Radio studios involve quite a bit of wiring. Runs between the console and equipment are pretty straightforward, from whatever the connector required for the equipment to whatever the connector required for the console. When it comes to trunk runs between the rack room and the studio, however, some type of terminating block is required.
This particular cabling installation is for low-level signaling, contact closures, and the like. It uses a Belden cable with 37 un-twisted wires which do not follow the standard Western Electric color code. The color code can be found here. If it were audio or data, the wires would be terminated differently. That color code can be found here. For more information on color codes and pinouts, see this post.
Many engineers use the venerable 66 block or M block insulation displacement termination. These terminal blocks were designed by ATT to terminate 25 pair 22 through 26 gauge solid wire. The original design was rated for category 3 (16 MHz or 10 mb/s) communications standards. Newer designs are category 5 or 5e compliant (350 MHz or 100 mb/s). Notice the part about the solid wire. Most audio wire is stranded and as such, the metal fingers on a 66 block will cause stranded wire to spread out losing contact with the terminating finger. This causes intermittent connections and audio dropouts, which I have experienced often (before I knew better, I used 66 blocks when building studios). The way to cure audio dropouts on a 66 block is to heat the termination fingers with a soldering iron. This melts the wire insulation and gets it out of the way. In the long run, it is better to use more suitable terminations.
The 110 block is an updated version of the punch block for high-speed networks. it is also designed for 22 through 26 gauge solid wire. This is the termination used on category 5, 5e, 6 patch panels and RJ-45 jacks. They are also formed into block-type terminations the size of small 66 blocks. The 110 block is designed for 500 MHz (1 gb/s) or greater bandwidth. Krone makes a version of a 110 block called LSA-PLUS which is an acronym that stands for: Lötfrei, Schraubfrei, Abisolierfrei, Preiswert, Leicht zu handhaben, Universell anwendbar, Sicher und schnell. This translates to: no solder, no use of screws, no insulation removal, cost-effective, easy to use, universal application, secure and fast. Unlike a standard 110 block, the Krone block is designed for solid or stranded wire. 110 blocks are acceptable for use with AES/EBU digital audio at sample rates greater than 268 KHz as well as gigabit networks and analog audio.
In very old installations, I have seen Christmas trees. This is a wire wrap system where wires are wrapped around metal fingers that form the shape of a pine tree, hence the name. They were very popular in the fifties and sixties and only work with solid wire. It is also time-consuming work and requires special tools and skills. Wire wrapping is a bit of a lost art.
Screw barrier strips have been used to terminate audio cables from time to time. I wouldn’t consider this method because it is too time-consuming, takes up too much space, and is difficult to label.
ADC makes a good termination block called ICON (Integrated Cable Organization Network) which uses QCP (Quick Connect Panel) connectors. the connectors are small square devices that are insulation displacement termination (like 66 and 110 blocks) but require a special tool to “punch down.” This particular type of connector is well suited for stranded wire from 22 through 26 AWG. QCP connectors are also used on some of ADC’s patch panels and other audio products. Like any other termination technology, they are only as good as the person punching down the wires. QCP connections are small high-density devices, I have seen them get mangled by someone in a hurry who got his punch-down tool across two of the terminals by accident. ICON blocks can be used for digital audio, however, they do not maintain the 110 ohms impedance of most digital-type audio cables (neither do XLR connectors, by the way). This can lead to some return loss, which on longer cable runs can cause problems.
Radio systems prefer RJ-45 connectors with Category 5 cable, something they call Studio Hub. These are 110 blocks as noted above, but designed primarily for computer networks. Radio Systems discovered that the impedance of most audio cables is very close to that of computer network cables, audio cable is designed for 110-ohm impedance vs. computer network cable which is designed for 100-ohm impedance. Therefore, RJ-45 connectors and shielded or unshielded twisted pair work well with balanced professional audio, either analog or digital.
For analog audio wires, ICON blocks seem to be the best, most secure high-density termination system. In all my years of using them, I have never had a connection go bad. 110 block and other category 5 or 5e systems also work well. For digital audio, Krone blocks or 110 blocks need to be used in order to maintain the full bandwidth characteristics of the cable being used. Using appropriate cable and or terminations in digital audio circuits often leads to impedance mismatches and high return losses in the system.
