[xnothingpoetic]

Story:

Today I heard distortion in the left channel of my headphones, and I also heard a helicopter. I paused the music (still hearing distortion noise), and as soon as the copter got further and further away, the less distortion, until both were gone.

I'm not sure what kind of helicopter it was (never saw it), but living in the city and experiencing this has shown me that I am not immune to things like that.

So I was thinking of building a faraday cage around my amp, and probably my D/A converter as well, using cheap copper mesh from a local store. See if that helps any.

Question:

I'm not big on this stuff, but should I ground the cage or not?
Also, do you think it would help any for interference like that?

Update:
I just called my Cell and waved it around both amp and DAC, and got more interference (worse on the DAC, but there on both)

 

[grawk]

Yes, it's not a faraday cage if it's not grounded.

 

[beerguy0]

Quote:

Originally Posted by grawk /img/forum/go_quote.gif Yes, it's not a faraday cage if it's not grounded.

What grawk said. Grounding is what makes a Faraday cage work. We have screen rooms (and solid rooms) where I work that we use for sensitive RF measurements (spurs, emissions testing, etc.) They are basically giant Faraday cages, with special doors and ports that allow you to keep your measurement instruments outside the screen room.

 

[xnothingpoetic]

Thanks guys. I had to ask because I remember reading something on these forums that conflicted with what you said, but I wasn't sure.

I'm going to head out to the store soon and get the materials, and then play with my cell to see if it works.

 

[grawk]

You're gonna need to make sure your cable is shielded and that somehow your headphones are shielded too, to eliminate rf noise. maybe make copper chainmail

 

[xnothingpoetic]

Quote:

Originally Posted by grawk /img/forum/go_quote.gif You're gonna need to make sure your cable is shielded and that somehow your headphones are shielded too, to eliminate rf noise. maybe make copper chainmail

My IC's are already shielded. If I want to take it further, they make a copper techflex

How important would it be to shield the HP's? If most of the noise is from the DAC and AMP, shouldn't that be good enough, or would not shielding the HPs defeat the purpose? They are low impedance cans...

Maybe I will just isolate myself from the rest of the world. I will build a copper bubble.

 

[steaxauce]

I'm pretty certain that no helicopter can create a large enough emf to interfere with your setup down here on earth. It might've been because of vibrations caused by the helicopter, or it might've been interference from something else that just happened to occur exactly when the helicopter passed over. A faraday cage will help with RF interference (which is definitely a common issue), but it shouldn't have anything to do with any noise in the signal caused by a passing helicopter.

 

[xnothingpoetic]

Quote:

Originally Posted by steaxauce /img/forum/go_quote.gif I'm pretty certain that no helicopter can create a large enough emf to interfere with your setup down here on earth. It might've been because of vibrations caused by the helicopter, or it might've been interference from something else that just happened to occur exactly when the helicopter passed over. A faraday cage will help with RF interference (which is definitely a common issue), but it shouldn't have anything to do with any noise in the signal caused by a passing helicopter.

The way I heard the interference, made it sound like it was defiantly the helicopter. Maybe it was a police helicopter or a news one.

First I heard the copter loud and clear, and same with the noise. Then as it got further away, the noise started to stutter, then the noise went away and the copter noise wasn't heard shortly after.

That is irreverent anyway, because as I heard, I am subject to these EMI and RF signals.

 

[Budgie]

The smaller the holes in the copper used for the shield, the better.

 

[grawk]

If the headphones are electrically connected to the system, the headphones and cable are acting as a giant antenna.

 

[xnothingpoetic]

Well an update:

I feel like Patrick now

I built two cages out of copper mesh, and to top it off, I covered them in foil.

I feel like one step away from wearing a foil hat

But seriously, it works very well. I placed my cell phone directly over the transformer on the DAC, and DEAD silent. Even by the IC's I hear noting.

also hiss has gone down some as well. Before I could hear hiss around 11 o'clock, now it's like at 4 o'clock (way beyond going deaf range). But I still get a little humming from the amp around 1 o'clock- that has always been like that, but I never, ever go past 12 o'clock anyway.

Update 2: Reworked the cage to cover all holes. Hiss went down even further and for some reason I get NO tube humming. I'm not sure how it went away, but everything is dead quiet.

 

[royewest]

I know this is an old thread but I'm hoping you might still be about and remember this topic.

I just started working for a company that writes sw for cell phones, so I'm surrounded by all kinds of EMI that make my little tube amps unlistenable. And I'm in the office a lot more than in previous jobs, in a cube, so headphones are a life-saver.

I'm going to try what you tried, but I'm wondering, why the foil? Did you try it without the foil? I don't want to cook the tube amp by cutting off all air circulation.

Thanks!

 

[ericj]

you don't have to use foil, you can use a mesh - but the holes in the mesh must be smaller than the shortest wavelength you are trying to block.

I had a similar situation working at a place that had a lot of prototype electronics running completely unshielded. I was just using a glorified cmoy with an external center-tapped transformer but what ended up working was grounding the mint tin to the CT where it entered the case (din connector), isolating the input and output jacks from the enclosure, and ferrite beading all the ins and outs.

 

[les_garten]

Quote:

Originally Posted by xnothingpoetic /img/forum/go_quote.gif Story: Today I heard distortion in the left channel of my headphones, and I also heard a helicopter. I paused the music (still hearing distortion noise), and as soon as the copter got further and further away, the less distortion, until both were gone. I'm not sure what kind of helicopter it was (never saw it), but living in the city and experiencing this has shown me that I am not immune to things like that. So I was thinking of building a faraday cage around my amp, and probably my D/A converter as well, using cheap copper mesh from a local store. See if that helps any. Question: I'm not big on this stuff, but should I ground the cage or not? Also, do you think it would help any for interference like that? Update: I just called my Cell and waved it around both amp and DAC, and got more interference (worse on the DAC, but there on both)

Has it dawned on you yet, that the bigger problem here is the Black Helicopters?

.