[time-nuts] DC distribution

[MLewis]

The bulk of my wiring experience is with residential electrical (VAC) 
and audio signal cables & speaker cables, with some VDC in amplifiers. 
Most of the computer cables I needed I could order, so I wasn't usually 
terminating them myself.

With audio, it's pretty straight forward. A number of people figure 
they'll save some money and avoid the snake-oil cable sellers and make 
their own cables. So they buy the materials that others have found work 
well, they'd make some cables, and report they don't sound good. The 
sound simply isn't clear. Many don't seem to be able to make a quality 
solder joint. When they get their friend who knows how to solder to redo 
the connections, and the sound is clear. Others get steered to the 
crimping connectors, but use pliers or cheap crimping tools. Again, 
despite quality materials, not a clear sound. They're just not a quality 
connection. So they can learn to solder properly, and be at risk of the 
typical stress failures of soldered connections, or the more robust and 
much easier to learn path, buy a proper quality crimping tool and learn 
to use it. Great connection and repeatable.

Then there's the soldered crimp. It's astounding the number of times 
such a connection fails and the wire: moves back and forth, turns in 
place or pulls out. The heat from soldering expands the crimp, lowering 
its crimping pressure, for a poor crimp connection, but it's still tight 
enough while heated that the solder can't wick in. You end up with the 
combination of a poor crimp connection and a poor solder connection. I'd 
guess that with a poor enough crimping, there could be enough space to 
wick solder in...

An engineer told me what was up, and I cut open some connections that 
seemed solid to check. In each case there was a gob of solder at the 
end, but only some trace solder within the first part of the strands, 
with minimal contact between the wire and the crimp. I've cut one open a 
number of times over the years since, to show such to people. (Note: 
NASA will not accept crimped connections of tinned stranded or tinned 
solid wire. I've no idea why, but I figure it's a given that they know a 
lot more about terminations and connections than I ever will.)

So my first-hand personal experience is that I've seen dozens upon 
dozens of examples over four+ decades where an audio cable terminated 
with soldered crimps that did not sound clear, but replacing the 
terminations with properly soldered or properly crimped connections and 
the sound was then clear. Not a subtle difference, but at minimum a 
strong improvement, and usually a night and day difference. Now for 
quality consistency, I only use crimps for audio connections and choose 
connectors accordingly.

I've heard a lot of speculation over the years as to why this difference 
in clarity, but nothing that seems completely credible. The closest to 
credible speculation I've heard is:
- a poor connection results in multiple signal paths resulting in a 
sightly overlapped signal so the signal is no longer clear, or
- a poor connection has multiple connections and combined with eddy 
currents in the connector you can get tiny RC paths instead of a single 
long connection, so you've got multiple re-injections of a delayed 
signal that smooths tiny changes in voltage, which is your signal.
Causation is clear. The explanation? No idea.

I've heard people say that all this analogue cable stuff doesn't matter 
for digital signals because it's digital. Except that if one reads the 
specs, the "digital" signal is really an digitally encoded analogue 
signal. Back in the main-frame era, a number of times I was able to 
correct throughput degradation or outright failure by addressing cable 
issues (poor connections, shielding grounding, co-located cables of 
identical length so they're sometimes surprisingly effective as 
sending/receiving antennas, etc.) that techs thought would only apply in 
analogue signals.

So where someone is transferring a timing signal down a cable, depending 
on the frequency a quality termination/connection may be important, not 
only to the longevity of the cable, but to the quality of the signal, 
hence the ease, speed or consistency with which it drives and triggers 
what is reading it.

And for power connections, you don't want to hope you detect the signs 
of a failing loose connection due to heat, arc smells, etc. (like the 
mushroom-cap screw heads on terminations for containment & detection), 
before it outright fails, nor a conductor that comes free if the 
wire-to-solder connection breaks. The welded connection is new to me, 
but sounds like it could befit in some applications. If you've enough 
power and the connection is not tight, I have seem some conductors weld 
themselves to a terminal, often with a thin connection; but usually it's 
material gets blown away and the conductor is now loose. Lithium battery 
packs can deliver some surprising current.

So again, I don't think doing a proper (or poor) crimp connection, then 
expanding it with heat to try and wick some solder into gaps that would 
have been reduced by crimping and then with heating, is a very good way 
to go, along with taking on the risk of the stress failures of soldered 
wires.


On 05/10/2019 2:10 PM, Wes wrote:
> On 10/4/2019 12:17 PM, MLewis wrote:
>> With audio signals, a soldered crimp is one of the worst possible 
>> connections.
>
>  Please explain.
>
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