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Aluminium Foil Shielding Revisited (problem solved)

Discussion in 'Pickups & Electronics [BG]' started by PilbaraBass, Aug 27, 2005.

  1. After you thought we'd exhausted this subject and then the original thread was hijacked with folks talking about foil on TV antennas (not very pertinent to bass guitars, obviously)...I have some new news to report.

    I have found a way to make Aluminium foil work well as a shield material. I simply bought some double-sided cloth carpet tape (the stuff used to hold down the edges of carpeting). I then laid the foil flat (shiny side down) on a table...I unrolled a length of the tape and pressed it into the foil firmly...and then I simply trimmed the excess foil.

    now with the foil firmly bonded to the cloth tape...I cut smaller pieces as needed from the larger piece. Then I removed the backing and stuck it into the control cavity.

    With the cloth mesh firmly stuck to the foil, the foil is flexible, not subject to tearing and sticks great. It's not solderable like copper foil, but it covers great and it works like a champ.

    I covered all the cavity of my wishbass this way and testing with an ohm-meter showed that I did not have to do anything to as far as electrically joining the edges...(good continuity throughout)...

    Now I can play my bass without any noise in my practice shed (which has lights on a dimmer circuit)...before this I had to play in the dark, because the buzz was so annoying...

    now....dead quiet...

    oh yeah...I got the tape at Big-W (like K-mart here in Oz) for <$7 AU for 5m X 50mm (2") roll.

    It looks good, too. I'm so satisfied, that I've another bass that is going to get the same treatment this week.
  2. Rav


    Dec 29, 2004
    Aurora, IL

    Noise from a dimmer switch is a grounding problem and not a shielding problem.

    Dimmer swithces do not generate excessive external RF singnals.

    You not understanding the difference between a ground and a shield is the reason you think we were off topic.

  3. The reason you were off topic is because you WERE off topic...

    now explain to me why, my bass is quiet now...when the only mod I did was shield it...

    OK...forget the theory mate...it is quiet now...and the Al foil is a good shield and that is all that matters...

    end result = noiseless bass = GOOD THING
  4. Rav


    Dec 29, 2004
    Aurora, IL

    It is not a good sheild, it is conductive and thusly a good ground and you had a ground problem.

  5. Lyle Caldwell

    Lyle Caldwell

    Sep 7, 2004
    Hold on there, Rav- you're busting his balls just for the sake of busting balls.

    All that any shielding job does, be it copper foil, aluminum foil, or conductive paint, is provide a grounded enclosure for the signal. This does shield against common RFI and other sources of noise. It can also keep out the "junk" that dimmers can put on an electric supply ground. About the only thing it won't do is reduce magnetic fields, which isn't a common problem with basses.

    So there's no need to quibble over the difference between a shield and an improved ground. In practice, in this application, they are often interchangeable terms.

    I will say that the casual addition of cavity shielding to an existing circuit provides less true shielding even if the ground is cleaned up. It takes star grounding with shielding with a separation between the shield ground and signal ground (except at one specific point) to offer the best possible shield.

    BUT the difference between the two approaches is not always apparent in the average playing environment.

    I still wouldn't recommend aluminum foil as it cannot be soldered to and tears easily, but it's good to know Pilbara found a way to make it work for him.
  6. Tim__x


    Aug 13, 2002
    Alberta, Canada
    Futhermore, a dimmer switch can create significant EMI. EMI is created by di/dt, a current that changes versus time; in laymans terms a dimmer switch works by chopping up the power from the mains, in doing so it creates huge changes in current very quickly, think around 1.5 amps switched in under a millisecond for a 100 watt bulb set at half brightness (the change occurs at the peak of the waveform and peak values are higher because the bulb is slightly cooler), that's a significant di/dt.

    Back on topic, I'm glad you could make it work Pilbara.
    How did you end up grounding it?
  7. Thanks, Lyle...

