Grounding Essentials

Proper grounding (and shielding) is a vital part of a good sound system. Besides from the fact that it will prevent you and your equipment from electrocution, it will also make less noisy.

The shielding of the equipment is there to prevent interference of the audio signal. With improper shielding you are likely to pickup radio frequencies, noise from mobile telephones and electricity cables. Grounding enables the interference to be flowed away. When this is improper, the interference and static builds up and causes various noises and cracks in your audio signal and might even damage your equipment. So for a noise free and non-lethal guitar setup, proper grounding is essential.

Unfortunately if you have everything grounded, even this can cause annoying hums. These are caused mainly by 4 reasons:
1. the use of more then one outlet for your gear,
2. each piece of gear should only grounded once,
3. different phasing of electricity,
4. adapters.

Sharing one outlet
Let's say you have an amplifier and a 19" rack with various effect processors. If you connect them to a different outlet in the wall, it's possible you get a different ground for each unit. This causes hum. Use just one outlet to power your whole rig, you will need something to distribute the electricity to your gear. Multiple outletstrips are an easy solution. Most rackmount power distribution units also have filtering for cleaner electricity and worth considering.

Grounded once
The 2nd reason for groundloops is more difficult to tackle. To do this properly it may take up a lot of time, but pays off. Simply lifting the ground of the equipment might sometimes seem like a solution. But unless you are really sure what you are doing, this is not a good solution and might even be dangerous. Each piece of equipment should receive ground, one way or another. But you should never be in doubt if it does or doesn't have ground. That's why a step-by-step method of setting up your gear is highly recommended.

Let's assume each piece of gear in the 19" rack and the amplifier has it's ground connected through the mains cable. If you use standard interconnects, each device is connected to ground through it's own mains cable and again through the shield of the interconnect cable connected to each other device with ground. In this case you would need to lift either the ground on the mains cable or the shield of the interconnect.

But with rack devices, chances are high the rackrails it self has ground as well, because one or more units are directly connected to the rails. Using shoulder washers or gadgets like humfree's are an option, but there is an easier way to prevent groundloops in a rack. Lift all the ground of the mains cables of all devices in the rack, except for one. Make sure you strip the paint on the back of the rack ears of each device so you are sure they are directly connected to the rack rails. To be 100% sure, use a mutlimeter to check this. Make sure the devices do not touch each other. If they do, using some gaffa to isolate them is a simple solution.

If you've done the previous, you've done 50% of the groundloop prevention. Next phase is making custom audio cables. For this you would need enough cable, connectors, good solder and solder machine, cable stripper, etc. I would highly recommend using Neutrik connectors as they are superior to most connectors and easy to use. Double core audio cables (microphone) are a good choice to make excellent interconnect cables. Key factor for audio cables is low capacitance (lower then 90pF per meter) and with good shielding qualities.

Disconnect all audio, midi and switching cables. The idea is to work your way back from the speaker to your guitar to find out what's the best way to connect your gear. Some connections work fine with grounded cables, others need interconnects without the ground connected on both sides. Depending on the complexity of your setup, it may take up some time to figure out which cable is need, lifted or normal, for each connection. I prefer to use four long interconnects, two normal and two with the ground lifted. Use these cables to find out which ones you need to connect the devices. When you are sure which type of cable works best, make a custom one which will fit perfectly.

As mentioned before, I recommend using a double core, shielded cable for all connections. Use one core for the tip/audio. The 2nd core is connected to the ground/sleeve of the connector. The shield of the cable is connected only on one side to the ground/sleeve of the connector, the other side if the shield is not connected and completely removed. The shield should be connected to the connector which goes into the "output" of a device. So for a cable between a preamp and a poweramp, the sleeve should be connected on the side which goes into the preamp. The receiving side should not have the shield connected.

Now there's another point of where the ground of the devices could be connected together: when you use a switching unit to change the channels of your preamp(s), turn the fx on/off, etc. With a unit such as the Rockman Octopus, the ground of switching outputs are connected together and can therefor cause groundloops. With a more sophisticated switcher, such as the Nobels MS-8, the grounds have galvanic isolation or other solutions to prevent groundloops.

Difference in phase
If you want to learn more about this subject, download the following document. In a nut shell it explains how difference in phases can cause noise in your system. So by simple turning your mains connector around, it can reduce hum. I know for a lot of people this may seem unlikely, but the difference is there. Read the article if you want to know the scientific background.

Mains cables consist out of a green/yellow wire which is used to connect the ground. The blue wire should be neutral and the brown one the hot. Most amps and rack gear have 3 pin euro mains connectors. If the device is built correctly, the bottom left pin on a male connector should be connected to the hot/brown wire of the transformer. If you use a 19" rackmount powersupply it highly recommended to make custom cables to your preferred length and make sure all cables are wired the exact same way and with the hot wired to the brown cable. Of course you would first have to check the polarity of your mains outlet and be sure that your powersupply is connected correctly. I have marked my mains plug so I know which side of the connector should be hot and which should be neutral. I simply check the outlet to see what the polarity is and provide my setup with the right power.

In all cases use stabilized adapters with more then enough power. Adapters may cause noise when they are close to your pedals (wah!) and/or cables, so try to keep them at least 1 feet away from each other. As mentioned in the previous paragraph, the phase of an outlet can have an influence on your noise ratio.

All in all reducing hum and noise can be really tricky and hard to solve and can take up hours and hours. But if you care about your gear and tone, take some time and do your best to get the maximum result with your gear. Even with a few simple adjustments, big improvements can be made.

When using a rack setup even where a piece of gear is placed inside the rack can have influence on the amount of hum. Power supplies and poweramps close to wireless units can cause hum for example. So it's wise to plan ahead before setting up your rack system. More on this in the AFFECTIVE RACK SETUPS article.