Shielding an Electric Guitar

Take the cavity covers off and we see what you might think is shielding paint in the control cavity but it isn’t. The black paint you see has no electrical conductivity what so ever. It’s just black paint. I suppose this would be a pretty easy mistake to make during the manufacturing process and is probably one of the reasons this guitar buzzes so badly.

Source : rustyohus @ The Guitar Matrix - http://guitarmatrix.proboards.com



The shielding paint I am using is from Stewmac.com. This stuff does a very good job and it gets into those hard to reach places. Just remember to keep it thoroughly mixed as you go. You could also use household aluminum foil but this is much easier to work with in the cavities. Use the foil or metal tape for the cavity covers.



An important note about conductive shielding paints. This stuff is expensive and does not last very long in storage so only purchase it in sufficient quantity to do the job you have to do now. I buy it in the ½ pint can which is actually enough to do three or four guitars. After use I wrap it tightly in plastic wrap then store it in an old plastic peanut butter jar and fill the void with sand. Sounds stupid I know but the plastic wrap helps prevent some evaporation. The peanut butter jar prevents some more evaporation and the sand displaces the air in the peanut butter jar as yet another defense against evaporation. Opening up the can only to find a carbon black rock is a real bummer when you are ready to get started. This allows me to store it for longer periods.

Here we are four days later. You need to wait 24 hours between coats and it took four coats to achieve the conductivity (below 100 Ohm resistance) needed to make a good shield.

The pickup cavities.



The control and switch cavities.

And don’t forget the output jack area.



Next we need to add grounding wires to the pickup cavities because they will have no electrical connection to ground otherwise. These wires will be terminated at the back of the pots when I put the electronics back into the guitar. The switch cavity will make its electrical connection to ground through the frame or body of the switch. The control cavity will be connected to ground through the pots.



Notice I also terminated the bridge ground to the now shielded control cavity.



If the guitar had an open frame output jack it would be wise to replace it with an enclosed output jack. This makes it easier to prevent accidentally grounding the guitar out. I have included a pic showing an open-frame output jack on the left, a plastic enclosed jack in the middle and a threaded enclosed jack on the right. For this AR250 guitar I used a SwitchCraft plastic enclosed output jack and wrapped it with heat-shrink to prevent the contacts from making contact with the grounded shield. You could also use very wide electrical tape.



I was able to get the toggle switch and volume pots to work like new just by cleaning them properly. I could not get the tone pots, especially the bridge tone pot, to work like new and they had to be replaced. The bridge pickup worked fine after cleaning and/or replacing the support components. On a side note: Since the tone cap is soldered so closely to the tone pot, it is wise to consider that cap as a dead component as well and replace both the pot and the cap.
Even after all these years and so many guitars that have found there way to my work bench, I am still amazed by how much of a difference proper shielding can make in how good a guitar sounds. Even with the stock electronic components.
For caps I like to use audiophile grade capacitors for the tone controls (The kind that are generally used in the better speaker cross-over circuits) and silver mica capacitors for treble bleeds if the guitar has or needs a treble bleed.


Both Hovland and Kimber Kap make an excellent .022uf audiophile grade cap for tone controls. The Hovland is very expensive so I don’t use those as often. If the guitar has only one tone control, I will use a Hovland. If the guitar is a full or semi-hollow body, I will use Hovland caps because those guitars are difficult to wire. It just makes sense to me to use the absolute best parts I can afford on a guitar that is extra difficult to wire. For everything else I’ll use a Kimber kap .022uf cap. Sometimes I’ll use different values such as .033uf or .044uf depending on the type of guitar and the sound I’m going for.


For pots, I use either Alpha or CTS. Most of the OEM pots I’ve seen in Ibanez guitars are Alpha pots and they are actually very good pots. As long as a pot operates quietly and test at above the Ohm rating stamped on the pot, I keep them in there. I only replace them if they are noisy and I can’t clean them enough to make them operate quietly, if they test at below the stamped Ohm rating or if they just plain don’t work.



For wire I try to use the original wire if it is already 22 gauge shielded wire and is in good condition. If the internal wire is smaller than 22 awg or in poor condition I’ll replace it with the biggest shielded wire that will fit up to 22 awg. There really is no point in using wire bigger than 22 gauge shielded wire. I’ve worked on some guitars that did not have enough room to squeeze 22 gauge shielded wire in there.

Source : rustyohus @ The Guitar Matrix - http://guitarmatrix.proboards.com