Copper Tape Shielding

[Bobby K]

Hello fellows

I'm considering putting some copper shielding tape inside the cavities of my P bass. I'll be doing the underside of the pickguard too. I've read a lot on this topic and I think I pretty much know what I'm doing now.

One thing that crops up regularly in the threads is that the copper tape has to be connected to [b]ground[/b] somehow. What is the best way/ways to do this?

Sorry if this sounds like a dumb question, but I just wanna do it right

[Hamster]

I would advise that you make sure there's a good join between the strips of copper tape by running solder along each join - it flows quite well.

For the cavity you can take the ground from the back of one the pots or at the jack connector - but just make one earth connection, just use a bit of insulated wire and solder onto the copper tape. For the pickguard, if you are removing all the hardware, then you'll get a good connection from the body of the pots. If you're applying the tape around the hardware then just use another bit of wire attached to the back of one of the pots.

[Bobby K]

[quote name='Hamster' post='955020' date='Sep 13 2010, 04:47 PM']You can take the ground from the back of one the pots or at the jack connector - but just make one earth connection, just use a bit of wire and solder onto the copper tape.[/quote]

So just connect a bit of wire to the existing solder blob on top of one of the pots then? I assume you mean not to connect to [b]both[/b] back of pot and the jack connector..? (just do one or the other) Just wondering what sort of wire to use...

Also, should the copper under the pickguard connect to the copper in the body cavities?

(actually, just read your post again and I think I've got it)


Cheers for your help by the way

Edited September 13, 2010 by Bobby K

[Ou7shined]

Basically you have to make sure that every bit of copper is earthed. You do this by connecting it to anything else that is metal. (which in theory is already earthed). It would be impractical to solder to your p/g (plus it would melt) so you can leave an overhang out the top of the cavity and make sure that the copper on the underside of you p/g touches it. Simples.

[Bobby K]

[quote name='Ou7shined' post='955061' date='Sep 13 2010, 05:19 PM']so you can leave an overhang out the top of the cavity and make sure that the copper on the underside of you p/g touches it. Simples.[/quote]

Good man, that's exactly what I was thinking of doing; just needed somebody to confirm it was ok to do

[Hamster]

[quote name='Bobby K' post='955035' date='Sep 13 2010, 05:00 PM']So just connect a bit of wire to the existing solder blob on top of one of the pots then? I assume you mean not to connect to [b]both[/b] back of pot and the jack connector..? (just do one or the other) Just wondering what sort of wire to use...

Also, should the copper under the pickguard connect to the copper in the body cavities?

(actually, just read your post again and I think I've got it)


Cheers for your help by the way [/quote]

Just hook up the copper tape to ONE earth point. It shouldn't make a difference but the law of sod is living and active and if you do multiple hook-ups you might get a buzzy earth loop type thingy!

[Count Bassy]

In industrial applications the current recomended practice is to earth everything* to the 'earth plane' as many places as possible.
Reckoned to be far more effective for high frequency noise that you get these days (from dimmers, Telly's, PCs, switch mode power supplies etc).

In practical terms this means line your cavities with copper foil, and if possible line the drilled holes between cavities (its tricky). You could pass a bit of braided cable screen through the holes and expand it to fit, and then solder it to the copper screen at both ends if you wanted.

Then bring your incoming earth on your jack socket to the copper screen, and take any screened metal parts (eg back of pots) to the copper screen as well, with short bits of wire.

As people have said above, you then need to keep your signal common separate from the screen earth, except where you connect onto the jack socket.

Ideally you'd keep the screen earth and signal 'earth' separate all the way back to (and inside) the amp, but the ubiquitous use of coax cable for instruments generally prevents this.


*Obviously when I say 'everything' I mean everything that isn't part of the signal path or 'live'.

Edited September 14, 2010 by Count Bassy

[Bobby K]

[quote name='Count Bassy' post='955635' date='Sep 14 2010, 01:27 AM']and if possible line the drilled holes between cavities[/quote]


What about the drilled hole for the ground wire that attaches to the underside of the bridge....? Do i simply just carefully apply the foil around this hole?

[Ou7shined]

[quote name='Bobby K' post='956161' date='Sep 14 2010, 04:11 PM']What about the drilled hole for the ground wire that attaches to the underside of the bridge....? Do i simply just carefully apply the foil around this hole?[/quote]
There is no need as it already is a ground wire and carries no actual signal.

[Count Bassy]

[quote name='Ou7shined' post='956203' date='Sep 14 2010, 04:39 PM']There is no need as it already is a ground wire and carries no actual signal. [/quote]

Not totally true as the wire can act as an ariel and conduct noise into the screened cavity! But in practical terms your probably right, after all this wire goes to the bridge and hence to the strings, which act like ariels anyway and I can't think how we'd screen those!

However, solder this wire to the copper screening close to where it enters the control cavity, dont take it to the jack socket earth, or the back of a pot etc, as any of this wire inside the cavity has the potential to re-radiate what it has picked up from the strings, which can then get into the signal path.

