Q: “How do I stop my Gretsch from feeding back?”
A: If it has real f-holes or an access cover in the back the tried-and-true method is stuffing the hollowbody with some kind of padding. The padding is easy enough to remove and usually works. If it’s a sealed body, such as the mid-’60s Gretsch Tennessean, the procedure is a little more difficult:
Try potting the pickups. The term “potting” refers to the sealing of the coils in a solid material. Potting stabilizes the components of the pickup so that they cannot move relative to each other. This eliminates vibration-induced signals that make a pickup act like a microphone. Potting can also protect the inner coil from corrosion.
The technique is not just potting, but also “coil immersion.” Coil immersion is allowing a solid (wax) to be absorbed into the coil. Wax is used because it works well, is inexpensive, and it makes it possible to work on the pickup later. A correctly potted pickup coil will have the wax absorbed throughout the coil as well as the surrounding parts such as magnets, pole-pieces, and metal covers. This eliminates movement of parts inside the pickup. If you’ve never done this before, then it is highly recommended to have a qualified tech do it, as it is possible to ruin the pickups. For those who are more adventurous, we will discuss the necessary tools and procedures for potting. First timers should try it on a cheap guitar that they don’t care about before experimenting on a classic Gretsch.
Another less dangerous way to go is to place thin foam padding underneath the pickups (where they meet the body). While the pickups are removed, you may be able to also put some foam or padding in the body through the pickup holes, but be careful and remember you may want to remove it someday.
Another more permanent solution:
Try installing a sound post that connects the top and back. Usually when the body feeds back, it’s because the top and back are vibrating at different frequencies. Take a piece of maple (or some other type of hardwood) and cut a piece that’s small enough to fit through the bridge pickup hole. Using a tape measure, measure the distance from front to back inside the guitar and cut the wood to fit that. Put the block inside the guitar and wedge it so that it fits as close to under the bridge as possible. Since the bridge is the main transference point of the vibrations from the strings, this will transfer more energy at this point. With the wood block in place, this should severely cut down on body feedback. If this works then remove the block, put a small bit of wood glue on each end and re-install. This is an old violin trick; it helps the top and back to vibrate together instead of separately and gets more string/vibration energy from the instrument.