PATCHED IN
Jul 1, 1998 12:00 PM,
Jim Hoffman
Patchbays are like a good pet. Whether it is a golden retriever or agoldfish, proper care for your pet not only keeps it healthy, but it alsogives you years of satisfaction and enjoyment. The same can be said foryour patchbay. Although a properly maintained patchbay may not necessarilybring enjoyment, at least it will not be a source of constant headaches,and that should generate some joy. Simply put, keep it well maintained andit will work as it should.
Before we get into the details of proper maintenance, let’s review thephysical construction of a patchbay. This will help in understanding bothhow they work and the critical areas where common failures can occur. Apatchbay starts with a piece of aluminum or thermoplastic encased inaluminum. If it is an audio patchbay, it is required to be 19 inches (483mm) long, or at least fit into a 19 inch (483 mm) rack. Mounted into theframework, isolated from each other and the patchbay frame, are the jacksthemselves.
Depending on the style, either 48 MT or 1/4 inch (6 mm) style jacks, or 96TT or bantam-style jacks are used. MT jacks and TT jacks are for the mostpart similar, except for their physical size. The 1/4 inch (6 mm) jack willhave a bushing or sleeve ID to accommodate 1/4 inch (6 mm) mil-type plugsor patchcords, and the TT version will have an ID that will accommodateplugs or patchcords with a 0.173 inch (4 mm) OD. There are some patchbaysmanufactured that require 1/4 inch (6 mm) commercial plugs, but becausetheir primary market is the musical instrument (MI) market, they will notbe discussed in great detail here. If you are not sure what kind ofpatchbay you are dealing with, the easiest way to differentiate a 1/4 inch(6 mm) mil-spec patchbay from a 1/4 inch (6 mm) commercial-style patchbayis to look at the bushings of the jacks in the panel. Most MI patchbays usejacks that have a threaded bushing and nut. They also have the same styleof jacks mounted in the back of the bay. Mil-spec patchbays have a smoothbushing mounted flush with the panel. Another option is to look at thepatchcords, specifically the tips of the plugs. The commercial version willhave a pear- or spade-shaped tip, while the mil-style version will have arounded or bulb-shaped tip. Do not mix and match the two, because they werenot designed to intermate. The tips of each plug were designed to matespecifically with the corresponding jack tip springs. Using one style withanother will eventually cause major intermittancy problems.
The final part of a patchbay is the method of terminating the input/outputcables to the jacks. Some popular methods include IDC terminals, multipinconnectors (like EDAC or ELCO styles) and plain old solder terminals.Depending on the type of patchbay, other bells and whistles can includecable trays or tie bars, rear support bars and slide-out trays. From amaintenance standpoint, the three most critical areas of a patchbay’slongevity are the springs in the jacks, the contacts between the jacksprings and the terminations to the cable input/outputs. Let’s go intodetail of each critical area, starting with a detailed overview of the jackitself.
Most jacks used in audio patchbays consist of some sort of frame, a groupof springs that mate with the plug, contacts that actually make and breakthe circuits and a device to hold everything together. There are threebasic types of jack frames-plastic, zinc diecast and welded and formedsteel. Plastic jacks are the most cost efficient because plastic materialtends to be cheaper than zinc diecast or steel, but plastic jacks tend towear down quicker, leading to intermittancy problems. They also are moredifficult to replace because they are usually soldered to a PC board. Youhave to either desolder the jack from the PC board or replace the completemodule itself. Diecast frame jacks are more expensive than plastic, butcheaper than steel. Although more durable than plastic, they are not asdurable as steel. Diecast material can take a set, that is, if a plugremains in the jack for any length of time, the diecast will try tocompensate for the load caused by the inserted plug and bend to conform toit. This actually deforms the jack frame and causes the jack to becomeintermittent. Steel, although more costly than the other options, isusually the most rugged. Even under constant load from a plug, the framewill not bend. Gussets are usually added to the frame to provide morerigidity.
Inside the framework of the jack are the springs. In plastic jacks, formedwire makes up the springs. In diecast or steel frame jacks, a leaf springis used, usually a nickel-silver alloy. The springs are physically moved bythe insertion and withdrawal of the mating plug which, in turn, opens orcloses contacts attached to the springs. Formed wire springs act as thephysical contacts between the springs; leaf springs use either a welded-oncontact or a bump formed onto the spring during the stamping process.Welded-on contacts are usually made of palladium or gold alloy, with goldalloy offering lower contact resistance. Formed contacts are usually madeof the same material as the leaf spring itself, though the area of theformed contact can be plated with another material. Plastic jacks use thehousing itself to hold the wire-form springs together, while themetal-frame jacks use tubular insulators and screws to hold everythingtogether.
