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Topic: need help for excessive hum |
Don Barnhardt
From:
North Carolina, USA
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Posted 3 Nov 2016 3:37 pm |
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| I have been building lap steels for 3 or 4 years. It's been a learning experience. I've reached a point where they look decent and sound good but every one has a hum that I can't figure out. I'm using good components and have changed amp cords. I've resoldered all connections and have good ground connections (bridge, nut, strings, ground side of my output jacks) also use shielded wire from volume pot to output jack. I don't get any appreciable hum when I hook up my pedal steel to my amp. I expect a slight hum with single coil PU's while the hum is tolerable jamming it bothers me. I would appreciate input from other builders. It's got me stumped. |
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Clyde Mattocks
From:
Kinston, North Carolina, USA
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Posted 3 Nov 2016 4:54 pm
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Are you running a ground wire to something metal that is connected physically with the strings? You need that.
_________________
LeGrande II, Nash. 112, Fender Twin Tone Master, Session 400, Harlow Dobro, R.Q.Jones Dobro |
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Robert Allen
From:
Tennessee, USA
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Posted 4 Nov 2016 6:22 am
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| To avoid what is called a "ground loop", all grounds must come back to one common point, usually the housing of the tone or volume pot. Ground the tailpiece. Buy conductive shielding paint from Stew-Mac and paint three coats in the cavity allowing 24 hours between each coat. Apply a copper strip after the paint dries and then using a ring terminal run a wire from the copper strip to your common ground point. Every Melbert lap steel has this and I've never had a problem with hum. |
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Tom Pettingill
From:
California, USA (deceased)
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Don Barnhardt
From:
North Carolina, USA
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Posted 4 Nov 2016 7:32 pm
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| Thanks for the response. I run a ground wire from my bridges to the back of my volume control as well as the common lead of my pickup and the ground of my output jack. Also run a jumper between the the backs of my controls. Hadn't considered the shielding paint I plan to try both recommended coatings. |
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George Piburn
From:
The Land of Enchantment New Mexico
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Posted 5 Nov 2016 5:23 pm Ground lugs
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I am confident you are already there , to make sure ,
both volume and tone pots use one of the lugs for ground, make certain they are tied to the covers too.
If you are hanging your pickups from a Pick Guard type material you want to Shield that too, and have it encase the shielded pickup pocket entirely.
Add it to the grounding too.
Another Trick we use on Single Coil PuPs is to protect the coil over the waxed fabric E-Tape with several coats of the Copper Tape then another Fabric Tape to hold them and for cosmetics. This is added to the Ground Plane.
Do Not touch the Magnets though!
As Tom pointed out, shielding will help protect from EMI not so much for Inductive Hum. That topic gets more complicated.
_________________
GeorgeBoards S8 Non Pedal Steel Guitar Instruments
Maker of One of a Kind Works of Art that play music too.
Instructional DVDs
YouTube Channel |
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Jack Hanson
From:
San Luis Valley, USA
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Posted 6 Nov 2016 11:05 am
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Many thanks to Don for posting this topic, and to Clyde, Robert, Tom, and George for their expert commentary.
Is it possible to have too much grounding? How much would be overkill. If the control cavity is shielded by the Stew-Mac copper tape, will the pots all be grounded through their contact with the tape? |
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Joe Elk
From:
Ohio, USA
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Posted 6 Nov 2016 2:35 pm
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I doubt that you could have too much grounding.
I forget who advised that you need to to include some attachment to the stings. I have used that. I generally use a wire to the bridge and run it wire to one of the grounds on the pots. Worked for me.
Joe Elk |
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Don Barnhardt
From:
North Carolina, USA
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Posted 7 Nov 2016 10:35 am
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| The hum I am experiencing is fairly low freq,I'm assuming 60 cycle. I do have the end terminals soldered to the control cases. I appreciate the feed back. I would like to especially thank Tom and George for all the tips you have shared with us on this forum. Special thanks also to Bob Allen. |
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Eric Gross
From:
Perkasie PA, USA
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Posted 11 Nov 2016 4:17 am
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| I noticed when I lay my lap steel on my workbench it has a noticeable hum, looking underneath the workbench I can see the AC wiring is running directly under the lap steel. If I move it away the hum goes away. So make sure you are not close to any AC sources, a good experiment would be try playing in a different room, or somebody else's house or music store, and see if the hum goes away. Maybe the outlet is not grounded properly? |
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Peter Jacobs
From:
Northern Virginia
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Posted 11 Nov 2016 7:59 am
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I had an oddball hum issue with a single coil blade pickup -- it was well shielded with copper tape around the coil (similar to George's description). If I held the instrument on it's side (like a fretted 6-string), it was dead quiet. As soon as I laid it in my lap, I'd get a loud, low hum.
