I am new here, just stumbled over this discussion through a web search.
May I add a few remarks.
I have a Strat guitar equipped with single coils. All cavities and metal parts are shielded and tied to a common point. This used to be connected to signal ground with a 600V cap as described above (470 nF if I recall correctly). I bridged the cap later since it made problems I cannot remember. So it is stock so to speak as far as ground wiring goes.
I have installed a big air-coil á la Suhr which makes it vastly insensitive to external hum and the like.
This is just to describe the situation I am talking about.
This guitar is totally insensitive to proximity. It is quiet, whether I touch the strings or not.
I also own a LP look-a-like equipped with L-90 pickups (humbuckers), treated as above with the cap intact.
I noticed some funny hum problems when I turned the volume pots which I attributed to the cap.
It was clearly a ground loop problem, not mains hum. The pickups are dead quiet, which can be proven if they are switched to single coil.
For the moment, the cap is disabled and that hum is gone.
However this guitar is very
susceptible to the described phenomenon of string noise when untouched despite proper shielding, grounding etc.
If I find anything I will post it here.
One remark on the 100kOhm resistor: although 1/4 W may suffice for matters of power disappation, the resistor may not be rated for such big voltages. For this reason, I would recommend using a 2W type metal oxide or the like. A look at the specīs will make you wiser.
I will see if this "mod" does make the earlier described hum problem go away.
Also, I agree that an amplifier should be grounded properly, but this does not nedessarily mean that the signal ground
is on earth potential. In fact it may not even have any relation to earth. AFAIK there is no global rule for doing this. Up till now the best version I saw was here
, but this does not help us for given equipment.
I recently had a lunchbox amp that produced funny crackling noises dependent on the guitar when you wiped your finger over the plastic - static electricity.
It turned out the thing was not earthed at all, it was fully encapsulated, which is technically correct.
The phenomenon was cured by connecting a cable from its recording output to, say, a Fender amp input (turned off), which is grounded. This was ridiculous and the amp was returned despite any other virtues it may have had. The company was not aware of such problems, but it is a shame that they are not aware of persistent noise problems coming from antenna pick-up.
Helmut, from the Tyrol, Austria