[Ou7shined]

[quote name='Count Bassy' post='956244' date='Sep 14 2010, 05:12 PM']Not totally true as the wire can act as an ariel and conduct noise into the screened cavity! [b]But in practical terms your probably right[/b], after all this wire goes to the bridge and hence to the strings, which act like ariels anyway and I can't think how we'd screen those!

However, solder this wire to the copper screening close to where it enters the control cavity, dont take it to the jack socket earth, or the back of a pot etc, as any of this wire inside the cavity has the potential to re-radiate what it has picked up from the strings, which can then get into the signal path.[/quote]
I know. You have to draw the line somewhere.

[flyfisher]

[quote name='Ou7shined' post='955061' date='Sep 13 2010, 05:19 PM']Basically you have to make sure that every bit of copper is earthed. You do this by connecting it to anything else that is metal. (which in theory is already earthed). It would be impractical to solder to your p/g (plus it would melt) so you can leave an overhang out the top of the cavity and make sure that the copper on the underside of you p/g touches it. Simples.[/quote]
That will certainly work for a while but copper tarnishes very readily in the presence of air (copper + oxygen = copper oxide), which will affect conductivity between the cavilty and p/g foils. If the two foils are pressed very hard together then tarnishing may be quite slow but, even so, a length of wire soldered between the foils but long enough to allow the p/g to be removed might provide a more robust electrical connection.

[Bobby K]

[quote name='Count Bassy' post='955635' date='Sep 14 2010, 01:27 AM']You could pass a bit of braided cable screen through the holes and expand it to fit, and then solder it to the copper screen at both ends if you wanted.[/quote]

Is this the same as the outer mesh stuff you get on coaxial cable? When you say [i]expand it to fit[/i] how do I do that?

Could I not just link the two cavities through the hole using a normal bit of insulated wire, soldered to the copper screen on both sides?

Sorry for all the questions, we're nearly there now.... :blush:

[Count Bassy]

[quote name='Bobby K' post='956593' date='Sep 14 2010, 09:43 PM']Is this the same as the outer mesh stuff you get on coaxial cable? When you say [i]expand it to fit[/i] how do I do that?

Could I not just link the two cavities through the hole using a normal bit of insulated wire, soldered to the copper screen on both sides?

Sorry for all the questions, we're nearly there now.... :blush:[/quote]



Well you could just link the two with a bit of wire, especially if the wires from pickup are themselves screened, which they are on a lot of modern style pickups, However the 'hole' in the screening where the wire goes out is a hole in the screening where noise can get in.

If the cables are not screened than you'd still be better off lining the hole/ screening the cables in some way. You might well get away without doing it, but if there's still some noise left after all the work you'll be left wondering if that's where it's coming from!.
(Rather like soldering - its easier to get the technique right and make sure that each connection is good as you make rather than throw it together and then have to go over it all again trying to find the one dodgy joint that's causing a problem.)


Re the braiding - yes use some braiding out of a good cable ('Woven' rather than wrapped around) - something out of a good microphone cabel etc would be good. After removing the braiding you'll find that it will narrow down as you stretch it, so you can poke it through the hole (depends how big the hole is), and then compress it end to end again to make it expand width ways again, against the sides of the hole. Then splay out the ends and solder to the copper foil. It is fiddly and a lot depends on the length and diameter of th hole.
I've also considered using thin walled copper tube (like you get from modelling shops) to pass down the holes, but never actually don this.


Please note, however, that I'm pretty pedantic about some of this stuff. You might get away with, or get an acceptable result without going to these measures! Two screened cavities linked by wire will be far better than no screening at all - its the old diminishing returns/Parento thing, i.e. 80% of the improvement will be achieved by 20% of the effort. However my attitude is that if you've got all the electrics out anyway you might as well do the best job you can while you're in there.


Good luck with it.

Clive

[johnnylager]

I used copper tape with a conductive adhesive, overlapped everything & it seems fine. Found it on the 'Bay. I connected the cavities with tape over the top. It's my beater though, so I wasn't too worried.

[Bobby K]

[quote name='Count Bassy' post='957222' date='Sep 15 2010, 02:24 PM']Re the braiding - yes use some braiding out of a good cable ('Woven' rather than wrapped around) - something out of a good microphone cabel etc would be good. After removing the braiding you'll find that it will narrow down as you stretch it, so you can poke it through the hole (depends how big the hole is), and then compress it end to end again to make it expand width ways again, against the sides of the hole. Then splay out the ends and solder to the copper foil. It is fiddly and a lot depends on the length and diameter of th hole.
I've also considered using thin walled copper tube (like you get from modelling shops) to pass down the holes, but never actually don this.[/quote]

Cheers Clive, your advice is much appreciated!

Right, I'm pretty sure the pickup wires aren't screened. They're very thin and after all this is a re-issue of a 60's Precision, which I'm guessing wouldn't have screened wires??

So, I pretty much need to create a copper [i]tunnel[/i] from cavity to cavity I suppose. I'm not sure if I've got any cables handy that I can butcher to get the brading, but i've been considering some other ideas.

