Very often we get enquiries from customers about hum issues in their guitar rig. Sometimes it's problem with their amps or pedals / pedalboards (especially with powering the pedals). However in most cases the hum comes from a guitar. Usually a dirty power in some venues, light dimmers (either stage ones or those use at home), laptops / desktop computers or their switching mode power supplies make it even worse.
Now we'll tell you how to find out if it's your guitar humming or something else in your setup. It's very simple. Connect the guitars, pedals and the amp as you normally do. Set the levels to usuall volume you play with. I'm sure you get some hum, hiss, etc. Now turn the volume control down to zero. Is the hum gone? If so then it comes from you guitar. If it's still there - it comes from the rest of your rig. If it's partially gone then part of it comes from the guitar and part of it from the rest of your guitar setup. Easy, isn't?
Obviously single coil pickups will be much more noisy than humbuckers. It's worth mentioning that P90s, Jazzmaster and similar pickups are pretty much an over-wound single coil pickups and will be also pretty noisy.
There are two quite effective ways to reduce guitar humming. Dummy coils and shielding. We'll focus on shielding as it's much cheaper and with a very little cost every a bit technical guitarst can do it himself.
It's worth mentioning about some dummy coil aftermarket systems. One very versatile and effective was invented and manufactured by Ilich Electronics. Later used in Suhr guitars. It's very easy to install as they come as a built-in in either Strat backplate or guitar scratchplate (Strat, Tele) with installation and setup manual. We've fitted it a quote few times and it really does the job.
Guitar manufacturers try to reduce it, but using a graphite spray shielding. This is only a partial help though. Mainly because the spray layer is quite thin and secondly the sprayed graphite doesn't have a zero resistance. Measuring it between various points of the sprayed cavity you get results between a few ohms and few kilo-ohms which obviously it's not a great result.
Over the years we've tried various methods, but so far the best is a copper shielding. There are various copper materials available on the market. For the easiest application we advise to go for an adhesive copper film, but as during the whole process we cut it in many small the important thing is to make sure that the adhesive layer is also conductive as otherwise you need to joint all the small copper bits with something conductive (solder a wire or so).
As you probably noticed some guitars with a scratchplate (Strat type, etc.) have a shileding at the back of it. That helps very little as the interference would still affect the pickups and the rest of guitar electronics.
Over the years we've shielded only pickups and control cavities. The result was good, but there was still room for improvement. A few years ago we've tried to shield also the pickups (the pickups shielding is hidden under the pickups covers, so it's unvisible). That gives pickups another layer of shielding from all the directions (not only from underneath) and makes guitars pretty much virtually silent.
One very important thing you have to remember while shielding a guitar is to connect all the cavities together (unless it's one big Strat-like cavity). That is required in all the guitars with body mounted pickups (no plastic pickup rings), all Les Paul and Telecaster style, etc. Usually a thin wire (we use silver one for the best result) connecting the cavities is enough.
We hope that the article helps you to understand the source of a hum in guitar rigs and ways to eliminate it.