    Look Rav, Faraday PROVED that charges stay on the OUTSIDE of a conductor...hence it is a Faraday shield, for ELF (extra low frequence electromagnetic radiation)...so quit busting my chops, OK?

    And lyle, with the cloth backing of the carpet tape, the aluminium foil becomes quite tough, and workable...with this stuff bonded to it, it's like night and day.


    No you can't solder it...but I didn't have to solder my application anyway (the ring of the jack provides more than enough contact. But as a safeguard, I soldered a wire to the pot case and wedged it between the aluminium cover plate and the edge of the cavity...plus there is a slight "lip" of aluminium around the cavity for this purpose as well...
  8. Le Basseur

    Le Basseur

    Mar 26, 2002
    Nice thread guys,with busted chops,etc. :smug: but I'd like to insert a small problem here:what about the aluminium surface's oxidation?
    As you know,aluminium oxidates pretty quickly and,AFAIK,the aluminium oxide is non-conductive (as opposed to,say,silver oxidation).
    What happens after a given period of time (days,months) with the contact surface between the aluminium foil and the electrical ground?The aluminium oxide's developement in the contact area(s) means that we'll have to mechanically re-tighten these spots,or clean the foil,or what?
  9. Tim__x


    Aug 13, 2002
    Alberta, Canada
    I don't imagine it'll cause any problems, the contact point should be protected from the air by the mere fact that it is the contact point. If it does cause problems the tiniest of scratches will break through the AlO2 and allow a new connection.

    For anyone else doing this, I still think copper is a somewhat better choice.
  10. I don't believe oxidation to be much of an issue, either...as I have two very good contact points from the ground to the aluminium.

    I still think copper shielding is a better choice, too...but, my DIY heart was screaming for another chance at using aluminium, and I am more than happy with the results...
  11. Would the metal tape used in Heating/Air Conditioning work as a shield? It appears to me to be made out of aluminum. I'm talking about the real metal type not the gray duct tape we all love so well. That would stick nicely to bottom and walls of the electronics area. Anyone tried that?
  12. Dan -

    I've never used this but I have heard that it works quite well. It's on my list of things to try.
  13. If either of you get around to trying that, post it up on here or PM me with the results. I'm interested in it myself, and if it goes well with you I'll give it a shot...
  14. with aluminium foil and the cloth double-sided carpet tape, the end result is very close to that of the metal duct tape.

    so far, i've done two basses, and one homemade effects box (abs plastic) with the stuff and it's holding up great. and it sticks like anything!
  15. i have used the aluminium air con duct seal tape and it works ok as the foil is pretty tough (although it does tear easier than copper) and with it being slightly less rigid than copper it moulds well to the cavities. the only thing i forgot was to do an independant ground so i was a little confused when i plugged in and got the ground hum. (im sorting out star grounding at the moment)
  16. Thunder Lizard

    Thunder Lizard

    Dec 7, 2005
    Lethbridge, AB
    Canadian Distributor, Basson Sound Equipment
    I'd think that the metal duct tape might be better, as long as the glue is conductive.
    I'd lean towards Pil having a shielding vs. grounding problem for only one reason.....with the addition of a cloth tape on the back, and done the way he did, I am under the impression that there would be non-conductive cloth between layers on any overlap...therefore, an imperfect grounding environment, as it's not electrically conductive throughout......but since the foil overlaps, it should provide better (not optimum, but better) shielding against RFI than nothing at all.
    However, I agree that shielding and grounding usually amount to the same, or at least strikingly similar, thing.
    Pilbara, I'm curious.... do you have an electrical test meter, aka "ohm-meter"? I'm wondering if you can test between any 2 points in the foil and achieve 0 ohms, or really close to it?
    Just for my own curiosity.
    I'm glad it worked for you, though! Cheers!
  17. hehehehe i feel so stupid i missed the ground wire from the active board when i re wired its sorted now dead silent with only single coil noise.

    i'd love to take a meter to my bass but i aint really electrical so i aint got one.