Audio signals pass through the jacks at two points-where the plugsphysically touch the jacks at the springs and where the contacts are openedand closed by the mating plug. In a three-conductor or TRS configuration,the plug finger mates with the jack at the tip spring, the ring spring andthe sleeve or bushing of the jack. The signals also pass through the areawhere the contacts open and close. Therefore, it is vital that these twoareas in the jack remain as clean as possible if a reliable signal is topass through.
The first plan of attack in keeping these areas clean is to minimize thedust or contaminants in the adjacent areas. Many studio environments useair filtration systems to clean the air, removing dust and unwantedparticles on a constant basis. This keeps not only the patchbays clean, butalso all of the other audio equipment in the area. Using a patchbay with acover also helps because it keeps some of the dust off the jack assemblies.It may not be the complete answer, but it certainly does not hurt.
Given the fact that many patchbays are installed in areas where dust andcontaminants are part of everyday reality and cannot be kept to a minimum,proper cleaning of the critical areas becomes even more important. Regularinsertion and withdrawal of the plugs on the patchcords physically removesa lot of the common build-up found on the area where the leaf springs andjack bushing mate with the patchcord plugs. Doing this on a scheduled basiswill decrease the risk of contamination and minimize problems in thefuture. Using plugs or patchcords with nickel-plated plug fingers alsominimizes build-up on leaf springs and plug fingers. Use a common lint-freecloth to wipe the plug fingers clean. Again, do this on a regularlyscheduled basis. Avoid such tools as burnishers because they take materialaway from the leaf spring in their cleaning process. Burrs can be left onthe surface of the leaf springs, which causes grooves in the mating plugs.Like a virus, one damaged plug gone unnoticed can cause problems with everyjack in which it is inserted.
The contact area of a jack is more difficult to keep clean because it ismore difficult to access. Options for cleaning contacts include pressurizedair or solvents injected into the jack through dummy plugs. The dummy plugsare plastic models of the plugs, except they have a hole running the lengthof the plug. The plug is inserted into the jack, and using a long nozzle,the compressed product can be injected into the now open contacts. Theconcept is that with the contacts now open, the air or solvent canthoroughly clean the contact area. A caveat with this method is that theair can actually stir things up inside the patchbay and create more havocwith dust, or the solvents can actually attract more dust onto the contactsthemselves. In either case, you may be causing more problems than what youstarted with. The most reliable method is to use jacks that have cross barcontacts. Cross bar contacts are contacts on the sides of the leaf springthat face each other in a cross configuration. One contact runsperpendicular to the leaf spring, the other parallel. As the leaf springsmove, the contacts ride back and forth against each other, wiping thesurface clean with each insertion and withdrawal. Adding gold alloy to thecontacts also reduces contact resistance, thereby increasing reliability.
The last area that needs to be maintained is the area where the wires fromyour inputs and outputs are connected to the jacks. As previouslydiscussed, the main methods are IDC terminals, multipin connectors andsolder joints. The most important thing to do in this area is to keep theweight of the cabling off the terminations. Stress caused by the weight ofthe cables can loosen IDC terminations, break the wires away from thecrimps of the multipins and crack even the best solder joints. The bestmethod is to buy a patchbay with a good cable tie bar or cable tray or riga homemade system to do it yourself. Either case, keep as much weight aspossible off the back of the jacks. If you decide that you might be betteroff replacing your old patchbay, you could not ask for a better time to buyone. There are plenty of options available on the market today that werenot there even five years ago.
The patchbay industry offers just about every conceivable option to helpwith installation and everyday use. The more basic patchbays are those thatconsist of the patchbay frame with pre-loaded jacks, with the jacks havingsolder terminals on the back. These basic panels usually have either acable tie bar or cable tray on the back, and either will take the weight ofthe cabling off the back of the jacks. The typical resale price is around$200 for the 1/4 inch (6 mm) style with 48 jacks and $300 for the TT stylewith 96 jacks. Most will be available with full normals, half normals, orno normals. The full normal versions are a little more expensive comparedto the half- and non-normalled versions, but they offer much moreflexibility down the road. Look for a patchbay with large designationstrips, because they are much easier to read at a distance. With solderterminals on the back, you will have to solder your connections on the backof these bays. Although labor intensive, these are the most bullet-proofbays made for those of you who believe strongly in solder joints.
