Written by 5:00 am Cables

Still More Merry Metal Madness

Roger Skoff posts Part 8 of his occasional series on weird things about cables

In the last couple of installments of this continuing series, I wrote about RCA connectors, touching on their impedance weirdnesses and on potential problems with magnetism and the metal that they’re made of. In this one, I want to continue with that subject and, hopefully, finish it off and go on to other connector issues.

One of the probleneutrik_profi.jpgms that I, and probably most other audiophiles, have had with RCA connectors is that they are normally designed so that the “hot” lead (the center pin) of the male connector makes contact with the hot lead of its matching jack before ground connection (by the outer ring) is made. The result is that — because all of us are at one time or another either lazy or forgetful — at least most of us have found ourselves either making or breaking an RCA connection the wrong way and being treated to (at least) a loud horrible noise from an ungrounded “hot” lead or even to some blown speakers and/or electronics.

The way you’re supposed to prevent such problems is to either turn off the equipment that you’re making or breaking contact with or to at least set (if it has one) the selector switch on the next device down-line to some other input before making or breaking the connection.

The proof that — even if you haven’t personally experienced them — loud noises and blown speakers or electronics are common problems with improper RCA connection can be seen in the fact that no less a company than Neutrik, a respected Liechtenstein connector manufacturer heavily into pro audio, has seen fit to design a product — the Neutrik Profi RCA connector — to protect against them. The Profi connector, unlike other male RCA connectors (except, of course, Profi imitators, if there are any) makes ground connection first and breaks ground connection last, so there’s never any risk of embarrassing or expensive consequences.

The way it does this is by keeping a relatively conventional center (“hot”) pin, but breaking the ground connection into two pieces: one fixed and one able to slide forward to beyond the center pin (on most male RCA connectors, the center pin extends 0.3 inch [7.62mm] or even more past the ground ring) so that the ground connection is always already in place when the hot connection is made or broken. Neutrik does this by placing a spring between the two halves (fixed and moving) of a two-piece ground contact assembly, to both control the movement of the front (moving) piece (sometimes called the “foreskin”) and to maintain constant electrical contact between both pieces.  

If there are problems with the Profi connector, it wouldn’t surprise me if some of the biggest come from that one little spring.

ALL connectors, of any kind or style, have touching or sliding contacts in them somewhere. They have to; otherwise you would neither be able to make or break contact with the matching connector of the opposite gender. With the Profi RCA connector, however, there’s not only the expected push-on between the two hot contacts, and the two ground contacts to make the necessary male-female connections on both sides of the circuit, there’re also two more press contacts: between the fixed part of the grounding assembly and the spring, and between the spring and the moving part of the assembly.

The other contacts can’t be avoided, and so are irrelevant, but those two extra press contacts per connector are two more points of potential resistance and/or potential signal degradation as compared to other, more conventional, RCA connectors.

The fact that the springs are springs is significant, too: The most likely materials for them to be made out of are beryllium copper, phosphor bronze, and steel, which have, as compared to copper’s 100% or greater IACS conductivity. IACS conductivity ratings of (for C17300, C54400, and the high-alloy steel that springs are typically made of) just 22%, 19%, and less than 3%, respectively.

To put those numbers in some kind of usable perspective, consider that even though XLO, my former company, regularly used Tellurium copper (IACS 93%) in its premium RCA connectors, the great majority of RCA connectors from other manufacturers are made of “free-cutting” (C36000) brass and have a stated IACS conductivity rating of just 26%. If that’s also the case with the Neutrik Profi RCAs, even as low as the conductivity of the connector itself may be, the conductivity of the spring is still anywhere from “somewhat” to “very significantly” lower, which creates another potential problem. And if the spring is made of steel, that problem is further complicated by potential problems of magnetism and its effect on the carried signal.

In evaluating the Profi RCA connector, something to always remember is that Neutrik, the company that makes it, is very strongly oriented toward pro audio — sound reinforcement, recording, and broadcast applications — and that for those applications, unlike for the usual home hi-fi system, connections are constantly being made and unmade to deal with constantly (daily or even many-times-daily) changing system requirements. For Neutrik’s pro users, it may very well be that reliability, durability and the ability to make quick and safe connections without blowing anything up (all things that their extremely popular XLR and speakON quick-change speaker connectors are famous for) are more important than absolute sound quality, and in designing the Profi RCA connector, they may have brought those concerns to the home hi-fi market, where they may not necessarily apply.

For ultimate-performance applications like high-end audio (anywhere other than in a dealer’s showroom), connections once-made are likely to stay made for years at a time and, even for dyed-in-the-wool Hi-Fi Crazies and professional audio reviewers (who DO make changes much more often), the very best possible sound quality, if it comes to a choice, is likely to trump safe quick-change features every time.

And that means that the spring probably has to go. Just as the weakest link in a chain will limit the strength of the whole chain, so any excess resistance (reduced conductivity) anywhere along the line — in this case, in the Profi connectors at both ends of a set of interconnects — could be a limiting factor on their performance, and where total performance is the goal, that may not be acceptable.

Another thing about connectors that reduces their conductivity as compared to the copper (or silver or silver-plated copper) of the wires of the cables that they terminate is the plating on the connectors’ pins and ground rings. Years ago, Enid Lumley wrote (in The Absolute Sound) that she heard significant differences from scraping this off. I’ll take a look at that in the next installment of this continuing series.

Hopefully, I’ll see you then!

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