Help! what is causing hum? Log Out | Topics | Search
Moderators | Register | Edit Profile

Alembic Club » Owning an Alembic » Troubleshooting » Archive through February 17, 2014 » Help! what is causing hum? « Previous Next »

Author Message
Username: rxbassman

Post Number: 43
Registered: 1-2004
Posted on Monday, April 16, 2012 - 7:41 pm:   Edit Post

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.

Username: rxbassman

Post Number: 44
Registered: 1-2004
Posted on Monday, April 16, 2012 - 7:57 pm:   Edit Post

Sorry, not sure if these photos downloadedphoto
Senior Member
Username: dfung60

Post Number: 548
Registered: 5-2002
Posted on Monday, April 16, 2012 - 9:21 pm:   Edit Post

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
Username: rxbassman

Post Number: 45
Registered: 1-2004
Posted on Sunday, April 29, 2012 - 5:40 pm:   Edit Post

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
Senior Member
Username: mario_farufyno

Post Number: 769
Registered: 9-2008
Posted on Monday, April 30, 2012 - 7:21 pm:   Edit Post

make sure you're not close to fluorescent lamps or pc monitors
Senior Member
Username: sonicus

Post Number: 2456
Registered: 5-2009
Posted on Monday, April 30, 2012 - 7:45 pm:   Edit Post

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. power tester

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... ... )
Username: mica

Post Number: 7716
Registered: 6-2000
Posted on Wednesday, May 02, 2012 - 3:27 pm:   Edit Post

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.
Username: rxbassman

Post Number: 46
Registered: 1-2004
Posted on Wednesday, May 02, 2012 - 5:01 pm:   Edit Post

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

Topics | Last Day | Last Week | Tree View | Search | Help/Instructions | Program Credits Administration