Proper Grounding for Pickup Cavity Shields

[persistence48]

I am researching how to properly ground copper foil when used to shield the control and pickup cavities in a future build. I will have my volume pot directly screwed into the body, which suggests that given the back of the pot will be grounded, that will inherently connect the ground to the foil without need for a separate wire connecting the two. However, I will be shielding two humbucker cavities as well, which will not have a direct connection to the shielding in the control cavity. Because of this, will wire need to be ran from the back of the volume pot to the foil in the pickup cavities to ensure a common ground?

 

[JohnnyHardtail]

However, I will be shielding two humbucker cavities as well, which will not have a direct connection to the shielding in the control cavity. Because of this, will wire need to be ran from the back of the volume pot to the foil in the pickup cavities to ensure a common ground?

Using a single grounding point such as the back of the volume pot is effective. That is normal practice of "star grounding". These connections do not carry the actual signal from the pickup because the shielded cable for the pickups provide this. In this case it is Not important how the cavity shielding gets grounded. It can be done either by connection the "star ground" point as you wrote or otherwise just connect them by soldering wires between each compartment that has copper foil shielding.

I suggest its better to AVOID the screws, pickup ring, or pickup itself coming into electrical contact with the shielding in the cavity. The Humbuckers already have their own ground wire connection to the back plate. Being grounded by the sheilding in addition to this would create a "ground loop" which is more likely to pickup noise from the environment. A lot of humbucker guitars don't use shielding in the pickup cavities anyway.

 

[persistence48]

Thank you for the info. I have previously only had guitars with shielding paint in the cavities, so I am trying to get a better understanding of the copper tape as it seems to be a grounded faraday cage, whereas the paint creates more of an ungrounded cage (unless a grounding wire is screwed into it). I have also read that ground loops are technically not possible in passive guitars, so would that not actually be an issue in this situation? In any case, it seems like given the cavity would not be fully enclosed as the pickups are exposed, it's probably not worth shielding the pickup cavities, and the wires going from the pickups to the control cavity will be shielded by default anyway.

 

[JohnnyHardtail]

Thank you for the info. I have previously only had guitars with shielding paint in the cavities, so I am trying to get a better understanding of the copper tape as it seems to be a grounded faraday cage, whereas the paint creates more of an ungrounded cage (unless a grounding wire is screwed into it). I have also read that ground loops are technically not possible in passive guitars, so would that not actually be an issue in this situation?

IMO, the ground loop is more likely to be an issue if your pickups have what is called by SD as "single conductor" wiring, where the outer cable shield functions as both signal ground AND grounding for the backplate. It could be less of an issue where 4-conductor pickup wiring is used.

There is always the possibility of a loop picking up radio interference / EMI. I used to informally test electronic devices using a mobile phone as a source of radio signal. It was more of an issue for some electronics with the old 2G cell phones from the 90s.

Have a look at the blog by Lindy Fralin.

Understanding Guitar Grounding

Guitar Grounding can be an elusive subject, but it doesn't have to be. Learn from Fralin Pickups the best practices for Guitar Grounding.

www.fralinpickups.com