[Cyntax]

Hello,

I'm currently in the process of building a PPA and I still haven't decided on an enclosure. I saw some pictures of an amp built into a wooden box and was thinking of doing something like that.

Are there any considerations with going wood over a metal case? I read something in a thread about a metal case insulating the amp from outside electrical fields or something. I'm skeptical as if this is actually true, but I will be using the amp right beside a computer/monitor so I thought i'd post and see if anyone has any input on that.

Any thoughts?

Thanks!

 

[morsel]

It is true that a metal case shields the circuit and a wooden box does not, unless you line it with metal foil. I would not build it unshielded. You could try aluminum conductive paint, as was suggested recently. Not sure how well it will work, though. Once your amp is done you will be in a better position to decide how important shielding is to you.

 

[jasonhanjk]

Or you could use nickel compound screening spray. It acts as an Fraday shield.

 

[Gariver]

I have some amps that work very, very well without any shielding at all. Some of these amps are completely open in Sijosae's style, others are plastic. I guess it all depends on your surroundings.

In another thread, Voodoo says his naked, uncovered PPA works very well under an eight foot flourescent light system. Dead quiet, he says. Once again, it all depends on where you are.

 

[Voodoochile]

That is true, Gariver. I must say I was surprised, because a META or CMOY in the same place on the workbench does pick up a bit of noise. All that said, I still do prefer a full metal jacket

.

I also like wooden cases, though. If I was going for a wooden case, I would line it with copper or aluminum flashing. You can buy 'step-flashing' at a local hardware store or home center. It comes in 4" x 6" rectangles, and most places sell it per each. So you do not have to buy a huge roll, or a massive sheet of metal. The little cards are easy to handle, and in the case of the aluminum, you can score it with a utility knife, bend it, and snap it off. It works very well.

 

[fewtch]

How about something like Mu-metal?

 

[JohnFerrier]

Quote:

Originally posted by fewtch How about something like Mu-metal?

http://www.crutchfield.com/S-4Mu2vsY...uded&i=127COF2


JF

 

[fewtch]

Quote:

Originally posted by JohnFerrier http://www.crutchfield.com/S-4Mu2vsY...uded&i=127COF2 JF

Oooh... boy is that stuff pricey in small quantities...

.

Wonder what would happen tho if I got some, lacquered it to make it nonconductive (if necessary) and wrapped it around my primary source (PC sound card), leaving enough room for heat to escape? Lots of audio-related ideas come to mind with this stuff...

 

[JohnFerrier]

Mu metal is for low frequency stuff/magnetics. The place I would use it is between the transformer and sensitive circuitry (amplifier). Steel, though not as effective--though better than copper and aluminum, is a cheaper alternative. Just moving things away from each other works too.

Look at figure 16 here:
http://www.analog.com/UploadedFiles/...6254AN-347.pdf

I've wondered how easy mu metal is to cut, drill holes in, and possibly bend. I noticed in the link you provided that it indicates that mu metal is worked like stainless steel. I'd like to know if that means that it is hard for a DIY'er to use.


JF

 

[Budgie]

Thanks for pointing out that article, John. Great information.

 

[A3rd.Zero]

you may want to be aware that if you build a headphone amp in a wooden enclosure, you must make alowences for the thickness of the material. Most jacks, switches, and pots, dont have the length to make it through the ammount of wood you would need for stability. That said, if you chose your parts carefully it can certainly be done and wood audio devices are really great looking.

 

[ofb]

Quote:

Originally posted by JohnFerrier I've wondered how easy mu metal is to cut, drill holes in, and possibly bend. I noticed in the link you provided that it indicates that mu metal is worked like stainless steel. I'd like to know if that means that it is hard for a DIY'er to use.

if it's like stainless, then it's tough to cut and tough to bend.

 

[fewtch]

I'd guess it depends on how thick the mu-metal is. If it's in thin sheets (like aluminum foil) then it should have a different consistency than aluminum foil but still be easy to work with, perhaps even without tools.

I've heard that Mu-metal is for electromagnetic stuff (not purely magnetic) which might include some of the higher frequencies depending on composition of the mu-metal. I could be wrong though. At the very least it should shield RFI as well as any other kind of metal would, with the added benefit of shielding magnetic type interference particularly well (that would include fans inside a computer case, which might make it ideal for wrapping around a sound card to help reduce clock jitter).

 

[Kadail]

Or you can just get an aluminum case and anodize it some cool colors, like I did with my soon to be PPA case.

This is the Hammond 1455N enclosure. I also anodized two aluminum knobs to go with it not pictured here.

 

[morsel]

Sweet case, Kadail!