With regard to a chip amp and torroids,
and more generally to other components like perhaps a DAC powered by a torroid,
What are the cons involved in putting the unit in an enclosure that is not completely metal? For example say a metal enclosure with a clear top (to show the electronics), or maybe a completely plastic enclosure? Or wood? Etc.?
I ask this because many years ago the first project I did was a headphone amp and I "debugged" it for about 3 weeks on the benchtop because it had a slight buzzing sound. Then I got the bright idea to test it inside an enclosure and the buzzing went away.
and more generally to other components like perhaps a DAC powered by a torroid,
What are the cons involved in putting the unit in an enclosure that is not completely metal? For example say a metal enclosure with a clear top (to show the electronics), or maybe a completely plastic enclosure? Or wood? Etc.?
I ask this because many years ago the first project I did was a headphone amp and I "debugged" it for about 3 weeks on the benchtop because it had a slight buzzing sound. Then I got the bright idea to test it inside an enclosure and the buzzing went away.
The cons are more sensitivity to external noise pickup. The *grounded* metal enclosure acts like the shield to ground all the noise before it reaches the amp.
However, you don't HAVE to use metal, but you can if you like. You can also use lots of other materials! If the amp is built well, it should not pick up a lot of noise anyway, metal case or not.
I built a 350W DIY subwoofer amp with a Wooden Enclosure.
I used thin wood for the frame, and gray-blue paneling for the sides, bottom and top, and an extra piece inside on the bottom to mount the PCB, transformer, and other components, which is removable with a few screws if it ever needs repair. It even has six fans, and I get no problems with noise or hum.
I've even seen plexiglass enclosures! You could even look at a few wild computer cases to get a few ideas, or even use a computer case like Forum Member MJL21193 did for his amp. http://www.newegg.com/Store/Category.aspx?Category=9&name=Computer-Cases
However, you don't HAVE to use metal, but you can if you like. You can also use lots of other materials! If the amp is built well, it should not pick up a lot of noise anyway, metal case or not.
I built a 350W DIY subwoofer amp with a Wooden Enclosure.
I used thin wood for the frame, and gray-blue paneling for the sides, bottom and top, and an extra piece inside on the bottom to mount the PCB, transformer, and other components, which is removable with a few screws if it ever needs repair. It even has six fans, and I get no problems with noise or hum.
I've even seen plexiglass enclosures! You could even look at a few wild computer cases to get a few ideas, or even use a computer case like Forum Member MJL21193 did for his amp. http://www.newegg.com/Store/Category.aspx?Category=9&name=Computer-Cases
I still can't decide on that one! I find items like active crossovers MUST have a shielded case but the GC's seem to be OK without. I also like the freedom you have when you don't have to use a metal enclosure! 
An externally hosted image should be here but it was not working when we last tested it.
If the circuit has gain, bandwidth or susceptability to RF or other interference, it should be in a shielded case. IMO, that's about every circuit there is. OTOH, if you use the right filtering, and apply ground planes correctly, you might get away without, but there's no good reason to do so.
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