Effects of chassis material

[mike3124]

My curiosity is piqued by the question of what the effect of a non-conductive chassis (wood, plastic etc) would be on amplifier construction.

OK if you have heavy transformers etc then steel makes sense but for smaller amps is metal necessary?

[Enzo]

You would lose the shielding the chassis provides.

Notice the space in your guitar for the innards is generally lined in foil or somthing, and the cover often has a ground connection. And even for metal amp chassis, note how the open side is usually covered by a metal sheet or aluminum foil or metal screen, which then ground themselves to the chassis when it is bolted in. These are to complete the shielding left gaping on the open side of the amp.

[Don Moose]

You could, of course, line your wooden or plastic box in foil or gutter flashing, but the places where jacks and knobs poke through are so much stronger in metal than plastic or wood - unless you get the material thick enough that you have to buy special long-shank pots and jacks.

Hope this helps!

[Merlinb]

OK if you have heavy transformers etc then steel makes sense but for smaller amps is metal necessary?

I have seen people build small amps in plastic boxes (ABS). In lowish gain, low-power applications external noise pickup isn't always a big issue. Certainly a cheap way to experiment with small circuits!

(I even saw someone on a forum post pictures of an amp he built in a CARDBOARD box!! I certainly wouldn't recommend that, if only for the fire hazard...)

[murraym3]

Wouldn't it affect ground potential?

[Enzo]

You would have to run ground or common wires through the circuit. You could not of course use the chassis as a ground.

[rathmann]

If some kind of plastic material was used you'd also have to be somewhat wary of where the heat will go. A Fender-style hang-the-tubes-underneath arrangement might cause the chassis to melt! I'm not real familiar with the properties of the various types of plastic so maybe one could be found that would be tolerant of some heat.

[Enzo]

Find some ancient bakelite.

[mike3124]

Thanks everyone. I guess the screening and grounding arguments are pretty good. I did some more thinking about it lining plastic top and bottom with foil creating a giant cap, mechanical problems etc etc.

I was wondering about reducing weight but I guess if it's an amp of any size (especially tube) then the transformers create most of the weight anyway.

Thanks again for the thoughts

Mike