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Non-metal Chassis
http://diyaudioprojects.com/Forum/viewtopic.php?f=14&t=4581
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Author:  RossD [ 04 Nov 2013, 08:56 ]
Post subject:  Non-metal Chassis

I've seen a few builds on here that do not use a metal chassis. Personally, I'd like to work in wood. It just seems to be a bit more forgiving. They can have their own hurdles, however.

Is there any safety concerns to consider when you don't have a large chunk of metal? What would I have to exclude/include to the build? Should there be a ground plate or can I run a buss or bare ground lead?

In my head, it's no different to replacing the metal chassis grounding points with a bit of wire in a non-metal build.

Thoughts? Concerns?

I did a search to find any other relevant topics but didn't come up with much, so if this has been covered, links will appreciated.

Author:  Gio [ 06 Nov 2013, 19:16 ]
Post subject:  Re: Non-metal Chassis

Hi Ross,

What sort of electronics are you looking to enclose? Tubes are special and so are high gain electronics. Shielding is likely one item you may need to add.

Here are a couple of threads with some info:
viewtopic.php?f=14&t=1565
viewtopic.php?f=14&t=2346
viewtopic.php?f=14&t=557

Cheers

Author:  RossD [ 06 Nov 2013, 21:47 ]
Post subject:  Re: Non-metal Chassis

Sorry, I meant to refer to tube power amps and tube preamps. Thanks for the links, Gio. I will take a look through them.

Author:  Gio [ 06 Nov 2013, 21:55 ]
Post subject:  Re: Non-metal Chassis

You can use wood (not MDF) with tubes. Heat tends to build up easier so you have to give ventilation good consideration. I like to use aluminum tape on the inside for heat protection and for shielding.

Cheers

Author:  gofar99 [ 06 Nov 2013, 22:00 ]
Post subject:  Re: Non-metal Chassis

Hi, I have used all wood and all plexi chassis from time to time. There are no particular safety concerns that would not already apply to any sort of tube gear. The main issue is noise (EMI) pick up and hum pick up. You may need to shield some sub assemblies in metal enclosures. Any circuit that has gain of over about 10 or deals with signals much below 0.5 volts is likely to need shielding. Power amps usually will not, but preamps other than low gain line stage ones probably will.

Good listening
Bruce

Author:  RossD [ 07 Nov 2013, 08:39 ]
Post subject:  Re: Non-metal Chassis

Thanks guys. Yeah I would probably make an all wood (pine or oak for now) chassis. For the aluminum foil tape or small metal enclosure, do you ground them all together back to the star ground?

I suppose you have to watch out for strips that touch each other multiple times and make for a ground loop?

Author:  Geek [ 07 Nov 2013, 09:02 ]
Post subject:  Re: Non-metal Chassis

My experienc with all wood chassis....

Heat...
Cool...
Heat...
Cool...
[some time]
Heat...
Cool...
*CRACK!*

So, I put the things that heat up on aluminum and have wood all around.

So Gio, why not MDF? I've repaired/modded commercial gear in all MDF boxes and they seem just fine :confused:

Cheers!

Author:  gofar99 [ 07 Nov 2013, 09:32 ]
Post subject:  Re: Non-metal Chassis

Yes the shields should go to the star ground and not touch each other unless that is the path to the star ground. Ground loops have ruined many otherwise good projects. For shielding some things I have found that you can get cast metal boxes either designed for component use or from the hardware store for use in electrical systems. The ones for electrical systems often have mounting feet. Look in the early Forewatt project - I used one in the first version to house the power transformer. That is an all wood design and the mounting feet makes the boxes easy to use in all wood chassis. In that particular build I didn't shield the audio as the gain was so low. Later versions do as it does help shield from EMI. I had a problem with nearby electrical gear that forced the change.

Good listening
Bruce

Good listening
Bruce

Author:  Gio [ 10 Nov 2013, 11:28 ]
Post subject:  Re: Non-metal Chassis

Geek wrote:
So Gio, why not MDF? I've repaired/modded commercial gear in all MDF boxes and they seem just fine

I find that MDF really traps heat. Prob fine for a very open guitar chassis but most hi-fi chassis are pretty closed up.

Cheers

Author:  mwhouston [ 12 Nov 2013, 08:46 ]
Post subject:  Re: Non-metal Chassis

The only time a had a problem in a nonmetal box was with a phono preamp. I could not get enough shielding to stop hum. I use a bituminised heavy sticky Al foil to line most builds, metal or not. Even with this AC mains hum got in when the device was battery powered.

Amps and preamps (line level) should have no problems. Still line them with foil.

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