Help! what is causing hum?

[Dale M Williams]

I need some help. I have a 2005 Essence with Europa controls. It's my only bass which makes this post a bit urgent.
 
I first noticed a hum through headphones.  With my new amp, Epifani ul-501, through 2 Epifani ul-2, 112's, the hum has become very loud.  
 
The following does not affect the hum:
 
  volume, full
  led's off
  all switches flat
  pan middle (panning front to back does not  
     affect hum)
  low pass filter.
 
Only the following will stop the hum:
 
  touching either end of instrument cable (yes, I've tried other cables)
  touching any of the four toggle switches
  (with bass on and backplate off) touching   instrument plug housing
  *Curiously, touching any painted side wall inside control cavity with bass on*
 
Any thoughts, suggestions, or solutions would be very welcomed.  Please see attached photos.  
 
Thank you very much.  
 
Dale

[Dale M Williams]

Sorry, not sure if these photos downloaded

[dfung60]

When you have a hum that goes away when you touch parts of your bass, this means that part of the shielding has lost it's connection to ground.  When you touch your cable or the switches, you're grounding your body and acting as part of the instrument shield, blocking the hum!
 
If you're lucky, the problem will be related to the contact between the back plate and the paint inside the control cavity.  The bare metal of the inside of the back plate needs to touch the painted area around the cavity.  There shouldn't be any paper, tape or corrosion on the backside of the plate.
 
The bad part is that it's really hard for the problem to be here.  If this isn't the problem, then you probably have a loose wire inside the cavity, a much harder problem to debug or something is touching ground that shouldn't be. This is the more likely problem - if you're in a really electrically noisy environment you might get some hum with the back plate off, but usually taking the back plate off won't lead to a lot of hum.
 
Check the backplate first and report back!  
 
David Fung

[Dale M Williams]

QUICK FIX?
Thanks for the info. The back plate appears to be clean and intact. I will proceed with the above suggestions soon.  
I'm looking for a quick fix for this weekend. Since the hum goes away when I touch either housing end(?) of the cable while plugged in, is there a better or preferred cable that might reduce hum? I'm using a 12ft Monster bass cable in the $40. range.  
Thanks, Dale in Michigan

[mario_farufyno]

make sure you're not close to fluorescent lamps or pc monitors

[sonicus]

Make sure that your AC house wiring is correct. In other words that the Hot ,Neutral , Ground  are not incorrect at the plug. You can purchase a little tester like this at most hardware stores.
http://cabletoolpros.com/index.php?main_page=product_info&products_id=178

 
 
      Also take your rig to another house and see if you still have the problem and like Mario noted in his post #769 stay away from EMI noise sources ( Fluorescent lamps CRT monitors , light dimmers  . transformers , etc... ... )

[mica]

Gosh, that picture is so tiny I can't really see what's going on under the hood.  
 
Since you can get the hum to go away when you touch the silver paint, it means that the connection to ground at the output jack is likely intact.  
 
Is there any chance the pickups are plugged in upside down? That would also produce the conditions you are describing.  
 
If you're picture is too big to post, email it me.

[Dale M Williams]

Thanks for all of the suggestions. I'll try all of the above soon. I have many clear photos, but I had to compress them in order to post. I'll email Mica next.
Thanks again, Dale