The next level are those bays that require some sort of connector orpush-and-poke interconnect. In this case, the manufacturer has done thewiring internally, and has brought back the rear-jack terminations tosomething other than a solder joint. Options include EDAC or Elco-typeconnectors on the back. In this case, they provide the panel mount side,you will have to provide the end that will connect to your cabling. Thewiring is done to a standard wiring code. The installer needs to terminatethe mating plug, using a wire crimper and the terminals themselves. Withthe poke- and-hold, the wires are stripped and loaded into thepoke-and-hold terminals. Because a lot of the labor is done by themanufacturer, the cost of these patchbays increases (typically around $800to $1,000 for a 96-jack unit), but your labor is decreased. Someone veryadept with a wire stripper or crimper can easily wire up this style ofpatchbay. One advantage of the EDAC or Elco-type of termination is thatthere are companies that offer pre-made interface cables that you simplyplug into the back of your patchbay and right into your equipment. Whenlooking into this style of patchbay, again, look for large designationstrips. Also look for the ruggedness of the chassis; make sure heavy-gaugematerials were used throughout.
A final option, most popular in the broadcast industry, is the IDC type oftermination. In this case, a punchdown tool is used to terminate the innerconductors of the cables to the IDC terminals provided on the back of thepatchbay. Line up the wires with the terminal, and a quick punch down doesthe terminating. A proficient installer can wire up this type of bay in notime at all. IDCs have become extremely reliable and provide gas-tightterminations, so there is no worry about the connection failing. Again, thekey is to keep the weight of the cabling off the terminals. Mostmanufacturers provide more than adequate cable tie bars to accomplish this.Patchbays in this area typically run from about $900 for a 48- jack unit toabout $1,300 for a 96-jack unit. More labor for the manufacturer, but lessfor the installer.
One of the more interesting options available with this style is theslide-out tray. In this case, the unit is essentially built onto aslide-out tray, which allows easy access to the termination points from thefront of the rack. There is never a need to get behind the rack tore-configure the patchbay. Most versions have a captive screw design, whichlocks the unit into its normal position. When the bay needs to be rewired,unscrew the captive screws and slide the unit out. Because the IDCs aremounted horizontally instead of vertically, space is saved, and theterminals are easily punched down instead of from a vertical plane. Theunits typically run about $1,400 for the 96-jack units, but keep in mindthey do save space and labor.
There’s an option to fit every need you may have and your abilities with asoldering gun or crimper. With the right unit and proper maintenance, theleast of your headaches should be your patchbay.
Many professionals never think about the importance of connectors. Mosttake it for granted that all connectors are created equal with littlepractical differences. Nothing could be further from the truth. Connectorsare a vital part of any installation and should be chosen with great carebased upon the application. I have installed high-end home theaters forpeople who balk at spending $4 per connector when the line quadrupler intheir system costs $25,000. Connectors are just not a priority purchase inthe mind of most installers and are often last on the minds of clients.
To convince them of the importance of the connector in their systems, Ioften use the car mechanic analogy with my clients by saying, “Look, I amthe guy doing the engine, making sure the performance of your system isperfect. I know that if I were doing the leather interior and the paintjob, it would be an easy decision for you to make when it comes to qualitycomponents and budget. You have got to go with the highest quality cableand connectors so that the car always runs great and not just looks great.”
Most clients are satisfied with that, and as long as I include a guarantee,they will let me use superior parts. This saves everybody time and moneyand ensures the project will operate as expected over the long term.
Remember that when a job presents itself, carefully select the quality ofconnectors and the type of connectors best suited for the installation.There are so many types of connectors-instrument-style,panel-mount,L-shaped, locking-jacked and many more. There is always the right connectorfor any given job, and it should always be the only choice.
When using cable to connect audio and video devices, remember that thecable is only as good as its connectors. I choose connectors for each jobbased on several factors-budget, performance, physical characteristics andconnector style. Each situation is different and therefore requires ananalysis of each aspect of the requirements based on the needs of theclient. I wired a professional recording studio for a client where hewanted the best of everything. The studio’s needs were high end, and theclientele was equally as impressive. Another twist was that the studio waslocated directly next to the ocean in a very humid environment. Simply put,corrosion was a factor given the physical environment.
Those of you who have wired 500 or more connectors for one small job aloneunderstand the need for the connectors to be easy to work with as cablesare soldered and fabricated over the course of weeks or even months. Solderjoints are also critical, and proper preparation of the cable and connectorends must occur if the solder joint is to hold over time. The contact endof the connector has to be both rugged and properly molded to insure agreat connection.
Regardless of the cable you choose, everyone could use more information onthe myriad of choices in connector technology. Be sure to contact yourconnector manufacturer before your next job if you need any advice or haveany questions.
