[GreenKeys] half normal phone jack?

[Don Robert House]

Thanks to Roy Morgan I do not have to write all of this out with my  
bum fingers...

Jacks and Plugs

1. There are two sizes of patch bay jacks and plugs. The bays used  
with approximately 1/4" diameter plugs are known as Longframe, while  
the bays used with 11/64" diameter plugs are known as Bantam, TT, or  
Tiny Telephone. A Whirlwind Longframe bay has 24 jacks per row  
providing 48 patch points (also referred to as a 48 point patch bay).  
A Whirlwind TT bay has two rows of 48 jacks each, providing 96 patch  
points.
2. Wiring The convention for patch bay wiring is that they are  
configured with two rows of jacks, one above the other, with the top  
row wired to equipment outputs, and the bottom row wired to equipment  
inputs. The jacks are numbered in a standard left to right,top to  
bottom scheme (Top Row: 1-24 LONGFRAME or 1-48 TT, Bottom Row: 25-48  
LONGFRAME or 49-96 TT).

3. Normalling Typically patch bays are wired so that with no patch  
cables inserted, each jack in the top row is "normally" connected to  
the jack immediately below it in the bottom row. By planning your  
wiring in advance, this arrangement will automatically connect the  
outputs of equipment (wired to the top row jacks) to the inputs of  
other equipment (wired to the bottom row jacks) in the most often  
used configuration. Then, when you need to do something special, you  
can insert patch cords and change the way signals are connected.

There are two common forms of normalling: HALF NORMAL and FULL NORMAL.

HALF NORMAL (HN) The top row jacks are connected to the corresponding  
bottom row jacks through switching contacts in the bottom jack. When  
you plug a patch cord into the top jack on an HN patch bay, the  
output signal wired to that top jack stays connected to the jack  
below it. At the same time, the output signal from the top jack is  
now connected to your patch cord and can be plugged into another  
input jack on the patch bay or connected directly to another piece of  
gear. The result is one output going to two inputs.

Only when you plug a patch cord into a bottom row (input) jack on an  
HN patch bay is the "normal" connection disconnected between it and  
the jack above it .

FULL NORMAL (FN) uses switching contacts in both rows of jacks.  
Plugging a cord into either the top or bottom row jack of a full  
normalled bay disconnects the "Normal" signal flow from the top to  
bottom jacks.

4. Grounding Grounding throughout a patch bay wiring system can be a  
complicated issue. To keep ground-loop induced hum from entering your  
system, it is important to decide on a uniform method of  
interconnecting equipment chassis grounds and audio shields.  
Individual situations may require different solutions regarding what  
type of grounding configuration will be most effective. Consequently,  
we offer four standard configurations for the termination of shields  
at the patch bay. These options are designated ST, SB, SS, or SN.

The ST (Shields Terminated) designation indicates that the shield for  
each wire will be terminated only at the jack terminal. Shield wires  
do not interconnect from jack to jack.

The SB (Shields Bussed) designation indicates bussed shields. Each  
row of jacks has a buss bar that connects all shield connections from  
that row together and is brought out with a single ground-wire lead.

The SS (Shields Strapped) designation indicates strapped shields,  
meaning that the shield of each top row output jack is connected to  
the shield of the input jack directly below it. This connection  
remains whether or not patch cables are inserted into the jacks.

The SN (Shields Normalled) designation requires a special patch bay  
using jacks with shield normalling switch contacts. These contacts  
allow the shield to be either half or full normalled from a jack in  
the top row to the jack immediately below it. This is the least  
common of these grounding schemes.

5. Termination The wiring to connect the patch bay to your equipment  
can be done in several ways:

Cables can be pre-wired to the jacks in your patch bay and left blunt  
cut or trimmed and prepped as required.
Connectors can be soldered onto "cable tails" (shielded pair wires  
soldered to the jacks in your patch bay and long enough to reach your  
equipment) for direct connection to your gear. It is possible to  
specify the ground scheme at the equipment connectors. For individual  
XLRs, 1/4", or RCA connectors, the shield is connected to the  
appropriate terminal of the connector. The GL (Ground Lift)  
designation indicates that the shield is left disconnected at the  
connector.
Inline or chassis multipin connectors can be wired to short lengths  
of cable soldered to the jacks in your patch bay. You then connect  
cables between these connectors and your equipment. This arrangement  
allows you to easily remove the patch bay from your system while  
leaving the basic wiring from your equipment to the patch bay intact.
6. Cleaning Whirlwind recommends cleaning patch bays by inserting a  
clean plug five or six times into a jack. The use of chemical  
cleaners or compressed air is not recommended.


Don R. House K9TTY
drhouse at nadcomm.com