Building a new Rack?

Hello Everyone,

   Harley Hexxe here. I've been a long time ADA devotee, and building racks since 1987. Along the way, I've encountered all sorts of various problems that are associated with building a rack and using equipment from different manufacturers. One of the most common problems associated with building any rack is ground loop hum. By taking your time, and a little planning in advance, you can eliminate this problem from the rack and your pedalboard as the source right from the start. Keep in mind also, that before you build your "Rack of Doom," that the more you add to your rack, and the bigger you make it, the more you are opening yourself up for ground loop hum.
   At the suggestion of one of the Moderators, I'm posting this thread as a reference for all of the Forum Members.

   For the first-time rack builders, you will need the following:

   * One, or two rolls of standard 3/4" electrical tape.
   * #1 Phillips screwdriver. (#1 phillips bit in a low-speed rechargable driver is good, but I do NOT recommend using a drill, as they tend to strip the Phillips heads.)
   * Exacto knife, or some other very sharp blade with a small tip.
   * Good quality rack mounting screw kits, with nylon isolation washers.
   * Zip strips, or wire ties, or even plastic flexible conduit.
   * A good quality power conditioner/supply module.

   After you have decided on all of the 'must have' units to use in your rack, and have picked out the appropriate size rack to suit your needs, then it's time to assemble and wire up your rack.
* When I am assembling my rack(s), I always leave the back cover on and lay the case on it's back with the mounting rails facing upwards. This allows me to place each unit in it's correct slot, and it also lets me see if the rack ears can be centered without touching any metal surfaces. (Some rack cases have aluminum frames around the rack opening. this looks cool, but can work against you if your rack gear makes contact with it.) Before placing the unit in it's slot, begin applying the electrical tape to the mounting rails, and use the Exacto knife to trim the tape off the screw holes in the rails. Discard the hole centers. Doing this will help prevent the screws from going in crookrd, and cross-threading. I use two rolls of electrical tape at the same time so I can do both rails simultaneously, and have a single constant strip one each side from top to bottom. I know this is a bit tedious, but it's cost-effective, and it works. After placing the tape on the first rack unit slot, place the unit on the tape and put in the rack mount screws, but only snug them in lightly for now. Take the tape that is coming from under this unit, and create a small fold that will rest between this unit, and the next unit to go in. Repeat this step with each unit all the way down the rack. If you are planning to leave a rack space in between each unit, then skip this last part.
* Apply electrical tape ( as needed ), to the underside of the rack panle faceplate, to prevent it from coming in contact with the next unit below it.
* Apply the small rubber feet with adhesive backing to the bottom of your rack unit where it may come in contact with the next unit below it.
*** These last two steps may also be eliminated if you are leaving space between rack units, BUT, if you are going to put blank rack panels or vented rack panels to cover the open slots, you will need to use the electrical tape to isolate them from each other! ***
* Run all power cables together, and to the left side of the rack, since most rack equipment will have the power cables on that side. Some manufacturers have theirs on the right side (Rane *GRRR*). Rack units that are powered with AC adapters should have the power cable tucked between rack units and run to the left side of the rack, and the excess cable can be grouped with the other AC cables and tucked in the area on the left side of the rack. For rack gear that has the AC cable on the right side, do this same thing in order to keep these power cables from getting any closer to the audio signal cables. Secure the power cables together with the Zip Strips, or flexible conduit, and tuck into the space on the left side. AC Adapters should be mounted on the left side inner wall of the rack. I like using Dr.Ferd's Wall-Wart Removers for this, but you may find similar plug adapters at Musician's Friend, or AMS. These can be mounted with a small wood screw to the inner wall of the rack case. For SKB, and other molded rack cases, use clear silicon caulk to mount them, just make sure you mount them close enough to the power suppy to plug them in.
* Run all audio signal cables together and whenever possible tucked into the right side of the rack. These may also be secured with Zip Strips or conduit.
* NEVER run audio and power cables parallel to each other! In situations where power and audio cables are oriented in such a way that they must be in close proximity to each other, always set them up where they will intersect each other and be in a perpendicular orientation. This will minimize the interference field.
* Control cables ( MIDI, Footswitch, etc.) can be run up the center of the rack and are not affected ( in general), by either power or audio. If you feel you want to run the control cables to one side, I recommend the power cable side.
* I recommend that all power to the rack, amplification systems be supplied from the same AC source. If you have your rack plugged into one outlet, and your rack, or pedalboard into a different outlet across the room, you MAY be on two different household circuts and this can cause hum.
* For all those who use phantom power, (recommended), to your MIDI controllers, DO NOT run your MIDI cable parallel to your audio signal cables going to and from your rack. These MIDI cables are now charged with an active and constant DC power supply. Run these cables separate from your audio lines, and once again when they are in close proximity, situate them to intersect each other, rather than along side each other.
* Never coil excess cables regardless if they are Audio, AC, or DC. Coiling your cables creates an inductance field, and this will create a hum. Always snake all cables to their full length to avoid this, Would'nt it be ridiculous if you tore apart your rack to track down a hum issue, only to discover later, that it was from something like this?

   *** I always recommend a good quality power conditioner and supply module ( Juice Goose, Furman, etc.), not only to help eliminate hum and RF interference, but also to protect your rack from spikes and poorly grounded electrical sources at different venues that you may be taking your rack to. When using one of these units, and wiring up your rack, I recommend doing the power cables first and if you mount this unit at the top of your rack, you may snake your power cables over the top of this and into the plug outlet. Just remember to keep the audio cables away from the top of the rack. This will also allow you to unravel your power cables and avoid coiling them. ***

   *** Following these tips is not a guarantee that hum will be removed from your rack entirely. This does guarantee that you will be isolated from ground loop hum, and that any hum is not because of the way your rack is wired or connected to your remote controller(s). As I stated at the beginning of this post, the bigger your rack is, the more susceptible it is to a source of hum. This is especially true when using components from several different manufacturers. ***


   Good Luck, and I hope that prospective rack-builders find this information useful.



      Harley Cool