I've had the crazy notion to cover a small plastic tube in the copper tape and cut it so it's just the right length for the hole and pass the wires through. I've also considered just wrapping the copper tape around the three wires and passing them through the hole, tacking more tape at both ends (in both cavities) and soldering to the copper cavity floor. What do you think of these ideas? Furthermore, is it feasible to join the cavities with tape over the top, as suggested by johnnylager?

I've fully lined each cavity with the copper now; just need to drop some solder on the joins between the tape, then I'll be good to go with tackling the [i]copper tunnel[/i] to link the cavities. Any further guidance you can give on the above suggestions would be most appreciated

[Bobby K]

I finished the shielding job. Managed to sort out some braided wire to go through the hole. Soldered it all neatly to the copper. Passed the pickup wires through, resoldered to the pots etc and put the bass back together. Seems to be fine.

Thanks to all who gave their advice

Edited September 16, 2010 by Bobby K

[Ou7shined]

Sounds like a dodgy connection, you've got a +ve going to earth somewhere. Trace the route from your hot line from your pup all the way up to and including the jack socket. Luckily the wiring on a P is pretty simple.

[Bobby K]

[quote name='Ou7shined' post='958326' date='Sep 16 2010, 02:05 PM']Sounds like a dodgy connection, you've got a +ve going to earth somewhere. Trace the route from your hot line from your pup all the way up to and including the jack socket. Luckily the wiring on a P is pretty simple.[/quote]

Cheers mate, but it was a false alarm

I was testing the bass through a guitar amp which unknown to me was cranked up to max volume!!

All is normal now the amp has been adjusted, sorry for the panic

[Ou7shined]

Haha classic.

[Bobby K]

[quote name='Ou7shined' post='958343' date='Sep 16 2010, 02:16 PM']Haha classic. [/quote]

After playing this bass for a few days, I'm pretty certain that the shielding job has muddied the sound a little. There is a definite loss of [i]crispness[/i] in the sound. Is this possible, or is it more likely that I've damaged something?

Very frustrating. I'm now getting the words [i]"if it ain't broke don't fix it!"[/i] going round my head. This bass was never very noisy to begin with; just at certain gigs with dodgy lights etc, there would be noise. So just thought shielding it wouldn't do any harm. Not so sure I should've bothered now

[Ou7shined]

If you are experiencing an altered sound it may be that you have a wire or something (perhaps a pickup terminal) inadvertently shorting back to earth somewhere.
Your capacitor is in charge of tone. Does everything capacitor related look ok?

[essexbasscat]

try GuitarNuts.com lots of info about sheilding (but applied to strats-theory is the same)

graphite paint can also be used for cavity sheilding

T

[LawrenceH]

I have wondered this same thing. A quick google brings up this from Audere, see about a third of the way down:
[url="http://www.audereaudio.com/FAQ_PUNoise.htm"]http://www.audereaudio.com/FAQ_PUNoise.htm[/url]

Although they're talking about their pre-amp, in HiZ mode as far as I understand it's mimicking the loading of passive pups straight into an amp, so the same would apply. They refer to compensating, I don't know how they'd achieve this though - any ideas anyone?

[Bobby K]

[quote name='Ou7shined' post='965301' date='Sep 23 2010, 09:40 AM']If you are experiencing an altered sound it may be that you have a wire or something (perhaps a pickup terminal) inadvertently shorting back to earth somewhere.
Your capacitor is in charge of tone. Does everything capacitor related look ok?[/quote]

Well, I was convinced that I'd knackered my tone pot with too much solder iron heat after first doing the job. This was after trying to unsolder the blob on top of it, having the iron on the pot for ages before realising it wasn't hot enough (but still heating up the pot!)

The tone pot was having very little effect on the sound and it was pretty woolly. Turning the tone from 0 up to 10, there was little change in tone until about 8, when the sound would brighten a little, then die off again. So, thinking I knew best, I got some CTS solid shaft pots and an orange drop cap and put those in. By the way, the old cap, a green one, looked ok (even though it was wired different to the fender diagrams) - My old pots were 250 k by the way.

Now the CTS pots and orange drop are in, things have improved a little; the tone now goes from wooly at 0 to a noticeable increase in tone at 10, but definitely not as bright as before (pre shielding job attempt) - Does it matter which way around the orange drop legs get soldered in? I did left leg (as you look at the writing on cap) to top of tone pot and right leg to middle pot lug.

A little background info as to exactly what I did in the shielding job. All cavities copper lined and tested for continuity, Pickguard underside copper foiled too and in contact with copper lipping over edge of body cavities. tunnel between cavities also copper shielded using copper tube soldered at both ends. Bridge ground wire was soldered to copper wall in cavity, right by the hole it comes out of. One thing to mention now is that my pickup has a brass plate underneath, with an earth wire coming from the bottom of it. I soldered this to the volume pot, as it was before shielding.

One thing I haven't done though is solder a wire from the copper to a particular earth point, such as the jack ground lug. I wasn't sure if this was essential. Maybe this is my problem...?

By the way, I'm not getting any noise problems, just the tone isn't what it was.