[sdiy] "Mini-jack" myths

[flightofharmony]

This is one of those subjects that is plagued by misconceptions and urban
legends which just won't die - and it keeps coming up. I did a lot of
research into this when I started building, and here's the details I
discovered. But first, I want to make it clear that this is based on that
research, which is still ongoing, and that nobody can ever know everything
about anything, so I welcome any additional information or corrections - as
long as they are politely-worded and include actual details and not just
hearsay. In addition, I do not cover (or care, just yet) any new variations
on this theme, as most are platform-specific and yet available to the
general public.

While there is a large body of misinformation in audio electronics, this is
one area where blindly following the common opinion can actually cause
physical damage to your equipment, so we'll start with:

There is no such thing as a 1/8" telephone (also called "phone") jack or
plug - at all, ever.
I blame Switchcraft for propagating this myth. As far as I have been able to
find, they chose uncommon fractional sizes for their smaller jacks (9/64"
and 3/32") which use too many syllables when spoken and were not
commonly-available characters in typesets for the printing presses of the
time, so they rounded to the nearest common designators (1/8" and 1/16"). 

9/64" = 0.1406" = 3.572mm
1/8" = 0.1250" = 3.175mm
3.5mm = 0.1378"

7/64" = 0.1094" = 2.778mm
1/16" = 0.0625" = 1.588mm
2.5mm = 0.0984"

Switchcraft sizes:
"Tini" = 0.141" = 3.581mm
"Micro" = 0.097" = 2.464mm

"Mini-jack" is the term often used to cover a large range of different
jacks, namely: "Tini", 3.5mm, 2.5mm, and "Micro". The only consistent aspect
of these jacks is that they are all smaller than the old 1/4" standard jack
used originally for cross-patching telephone circuits. "Micro-jack" is
sometimes used to describe the two smaller formats -  2.5mm and 0.097". For
the rest of this I will focus on the 3.5mm and 0.141" sizes.

These sizes are *not* mutually interchangeable.

A 0.141" plug in a 3.5mm jack will often damage the leaf contacts in the
jack, shortening the life. Sometimes the jack will be ruined for 3.5mm
plugs.
A 3.5mm plug in a 0.141" jack will often work, but that depends upon which
0.141" jack. The plug will sit a little loose but still make contact, but
switched jacks usually do not switch - particularly the Switchcraft 142.

Switchcraft:
They make excellent jacks and plugs, don't misunderstand that, but they are
very American in their approach to metric sizes (and change in general). The
only 3.5mm jacks that they *manufacture* are the 35PM1 and 35PM2. All the
other jacks *offered* by them are manufactured overseas. In fact, they are
standard offerings from a large number of Asian companies.
The only 3.5mm plugs that they *manufacture* are the 35HD series. They are
very nice plugs! But they are only available in stereo configuration.
I had a meeting with the Switchcraft Northwest regional manager to discuss
custom jack designs, which is where I learned a lot of this. Also that they
have no interest or inclination to pursue any metric products.

Plug geometries:
This is the shape of the plug when viewed from the side. The initial angle
of the tip, the distance of the first "lip" from the tip, and the angle and
curvature of the notch.
There are several different geometries floating around, but very little
information that I could find. Some jacks are intended for a particular plug
geometry, while some are apparently "one size fits all" with accordant
results. 
Mis-matching plug and jack geometries can have various effects:
Plug seats early or late
Plug does not seat perpendicular to jack
Bad or intermittent connection
Plug retention feels loose or "about to pop out"

The most common style seems to be what has been termed the "japanese" style:
a steep (~45°), flat rise from tip to ridge, sharp angle at the ridge, a
shallow (~15°) slope to the notch, and a sharp angle at the notch. Most
european jacks are intended for these. The other styles may have:
rounded top to the ridge
rounded bottom to the notch
Different slope angles
Rounded slopes - convex or concave
Spherical tip shape

"Cheap Chinese jacks"
Racism is appalling, no matter the form it takes. 
Re-posted from MuffWiggler:
'People complain endlessly about "that Chinese crap", but it would not even
be on the market if no-one bought it. When it comes to components, the
motive behind production is fulfilling a customer's specifications. Very few
(relatively) component manufacturers are in the innovation area of
manufacturing, most are bespoke or custom shops [This is particularly true
of Asian manufacturing]. Nearly all of the components that they offer were
originally design by someone else for their own product line and, once the
orders are filled, the component manufacturer still has all the tooling for
that product, so they make it available to others.'

It wouldn't be available if people would just stop buying it! So where does
the blame truly lie? Furthermore, much of the "crap" manufactured in China
is designed by companies in other countries. China just gets the blame again
- *for making what they were told to make*.

Best regards, 

~flight
flight at flightofharmony.com
http://www.flightofharmony.com