Rack Grounding, Buzzing and Cable

Pictures soon

I was recently tuning up my rack in the shop and wanted to offer a few tips if you are experiencing buzz and hum from your rig- whether it is a rack, pedals or a combination.

In my case I have a few pedals and a rack with an old Rocktron Chameleon, a BBE maximizer, a Layla recorder, an Alesis Mixer, an Alesis QSR and a Behringher V-Verb Pro. This is fed by an AB switch selecting either the rack to the amp or the pedals to the amp.

pic here

I recently built myself a fine rack for all this stuff and it created another problem. Ground Loops.

Before starting keep in mind that eliminating 60hz noise and buzz is a matter of degree. It is a fact of wiring and you should be able to get rid of 95% of it but some will always exist. At mid volumes you shouldn’t hear any or very little. It you crank your tube amp to 11 you are still going to hear noise no matter what you do. Solid state amps are a little better but noise is noise and at high amplification or gain levels you are going to have some, period.

Primarily the rack setup was injecting 60hz noise into everything because of ground loops between all the units. These loops occur because of an imbalance between the rack units’ ground in relation to other units mounted on the same rails, thereby electrically connecting them to each other. The first thing to do was to isolate each rack unit from the rails breaking the ground loops between the units. To do this you can get a product called Hum Free rack tabs that are very good and I recommend them or you can accomplish the same thing with electrical tape and a surgical rubber spacer or some kind of homemade plastic spacer, which is what I did. It’s more efficient to just buy the rack tabs but it was Sunday night and I wanted to get it done and not wait a week for an order to arrive. And I had other things to do.

Here is how I did it -(see the pics above). Put electrical tape on the back of each rack tab and cut out the holes with a razor. Then cut a piece of surgical tubing and slip it over the rack screw. Your rack screws should have plastic washers on them already. Then screw the unit back in. That little washer you made should go into the rack mounting hole and insulate the rack unit from the screw. The tape keeps the unit from touching the rail. You may have to put tape on top and bottom of the unit case somewhere to keep the cases from touching each other. You would have to do that if you used the Hum Free tabs. That’s why some people complain that the Hum Free tabs don’t work. It is because the units are still touching each other by their cases somewhere and they don’t know any better. This touching is where rack rash comes from. You have to totally isolate each rack unit from any other rack unit. It’s not hard, just a pain in the arse. If you have an ohm meter, unplug everything while you are doing this and measure the unit case to both rails as you mount it. Make sure you have an open circuit and no shorts between the unit and either rail. If you don’t have an ohm meter just do a good job and chances are it will be OK.

Next and this is very important, and this whole topic can be full of BS if it is allowed. I will avoid that. You want to make sure you have real good cables and well soldered phone plugs. I had some Audio Technia cables that were noisy as could be and I replaced all of them. Who would have thought, right? I had some Hosa cable that shielded so well you couldn’t hear it. Who would have thought, right? So don’t buy cable by the name. Find a brand you like and use it. Some cables shield 60hz and RF much better than others. I don’t believe in boutique cable. I’ve even been told of a cryogenically treated power cord. My waders are not high enough to keep from drowning in this BS. I’ve been around long enough to know that 90% of this kind of stuff is total BS. The only thing that should ever be cryogenically treated is your beer. And all decent copper is oxygen free. More marketing hype. I have cable in my refrigerator waiting for those who will pay me 3 bucks a foot. If you pay over $1.00 a foot for guitar cable you should just set your money on fire since that is a quicker way to burn it. There are a few exceptions in the capacitance of the cable in relation to tone but that is another issue for another discussion. Most all guitar cable is going to fall into the 30pf to 45pf per foot range. You are going to pay more for 20 something pf from the boutique marketers, a lot more sometimes and it is going to make your tone brighter until you load it back down with other junk you plug into and you end up where you started, but with more expensive cable. If that is what you want, go for it. Just make sure you get well shielded cable on the order of 97% to 99% braid. Hendrix recorded with the common stuff and played live with it. Beldon makes it and Hosa uses it sometimes as well as any number of manufacturers. Do what you want- just use good cable with good terminations. If you suspect a noisy cable just swap it out with another known good one to test and if it is noisy throw it away or it will sneak back into your chain one day. A couple of Beldon cables you can use in bulk are 9778 and or 8218. The 9778 is a bigger more flexible cable, the kind you are used to and the 8218 is like the George L cable that is over hyped. But there are others. Just look around. Look at the data sheets for the two cables mentioned, easily found on the web and you will learn about cable.

One more big thing about cable. Keep signal lines away from power lines. If they have to cross, and they will, cross them at 90 degrees to each other. If you place a signal cable next to a power cable or close to the power supply inside a rack case you will have hum.

Always remember that tone starts in your head to begin with and everything else is connected further down the chain. And sometimes when you mis-wire things tone travels right through your wallet, most wallets do not have a true bypass switch and your tone and bank account will get reduced so be careful with it.

Now, once you have done all of that and things are still buzzing you might need to further isolate certain rack units from the common ground. You can do that with a three prong to two prong adapter. The same thing your grandmother used to connect a hundred xmas light strings to one outlet. Or you can do what I did and cut off the ground prong on a power strip. This could kill you so it is just used to find the noisy rack unit. Then you have to do something else so do not leave it plugged up this way or you may regret it.

Ground Isolator

Plug this power strip into your normal rack power and one at a time plug each rack unit into this ungrounded power strip and see how noisy things are. You may find that one of the rack units is contributing noise when it is connected to the common ground. In my case it was the Behringher reverb unit. (Okay, I can hear it now, you should have known Behringher is junk etc, etc, etc.) We’ll I’ll have you know this unit worked well for a long time and now it is junk so I got my money out of it.

So if you find this is a problem what do you do? You can buy a thing called a Hum X that will isolate a unit from others and that is about it. Or I’ll show you how to make one (see below) but if you kill yourself it is not my fault. That is my disclaimer. In my case I quit using the reverb unit because I didn’t like it anyway. But don’t leave the noisy unit plugged into the ungrounded power strip as it could cause your electrocution if something goes wrong.

There are no mysteries to noise and buzz, just things you have to do. I still have a few cables to replace but the rack and pedals are quiet as can be. Now If I crank up my super duper over drive it buzzes horribly like it should but that is amplified noise and not the same as 60hz hum and fizz. For overdrive noise you need a noise gate and or a noise reduction system like an ISP or Hush unit or similar. Better yet if you fix all your cables and grounds and manage your gain levels you may not need any noise gates or reduction units in your studio!

Good Luck.

2017-07-23T09:40:12+00:00