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My brother has an electric guitar which he has not played or even touched for at least fifteen years. It's a cheap strat-like guitar, equipped with three unknown (most likely stock) single coil pickups. Last weekend I was visiting him and he gave it to me.

When I got home, I plugged it into my amplifier and it started to make a very loud buzzing noise. I noticed that the noise is significantly reduced whenever I touch some metal parts, such as the bridge or the input jack. As suggested by this question and many other references that I have found during a quick research, this scenario suggests grounding issues.

A quick note: I have been playing guitar for many years now, but I never tried to fix the problems of any of my guitars - I have always handed them to professionals. Since this is a cheap and old guitar, I figured this would be a great opportunity to learn a bit of guitar electronics and maintenance.

So yesterday I opened the guitar and worked on it a bit. Many components were oxidized; so, apart from checking and resoldering the ground wiring, I replaced the following components with brand new ones:

  • All three potentiometers
  • The input jack
  • Every wire except the ones that come from the pickups

Still, the guitar is making a loud noise when plugged into an amplifier. I really don't think it's just a single coil hum, since it is way too loud even if the volume on the amplifier is low. Also, from what I have read in the past few days, the fact that touching metal parts basically cuts off the noise seems to suggest this is indeed a grounding issue.

I took the time to analyze the guitar wiring and made this simple diagram:

enter image description here

Is the wiring correct? While searching on the internet, I didn't find a guitar wiring diagram that looks like this one. Since I don't know much of electronics, I'm not sure if this guitar was already wrongly wired/grounded.

And in case the wiring is correct, what else could be causing the loud noise?

  • Are you getting ONLY noise, or is guitar signal coming through also? Most likely you have a cold solder joint somewhere, or possibly something touching where it shouldn't. Retouch all the solder points and check that the signal pins on the pots aren't touching the casing or other wire points. – Alphonso Balvenie Mar 6 '18 at 19:40
  • Hi, thanks for your comment. There is also guitar signal, not only noise. I resoldered the entire ground wiring yesterday and checked it again today with a multimeter - it all seems to be OK. Your second suggestion seems very plausible, I'll give it a try later. I have noticed the cavities on this guitar are somewhat tight. Maybe there's some extra touching going on. – Renato Mar 6 '18 at 21:15
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When you have a hum or buzz that is eliminated or affected by touching a metal part of the guitar, this is most likely caused by a grounding issue. On a guitar that has not had electricity run through its circuit in 15+ years I could see one or more exposed wires and/or solder joints degrading due to oxidation.

The remaining hum could come for several sources:

  • Single coil pickups will by their very nature pickup 60Hz hum (And it’s harmonics). This is a type of inducted noise.
  • Electical noise from dimmers, fluorescent lights, A/Cs and compressors (just to name a few sources) as well as RF frequencies in the environment are another type of inducted noise that pickups or
    tube amps can receive and inject into your tone chain
  • The higher your gain setting, the more sensitive your rig becomes to inducted noise. Even humbuckers will pick up inductive noise especially under very high gain scenarios.
  • Conducted noise sources include things like ground loops, noise that enters the system trough a noisy power source and noise added by components in your signal chain

Using a multi-meter with a continuity test function you should be able to easily track down any grounding problem within the guitar itself.

As for the rest of the noise, this is tougher.

First, if a guitar is not shielded, noise can enter through the pickups and the wiring, pots and switches in the control cavity. Your guitar is essentially a giant electro-harmonics antennae. Shielding the control cavity can provide a good amount of noise reduction. Shielding pickup cavities can provide a small amount of reduction but is far less impactful than shielding the control cavity. If the only wire in your tremolo cavity is a ground wire, shielding the tremolo cavity will have no effect. ALL SHIELDING MUST HAVE CONTINUITY TO GROUND IN ORDER FOR THE SHIELDING TO WORK.

Next, getting a good noise suppressor will help. Note I said suppressor not gate. There is a difference. Noise suppressors include both a gate and a filter whereas a noise gate only includes the gate. A good 2 connection suppressor will take a lot of inducted noise out of your tone. Examples of good noise suppressor include the Boss NS2 and my personal favorite the ISP Decimator G String. The only Decimator you want is one of the G series... either G string for a pedal or Pro Rack G for rack. You need to go through the noise suppressor to your amp input, then connect it into your amps effect loop. This will make a big difference in the inducted noise in your signal.

Next for conducted noise get a good power conditioner for your effects and peripherals. You should not connect your amp to a power conditioner. Modern amps exhibit variable power consumption which a power conditioner may have problems with. For the amp, there are ground isolators like the HummX or one made by Logsdon (cannot remember the name). If you want to go really crazy there are isolation transformers like those used for sensitive medical equipment. These are expensive and heavy.

Never, ever use a ground lift as a permanent solution to grounding problems! You are playing Russian Roulette if you do. Ground lifts are fine for diagnosing problems, but they are not a permanent solution!

How far you want to go is your own personal choice. I think at minimum you need to deal with the grounding on the guitar. Especially if your other instruments do not exhibit such a glaring noise problem. A poorly grounded guitar is unsafe and could lead to serious injury or even death. You do not want to act as the ground for part of your system! The further you go with the steps outline above, the more you will tame the noise in your rig.

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It is very easy to see if it is, if fact, from the single coil pickups. Does the hum diminish in the 2nd and 4th switch positions when the two single coils on are humbucking? If yes, it IS the single coil pickups. Get some noiseless (stacked humbucking single coils) OR just use the 2nd and 4th positions and don't go above 6 or so on your tone knobs. oh yea, almost forgot, I also use a passive two channel "hum eliminator" and I use both channels in series (floor effects to input channel one, out to input channel two, then out to the amp. Simple cheap add to the signal chain to reduce hum. It is just velcro'd on the back of my amp.

I have tried the conductive shielding lining of the cavity and I am not convinced that it is effective. I have learned that quality cables DO make a big difference. A cheaper quality cable may work with another guitar fine but may introduce grounding issues with this one. Try that. Also, try other rooms and outlets and make sure you use one outlet for your effects and your amp as to not create any unwanted loops. My guess is that you will eliminate everything else and be back to the noisy cheap single coil pickups in there.

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I've read the answers above and noticed one glaring omission. All answers are focused on the guitar itself. However, the grounding process also includes the guitar cable and amplifier. A quick continuity check with the cable plugged into the guitar and the amp, checking continuity from the shielding in the guitar to the amp chassis, might reveal dirty or corroded connectors or a problem with the guitar cable. The continuity reading should be 0 ohms, otherwise you'll have some hum.

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