Got Buzz? Read This.

We got into a discussion about buzzing single-coil pickups over in the lipstick tube thread. Reader Matthew Seniff chimed in with some well-informed observations and remedies. I’ve moved them here so more folks will see.

Another reader had written: “Every time my kids turn on my kitchen light my amp starts buzzing. It’s due to the rheostat that controls it. It’s old but I’m too lazy to change it.” To which Matthew replied:

Actually it is most likely a poorly designed dimmer switch where the solid-state switch (usually a triac) is not being turned off and on at the zero crossing point of the AC line. It could also be malfunctioning. A rheostat is a big wire wound variable resistor that is too expensive and large for most modern dimmer applications, but which used to be used commercially a great deal before solid-state switches had all the bugs worked out of them. When the solid-state switch turns off at the wrong time, it creates hash, which radiates much like a radio station thru the electrical wiring. This is the same thing that creates noise onstage in bars from the lighting systems that have problems.

It is possible to reduce this problem on single-coils by using copper tape to line the single-coil cavities, or even wrap the sides and bottom of the coil pickup. Lining the control cavity and pickguard on a Strat-type guitar can help reduce hum and noise. This stops electrical fields, but not magnetic fields, which is good, since that would impede string pickup. But it’s bad if the noise was coming from a magnetic source that could still be a problem.

There are also issues with grounding the controls and pickups I have found that establishing one ground centrally in the control cavity and keeping the ground wires short and all near the same length can drastically reduce hum in a guitar. This called a “star ground” system.

Seymour Duncan P90 Phat Cats are single-coils inside steel shells like old Gibson PAFs. This makes them very quiet for P90s, but does make them a tad more controlled-sounding. (I like my P90s to be as mean and snarly as possible, but I do still like the Phat Kats even if they are a bit too “polite.”)

There is also a material called mu-metal that is an alloy of nickel, copper, iron and molybdenum. This is even better than copper, but it also stops magnetic fields, so it can’t be used at the working side of the pickup or it would kill the string signal. If you can find the stuff, it will work wonders. We used to use it on car stereo installs where there was a lot of engine noise in the dash wiring and nothing else worked.

A pickups works like a generator. A changing magnetic field around a coil produces current in the coil of wire. A coil of wire can also act like an antenna for electrical fields, like those produced by poorly designed dimmer switches and lighting controllers that work by having solid-state switches that turn on and off during the AC cycle. When the switches are designed properly, the solid-state switch turns on and off at the zero crossing of the AC wave, creating very little noise. But when they are poorly designed or defective, they turn on and off while there is a voltage present, and that causes spikes to radiate out of the electrical wiring.

My dad had a dimmer like this in his house for many years that I finally replaced with a new $15 dimmer, which solved the noise on all the AM radios, my guitars, and stereos in the house. Florescent lights used to be a big problem as well since the ballasts (which are essentially half a transformer) could produce a lot of electrical noise. Modern fluorescent lights use electronic ballasts that eliminate virtually all noise from them. Neon lights sometimes have very crappy supplies that can produce a lot of noise as well.

Finally there is the problem of RF radiation causing problems usually thru audio rectification of the RF by some electronic components. I won’t try to explain that one since it would just give you a headache but like you say above a good ground and an AC power conditioner with RF suppression built in will usually handle it.

Thanks, Matthew! Now I’m going to replace that 10-year-old dimmer switch in my studio…

3 comments to Got Buzz? Read This.

  • Nick Guetti

    I have a Godin LG SP90 with noise issues. The buzz is hardly noticeable normally, but when I try to add compression (or especially comp & overdrive together) it becomes a screaming nightmare. I’m planning on replacing the bridge P90 with a humbucking soapbar, but the neck tone is so perfect that I can’t do the same thing there. Will a high-quality noise gate work? Or should I invest in a better compressor (mine is a Pigtronix Philosopher’s Tone)?

  • A noise gate might work I recommend the Rocktron Hush systems as they are a 2 prong approach. There is the standard gate that comes on in a slopped fashion. Then there is a second filter which works along with the gate that reduces high frequencies at lower volume levels and opens up the higher frequencies as the strength of the notes increase. This sounds fairly musical and I use the stereo rack units in my system. I use one on the left side going to the input of my Boomerang Looper and run the output of the looper to the right side of the Rocktron Hush. I do not slave them for this but it gives nice clean loops without noisy artifacts. I also use one of these dual rack units on my Maestro Phase Shifter (the one with the big colored teeter toggles that sounds great but has a lot of hiss) I put the left side on the input of the Maestro with very little effect dialed in and I put the Maestro output into the right side section with the gate and the filter set about midway and slave the right side to the left side. This makes the Maestro pretty quiet in between notes in a musical way.
    Does it hum when you take you hands off the strings or even when you are touching the strings?
    You may want to double check the grounding of the bridge and strings on the guitar you can take a clip lead and run it from the output jack nut and touch the strings with the other end. If it gets quieter then you have a bad string ground. You can either leave the clip lead on or fix the ground to the bridge there are also some other safer methods using caps to ground the bridge and strings which can help you not get shocked when you use a mic.. I see this problem on guitars with trems  a lot. I have also seen guitar wiring that accentuates hum by having multiple ground points jumping around the control cavity, it is best to have a main ground point with ground wires radiating out from it to the pots etc. rather than grounds leapfrogging across the cavity. Lining the cavity with copper foil can also help quiet things down as well as copper foil in the pickup cavities, all the pieces of the copper foil should be connected together by soldering and well connected to the main ground point.
    A final alternative is to use a pickup like a Seymour Duncan Phat Kat which has a housing like a PAF humbucker the steel case cancels electrical field noise pretty well but not magnetic field noise if that is an issue. You may also be able to rewire the guitar to have the P90s humbuck when they are both on (although it won’t sound like the neck pickup alone which IMHO is one of the greatest tones ever). There is also a system where you have a dummy coil mounted in the guitar somewhere that doesn’t act a pickup but instead a hum antenna then you can use it’s output to cancel the hum on you pickups with out affecting their tone much if at all.
    Finally just to be sure check all your cables especially your cable from guitar to the FX pedals as there are some that are noisier than others make sure it is not running along side of AC extension cords or speaker cables. You should also use a power strip that has RF suppression just to help keep power line noise and RF out of your system (in fact get one that has a guarantee on it that is insurance for your system being damaged by spikes etc. they don’t cost much more). Also do not use excessively long AC extension cables. It is also possible to pick up hum from your guitar amp so if you have a separate head try rotating it up to 90 degrees or moving it away from where your stand with your guitar. Many times just rotating your guitar can reduce hum pickup standing at a slight angle rather than straight across the stage can look sort of inscrutable (cool like Charlie Chan).
    A compressor is always going to accentuate hum it is just the way it works, the Pigtronix is a good unit I can’t imagine changing it would help much.
    It is also possible to learn to live with some hum by turning down you volume when you aren’t playing etc. and IMHO P90s are worth some hum because they are the coolest pickup known to man!!!

  • joe

    Wow — thanks for even more great info, Matthew! 


    I pity the fool who doesn’t read this.

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