Hi,
I want to build a safe electric guitar, without electrocution risk (with a control cavity in the rear of the body and 3 single coils).
I have several points of vue of differents luthiers and suppliers, and I am confused about grounding or not the bridge.
Some of them told me: yes you have to ground the bridge (as we can see in the course), and others told me:
If the bridge is grounded, the strings are grounded. If you, or the instrument, catch electricity for some reason (because of a defective microphone, or a defective amplifier), then the grounded bridge gives that electricity a path... through you.....
And they recommend me to use an electromagnetic-blocking paint, for the control cavity.
Active pickups are also an alternative, but how do you do with passive single coils ?
Thanks.
@mario grounding the bridge and covering cavities with shielding copper/aluminium foil or conductive paint is done to avoid hum. It has nothing to do with safety. In theory it will indeed pass the current through you, if you are touching strings or bridge. However, the possibility of that ever happening is rather small.
The possibility of electrocution from defective amplifiers was a real thing when using older ones from 60s or 70s which had poor safety features, but with modern equipment it’s difficult to see how it would happen. Old valve amps boosted the voltage up from mains to a higher level but modern amps with solid state electronics are much safer. The internal fuse on the amp or the one on the mains plug would blow if there was any significant current getting into the ground circuit. I think 5mA is the trip limit for a 240v supply and that wouldn’t even tickle you tongue. Have your gear checked for earth leakage and you will be ok.
Blocking paint works well for Radio Frequency Interference RFI if it’s connected to the guitar ground circuit but it’s still possible to get noise into the system through an old amp that’s not shielded so you have to look at the whole system.
Not sure what you mean by active pick ups, do you mean with shielding paint or how to make passive pick ups into active.
Some people call me a tool, others are less complimentary. Tools being useful things.
Koendb 04/08/2021 1:22 pm
@Rocknroller912 active pickups have less coils, which also elimnates hum, but don't have enough current to be amplified like a passive pickup, therefor need some extra help; they have a little pre-amp stage and need a 9v battery to power that active circuit.
At least that is how I understood active pickups work 🙂
Rocknroller912 04/08/2021 3:05 pm
@koendb
Thanks I’ve got experience of building simple active amplifier circuits but I didn’t know much about active pick ups and how they are constructed. Less coils must mean a lower impedance.
I think what @mario meant about using active pickups is that you don’t need to connect the bridge to ground as they are so quiet, therefore eliminating that connection.
Using active and passive pickups in the same guitar is possible but not really ideal. When both are selected the active overpowers the passive so you lose the sound of two pickups. But selected individually it works ok.
Practice on scrap...
@rocknroller912 With active pickups I meant the system described by @koendb and @ : pickups that use a 9V battery.
EMG pickups for an example, they have their own circuit. I don't know their performance, never listened.
I think I will keep your idea @rocknroller912 and ask for some electrician to check for earth leakage....
I have also read in the book of Martin Koch, that for being on the safe side : connect the strings to ground via a high-ohm resistor and a capacitor switched in parallel.
Thank you for all your replies.