No amount of shielding or different grounding schemes fixed it, so I pulled it to save for a Strat project. It's a shame - it's a great sounding pickup, but I can't live with the hum.
_________________
Peter
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www.splinterville.com
YouTube: https://www.youtube.com/@splinterville6278/videos |
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Tom Pettingill
From:
California, USA (deceased)
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Posted 11 Nov 2016 9:56 am
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| Eric Gross wrote: |
| I noticed when I lay my lap steel on my workbench it has a noticeable hum, looking underneath the workbench I can see the AC wiring is running directly under the lap steel. ... |
Good point Eric. Close proximity to electrical mains can be very troublesome. When picking a room / place to play, its a good idea to stay away from any wall / area / room where the electrical service, meter, and breaker boxes are or comes in.
_________________
Some misc pics of my hand crafted steels
Follow me on Facebook here |
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Don Barnhardt
From:
North Carolina, USA
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Posted 11 Nov 2016 2:13 pm
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| Thanks again for the response. On the advice of bob allen I tried hooking up to a battery operated VOX amp and no hum. Took m Blues Jr out on the deck and very little hum. Leading me to believe that it's not a problem with my workmanship which was my main concern. Still have to figure out what's causing the hum. I've checked my outlets for proper ground and they seem ok . I may be picking up magnetic field from the wiring or from lights. Do these new lights (the florescent spiral kind) produce interference? |
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George Piburn
From:
The Land of Enchantment New Mexico
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Posted 11 Nov 2016 2:39 pm lights
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Screw in fluorescent do cause hum in a big way.
There is a little helper called a X-Hum or something like that , supposed to help.
The modern high shield low capacitance Cables are a help too. I upgraded to the Plant Waves and it did all sorts of good.
About the copper tape good enough question , Roberts Wireing - including the cases soldered will do better than just the copper or just the stew-mac graphite paint alone.
Computer monitors , TV Sets , Neon - transformers - microwaves - all of that stuff can induce hum even with them turned off
try unplugging all of the extra stuff you can. Lastly , in a completely quiet room hum is more apparent.
The Blues JR type amps typically have filter caps at the power in area for hum drain that go old and leak, most have those polarity switches.
Still haven't said what exact pickup you are focused on.
_________________
GeorgeBoards S8 Non Pedal Steel Guitar Instruments
Maker of One of a Kind Works of Art that play music too.
Instructional DVDs
YouTube Channel |
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Robert Allen
From:
Tennessee, USA
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Posted 11 Nov 2016 6:59 pm
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| Theoretically there is a way to completely eliminate 60 Hz hum from the output of any device if the output is fed into a differential amp chip before the signal is fed into the main amp. For example, when they do an EKG, they don't ground the patient. Therefore there is a large amount of 60Hz hum present in the leads which are fed into a differential amp to cancel the hum. With a differential amp the instrument is not grounded (called a floating ground). The hot lead connects to one input of the amp and the floating ground is connected to an input which inverts the signal and therefore the hum is canceled. The only thing coming out is the difference signal which is the pickup output without the 60 Hz hum. The output is referenced to ground. In my other life, I built these circuits for industrial test equipment but never tried it on a lap steel. Might be an interesting project. |
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George Piburn
From:
The Land of Enchantment New Mexico
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Stephen Cowell
From:
Round Rock, Texas, USA
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Don Barnhardt
From:
North Carolina, USA
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Posted 12 Nov 2016 4:25 pm
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| Thanks again. I don't have any dimmers but I do have a florescent screw-in ad my laptop nearby. I think I'll try that Hum-X plug and a pair of those planet wave cables. I use a Sho Bud pedal(all my wires are shielded). My Blues Jr. is fairly new cap should still be good. I'll keep that in mind for future reference. |
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Don Barnhardt
From:
North Carolina, USA
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Posted 12 Nov 2016 7:26 pm
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| Oh by the way, I have one George L pickup and the rest are True Tones. |
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