Wiring problem..Rotary switch

[Chris Richards]

My wiring skills only really extend to copying diagrams, I just wired a guitar for a friend and it has a loud buzz unless your hand is on the strings so I guess there's an earth problem, I copied the attached diagram but was wondering if there should be an earth connection to the rotary switch? Hoping someone can give me a clue...

[David King]

Is the loud buzz the same regardless of the switch position?

[Chris Richards]

Yes it is..As far as I can tell all the switch positions work, I've tried grounding the switch "structure" but that doesn't make any difference.

[Peter Wilcox]

Try changing the guitar cable if you haven't already. If you have a multimeter, check the resistance of each of the grounds from the pickups, pots and strings all the way through your guitar cable to the amp ground to see if there is a bad solder connection or a defective cable. Does the hum change with the position of the guitar, when you lay it down and walk away, or different room, different amp? Are all the grounds connected to one point, to avoid ground loops?

Here is a link http://www.prosoundweb.com/article/elim ... c_guitars/ that might yield some useful information, such as "When the guitar player touches the strings, does the hum stop? This indicates that the player’s body is acting as one plate of a capacitor. The capacitance between the body and power wiring adds to the capacitance between the guitar and power wiring, increasing the level of the hum transmitted from the power wiring to the guitar (Incidentally, the same thing happens if you replace the player’s body with a sheet of aluminum foil).

Cure: Run a wire between a ground point on the guitar and the player’s skin. This grounds the player’s body, so that it acts as a partial shield for the guitar, rather than a capacitor. A body close to the guitar increases hum, and connecting the body to the guitar ground stops the hum. The body is not a ground for the guitar. Rather, the guitar ground is a ground for the body."

Another link to wade through:
http://forums.prosoundweb.com/index.php ... 138.0.html

Good luck.

[David King]

Best way to ground a player is to solder a wire to a gold tooth -but don't pull too hard...
Humbuckers should be totally quiet if they are wired correctly in either series or parallel configuration. Are the humbuckers of the same make? No two manufacturers use the same color code. It's also not impossible that the internal wiring or the magnet polarity got switched in the manufacturing.
Are you using shielded wires or are the guitar cavities shielded?
Regarding the house wiring, are you in a room that has multiple switch wiring runs and 3 way switches? See if the problem persists in another location.

[Chris Richards]

Thanks for the advice ...I'll get to checking the earth connections, it just bothers me a bit that there's no earth to the switch although I have looped a temporary connection to the chassis and it makes no difference..Thanks again

[Joshua Levin-Epstein]

This may seem obvious, but is the output jack wired correctly (Sleeve=ground, tip = hot)?

[Chris Richards]

Yep.... I've looked at the jack plug and that's fine....

[David King]

Well the first thing to do it these circumstances is to wire each pickup solo to the jack and see what you get. If you can isolate all the parts and track down where the noise is coming in we won't have to play the guessing game
Many pickups are wound with a slight coil offset so that they don't cancel hum completely. Supposedly this "opens up" the tone a bit and is worth the slight increase in noise that's induced.

[Chris Richards]

Hi all and thanks for your help.... I thought I'd report back having now kind of solved the problem, I couldn't definitively find the problem that was causing the excessive hum but I did read that in order to use a rotary switch for some selection combinations the pickups have to be built in a certain way, apparently if you place the pickups face to face they should attract one another then you're ok if they repel then you're going to get a hum... Like I said in my previous posts I'm no expert when it comes to wiring... So my solution was to change the wiring and go for much simpler/more standard pickup selection options which worked.

Personally I can't see why anyone would opt for a rotary switch, I would have thought that they would be pretty ungainly to use "in anger"..... But hey ho each to their own...

Thanks again for your help
Chris

[David King]

It's fairly easy to flip the magnetic polarity of an HB pickup. You have to remove the cover, there are four brass screws holding the coils to the baseplate from the underside. If you loosen these or remove two of them and warm up any potting wax around the magnet the magnet will slide out and can be reinserted after being flipped over or end-for-end.