Copper tape &/or Conductive paint - sources and suggestions

[Geek99]

2 hours ago, NancyJohnson said:

As I understand it, shielding just serves to reduce interference from both inside and outside of the cavity.  If you're in a room where you have florescent lights or (in the case I had at one particular rehearsal room) my set up picking up audio from the next room AND mini-cab radio, shielding will lessen that stuff coming out of your amp.  The OP is more about a grounding/earthing issue, which suggests something is a bit off with the bass maybe?

I suppose this is how these threads meander!

I do agree that he probably has at least one other issue. My stingray clone benefited from shielding but he likely has a grounding issue too. 

Edited March 22, 2020 by Geek99

[Woodwind]

2 hours ago, Geek99 said:

I do agree that he probably has at least one other issue 

Perhaps not bass related 😂

[rmorris]

On 22/03/2020 at 09:03, Geek99 said:

Surely the take-in of the emf causes a current in the shielding, you need to take that away. The energy doesn’t die if you leave it there, although it equally doesn’t die if you ship it to ground, but al least it’s not bothering you any more 

Basically - in a hand waving sort of way - a shield reflects most of the rfi and a small amount is absorbed depending on the Surface Transfer Impedance (STI) of the shield material, the frequency of the interference and the thickness of the shield.  A small finite amount 'gets through' the shield. Basically the better a material is as an electrical conductor the better it is at screening eg Copper is better than Aluminium.

The important thing about implementing a shield is that it is held at a fixed potential with respect to the electronics. This almost always means a good solid connection to 'ground' or 0V. This may, or may not, be connected to the actual 'Earth'.

(The 'Earth' connection is essentially for electrical safety - think about a car or aeroplane where there is no galvanic connection to earth but screening considerations still apply)

Bear in mind that different considerations apply where the interference has a large magnetic field component (as opposed to electrical field) component. In practice this means mains hum caused by transformers etc.

 

 

[Geek99]

13 minutes ago, rmorris said:

Basically - in a hand waving sort of way - a shield reflects most of the rfi and a small amount is absorbed depending on the Surface Transfer Impedance (STI) of the shield material, the frequency of the interference and the thickness of the shield.  A small finite amount 'gets through' the shield. Basically the better a material is as an electrical conductor the better it is at screening eg Copper is better than Aluminium.

The important thing about implementing a shield is that it is held at a fixed potential with respect to the electronics. This almost always means a good solid connection to 'ground' or 0V. This may, or may not, be connected to the actual 'Earth'.

(The 'Earth' connection is essentially for electrical safety - think about a car or aeroplane where there is no galvanic connection to earth but screening considerations still apply)

Bear in mind that different considerations apply where the interference has a large magnetic field component (as opposed to electrical field) component. In practice this means mains hum caused by transformers etc.

 

 

Ok that is so totally far ahead of what I was saying and any way I could have expressed it but I think my point survived your expert scrutiny; the shield cannot usefully work without a connection to “ground” on the jack socket (whether or not that actually connects to the Earth) as that’s the only way you will shed troublesome EMF. This is what I was disagreeing with in @nancyjohnson post 

[Chienmortbb]

On 21/03/2020 at 19:21, rmorris said:

All things being equal Copper is a more effective shielding material.

Generally Aluminium tape is thicker and that negates the improved conductivity. However I agree that copper is better. Neither is any used for magnetic shielding but as most of the noise we get now is RF pulses from  various appliances, that does not matter.

 

 

[rmorris]

On 28/03/2020 at 13:36, Geek99 said:

Ok that is so totally far ahead of what I was saying and any way I could have expressed it but I think my point survived your expert scrutiny; the shield cannot usefully work without a connection to “ground” on the jack socket (whether or not that actually connects to the Earth) as that’s the only way you will shed troublesome EMF. This is what I was disagreeing with in @nancyjohnson post 

yeah - I was really just expanding on the point. (You may have guessed that this sort of thing is part of my 'dayjob' so may as well share here). But, as you say,  essentially the shield/screen needs to be at a fixed potential (voltage) with respect to the circuitry. This is best achieved through a 'solid' connection to the circuit 'ground' or 0V. Cheers.

[rmorris]

On 28/03/2020 at 14:45, Chienmortbb said:

Generally Aluminium tape is thicker and that negates the improved conductivity. However I agree that copper is better. Neither is any used for magnetic shielding but as most of the noise we get now is RF pulses from  various appliances, that does not matter.

 

 

I see. I don't think I've ever used Aluminium tape, Probably due to the reasons you outline - adhesive / soldering.

But I've used 'loads' of aluminium foil in testing scenarios to good effect. On an anecdotal level from my EMC test lab mate - it's worth getting the 'Turkey Foil' mainly sold around Christmas time that is a bit thicker than normal foil. After that the law of (exponentially) diminishing returns means it's not worth going further 🙂