  
 
Traditional RCA jacks have fairly large surface area contacts, thus the high pressure is required.  However, if both RCA and 1/8" are gold plated, there will be no difference in performance.

 

[jcx]

1/8" TRS do have consistently larger contact R than even like geometry 1/4" TRS, the smaller radius of 1/8" does give higher contact pressure but the surface area of the contact region is less
 
"better" connectors employ multiple contacts ranging from "bifurcated/dual beam" to Hyperboloid Contacts: http://www.qatech.com/IM_ContactBrochure10.pdf and "Louvertrack,  to "power bud"/"tribotech woven contacts": http://www.methode.com/Documents/TechnicalLibrary/PowerBud_White_Paper.pdf
 
its a real shame we're stuck with TRS as default headphone connection

 

[65535]

Quote:

I'll take exception to the "less resistance" part, and the resulting effect on sound.  We are talking differences of tiny fractions of 1 ohm.  
FWIW, contact resistance, and far more importantly, reliability, is a function of contact material and contact point pressure.  Contact resistance becomes unstable due to oxidation.  Small point contacts have higher pressure per area unit squared, and non-oxidizing plating materials like gold prevent oxidation.  Once contact is made between two surfaces, both plated with gold, there's little if anything to be gained by increasing the contact surface area.  
 
Traditional RCA jacks have fairly large surface area contacts, thus the high pressure is required.  However, if both RCA and 1/8" are gold plated, there will be no difference in performance.

 
 
I'm not sure why you took exception to parts of my post. They seem to completely agree. 

 

[jaddie]

Quote:

1/8" TRS do have consistently larger contact R than even like geometry 1/4" TRS, the smaller radius of 1/8" does give higher contact pressure but the surface area of the contact region is less

We should probably define what "larger contact R" means.  It's still vanishingly small.
 
Quote:

its a real shame we're stuck with TRS as default headphone connection

Totally agreed.

 

[jaddie]

Quote:

 
 
I'm not sure why you took exception to parts of my post. They seem to completely agree. 

I take exception to the following:
Quote:

 RCA connectors have much better contact and have less resistance, will this matter to sound quality, NOPE!

RCA connectors do not necessarily have better contact, and when we get into the area of contacts affecting sound quality generically, that's really a big problem, and loaded with a lot of misconceptions.  

 

[65535]

Decent RCA connectors have much more contact surface area than 1/8" TRS connectors.

 

[jaddie]

Ok, it's always good to check up on what's changed in connectors. 
 
First, most RCA connector manufacturers publish NO data on their connectors other than mechanical specs.  Switchcraft says nothing about contacts at all, same for Rean/Neutrik.  Kycon publishes a little data.  
 
The second thing to know is that the design of the inner contact on an RCA jack has changed somewhat, moving away from the full-sleeve design and toward smaller contacts.  This would be a good thing, as larger contact surfaces reduce pressure, and increase the chance for oxidation.  The new jack designs seem to have smaller dual-ridge contacts for the inner contact, and the same large cylindrical outer contact. 
 
So, given the limited data published by one manufacturer (Kycon), I find that contact resistance is stated as 30 milliohms for their average RCA jack.  Their contact material is tin-plated brass.
 
For 3.5mm stereo jacks, again very little data is published, again, nothing much from Switchcraft or Neutrik, but Kycon publishes a bit. Their average jack has stated contact resistance at 50 milliohms max, and contact materials are copper or copper alloy base with tin or silver over nickel plating.  None of that makes any difference to the contact resistance.
 
Both jacks are life tested for 5000 insertion/withdrawal cycles.
 
So, what I said was incorrect, and you guys are right, RCA jacks have, on average, 20 milliohms less contact resistance.  And, though I know I've seen them, I can't find any data on gold plated contact jacks of either kind.  
 
20 milliohms is 20 thousandths of an ohm. In the grand scheme, the difference between 30 milliohms and 50 milliohms is negligible.  It should be noted that those resistance figures are tested before a 5000 cycle life test.  Post-life test figures are not consistently published, but are typically higher by 2X.  
 
It appears that not all RCA jacks have higher contact areas than 3.5mm jacks.  The contact material in both jacks is not usually gold, as with small contact surfaces, a soft gold plating would wear off quickly, so manufacturers opt for a harder plating material, and depend on repeated insertions for a sort of cleaning action.
 
My apologies, all, for the misinformation.  My RCA jack data was outdated.  

 

[65535]

We can definitely agree that with good quality connectors made to spec that audio connectors will not change the sound quality.

 

[jaddie]

We can definitely agree that with good quality connectors made to spec that audio connectors will not change the sound quality.

Yup. Would it be too great a stretch to say that either RCA or 3.5mm could be good?

A small point, but the RCA connector was designed as a low cycle connector, in that you don't use it to connect and disconnect very often. The 3.5mm was designed as a front panel jack for frequent connection cycles. Today's versions seem fairly close in life expectancy, though.

 

[65535]

I've taken to using Neutriks Profi connectors which you definitely don't want to cycle often as you'll probably rip out your RCA jack on your component.
 
My biggest complaint with 3.5mm is cheap ones get loose too easily, and compared to 1/4" they pull out very easy. As a theatrical technician XLR is easily a favorite of mine with locking connectors and a solid design (10A per contact). They are bulky though.

 

[fihidelity]

Obese going to say that when the resistivity if a material is so low, the small difference in surface area is going to be negligible in the scheme of things.

I was thinking more along the lines of cross path distortion etc.

 

[Steve Eddy]

Quote:

Originally Posted by jcx /img/forum/go_quote.gif
 
"better" connectors employ multiple contacts ranging from "bifurcated/dual beam" to Hyperboloid Contacts: http://www.qatech.com/IM_ContactBrochure10.pdf and "Louvertrack,  to "power bud"/"tribotech woven contacts": http://www.methode.com/Documents/TechnicalLibrary/PowerBud_White_Paper.pdf
 

 
Look like a variation of Hypertronics' HyperTac contacts.
 
Quote:

its a real shame we're stuck with TRS as default headphone connection

 
But there are some alternative "standards." 4 pin XLR for example. They're even used by some manufacturers for outputs on amps with unbalanced outputs. Personally I'd go old school and go with screw terminals or binding posts. Hey, if dual 3 pin XLR's can become a "standard," why not?

 
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