Passive preamp buzzing?

[Marco]

This is the post from Jez that kicked it all off: http://theartofsound.net/forum/showt...732#post902732

Note my (initially) lighthearted response that followed, on post #183, and me challenging his assertion, which he's repeatedly swerved. Therefore, it wasn't ME who started that particular debate, so I'm not "forcing" anything from him, other than to explain why I'm supposedly wrong about what I wrote.

And what I'm supposedly wrong about, has got nothing whatsoever to do with electronics! It's to do with the (arguable) mechanical superiority of different plugs.

Marco.

[Barry]

Putting aside for the moment any discussion of differences in SQ, there is some difference in the quality and physical tolerance of RCA (phono) connectors and that of BNC and CAMAC connectors.

First RCA phono connectors were designed by RCA in the 1940s as a cheap way of connecting the pickup of a ‘phonograph’ (aka record player) to the audio amplifier of a radio set, replacing the far more superior but expensive ¼” telephone jack that had been used to date. The emphasis is on cheap. Both inner and outer conductors consisted of rolled nickel or tin plated copper sheet, with a disc of synthetic resin bonded fibre to separate the two. The American radio, TV and audio industry quickly adopted it as a standard.

After WW II the RCA connector was introduced to the fledgling Japanese consumer electronics industry, and because of that became the de facto standard for connector design for audio electronics. Over the years the original and simple design has been ‘tarted up’ through the use of better-machined conductors, now usually gold plated, and better insulating dielectrics, such as PTFE. The tolerance on the conductor diameters are still lax, which means some brands will have a tight fit when mated, whereas others will have a looser fit.

The outer diameter (of the socket) is 0.3” (= 8.25mm), and the diameter of the pin is 1/8” (= 3.175mm). However the outer diameter can be as large as 8.35mm, and the inner pin diameter can vary 3.0 ± 0.1mm; hence the variability in tightness of fit when the connectors are mated.


The BNC connector was designed from the outset to be used as a high frequency connector and one having a specific characteristic impedance. The concept of characteristic impedance has no relevance at audio frequencies, but it does impose far tighter tolerance on the dimensions of the coaxial conductors - far higher than that of the RCA design (which was not intended to be a constant impedance design). BNCs come in two varieties; those having a characteristic impedance of 50Ω and those having an impedance of 75Ω. For both the diameter of the outer conductor is 8.128 ± 0.025mm, whereas the diameter of the inner pin will depend on the characteristic impedance.

As such the BNC is a precision connector with less variation in the integrity of the connection when mated than the RCA. Interestingly, BNCs are only a little larger than RCAs and are only a little more expensive (though not as expensive as some brands of RCA). BNCs have one additional feature over the RCA, they are locked/latched when mated through the bayonet action of the plug.

For CAMAC connectors, I refer you to one manufacturer of such: LEMO https://en.wikipedia.org/wiki/LEMO. Suffice to say these are often the connector of choice in safety-critical applications, such as the nuclear and aerospace industry and for use in medical equipment. They are a little smaller in size than RCAs, but very expensive (although some brands of RCAs can be as expensive). Like BNCs CAMAC connectors also latch when mated.

http://theartofsound.net/forum/showt...dio-Connectors

[Bigman80]

Great Info Barry.

Sent from my EVA-L09 using Tapatalk

[walpurgis]

Connection related. It's strange how long it took for decent speaker connections to be available and to a general extent standardised.

Mostly, up to the later sixties dreadful little screw terminals were common on amps and speakers. Very prone to shorting and a fiddle to use, also precluding the use of substantial cables. Not that those were popular yet. Then DIN plugs and sockets came along, a slight improvement, but too small for decent cables and still prone to shorting if the plug wires came loose. In the seventies 4mm banana connections gained popularity. This made life much easier and opened up cable options too.

[Marco]

Thanks for that, Barry. Most enlightening, as usual

It's pretty obvious from your factual summary of events, showing that RCAs are NOT the optimum connectors for audio use, as the design never at any point originated from a desire to engineer it as being the BEST POSSIBLE solution. The emphasis was always on cheapness, not quality!

And as such, particularly in reference to the variable (and lax) tolerance on the conductor diameters, is a compromised design, being of overall inferior mechanical construction, compared with higher quality connectors, such as BNCs. It is therefore inevitable that RCAs, when compared with BNCs, will offer a connection with compromised integrity.

Having established the facts of the matter, I wonder if Jez will now have the grace to admit that not only was he wrong, in terms of completely misunderstanding the point I was originally making (I'll admit partly because I didn't explain myself as clearly as I should've done) about plugs, claiming that I was referring to sound quality, and perhaps apologise for that, but that he was also wrong by stating what he did below, in reference to the 'adequacy' of RCAs:

Once you had started with something like "I believe phono plugs are sub optimal and BNC's sound better", there is, as I am only too aware, nothing that I or anyone else could say that would result in you changing that to "now its been explained I can see that phonos are perfectly adequate for audio and there is indeed nothing to be gained by moving to BNC's"

We wait in hope! The key word there is "nothing", which as has been shown, simply isn't the case.

Marco.

[Firebottle]

BNC connectors aren't the easiest to fit onto cable, you have to cut accurately, plus they are not all the same with respect to the shield clamping.

I've done quite a few.....

[struth]

BNC connectors aren't the easiest to fit onto cable, you have to cut accurately, plus they are not all the same with respect to the shield clamping.

I've done quite a few.....

indeed, they are fiddly but so can rca's. at least when fitted they are pretty secure.

[Marco]

Sure, Alan, but nothing is perfect. And of course it's not about 'easy', if you want the best. You just have to take your time, use the correct tools (and cable), and do a good job.

The key with plugs or anything else, is to adopt the use of that which offers the least compromises, and from what Barry has written above, it's pretty obvious that, overall, RCAs are more compromised than BNCs

Marco.

[Thebiglebowski]

Sure, Alan, but nothing is perfect. And of course it's not about 'easy', if you want the best. You just have to take your time, use the correct tools (and cable), and do a good job.

The key with plugs or anything else, is to adopt the use of that which offers the least compromises, and from what Barry has written above, it's pretty obvious that, overall, RCAs are more compromised than BNCs

Marco.

Nope, BNC was designed for high frequency use and delivers no advantages at audio freqs.

RCA performs well above the requirements for audio and using BNC would not improve the sound quality. Your use of 'best' is nothing but your interpretation that something more complicated or expensive is better.

Just because A is more compromised than B does not mean that it cannot perform 100% of the requirements for a task.

[Marco]

Nope, BNC was designed for high frequency use and delivers no advantages at audio freqs.

For goodness sake, does anyone actually READ what I write??

I'm not talking about its performance at audio frequencies, or anything like that, I'm talking about its mechanical inferiority compared with a BNC!

Has it sunk in now?

RCA performs well above the requirements for audio and using BNC would not improve the sound quality. Your use of 'best' is nothing but your interpretation that something more complicated or expensive is better.

Well, your absolutist statement is no better or more valid than Jez's...

That *may* prove to be the case, but in terms of what *I* think on the matter, it'll be ME who's deciding that or not, not you, and forming my opinion accordingly. So don't come on here TELLING me what the result will be of something I test, as you'll receive very short shrift.

This is a staunchly subjectivist forum, and so ultimately we trust our ears here, above all else, and that's how it will remain!

Marco.