I have been doing internal layout work and making some design decisions concerning the new SET amplifier. I have also been looking at different materials and I decided that I wanted to make the top plate holding the transformers and tubes of brushed copper. While this is an simple decision to make at this point, it raises the issue of what wood to choose for the chassis frame.

When the top plate is painted a color, or is simply black, the choice of wood is not too difficult. If black, just pick what you want. If colored, just find a wood with a comparable tone. However, in the case of brushed copper, the decision is much more difficult.

I made this decision when I was building the 6DJ8 Headphone Amp although in that case the choice of wood came first. The copper was chosen as an accent. And in that case, the wood clearly dominated the appearance of the amplifier. With the new SET amplifier, the big piece of copper on top (12″ x 10″) is going to be very dominant and make a strong statement; as will the blue of the transformers. This makes the choice of wood more difficult.

Well, I have narrowed the choice down to six candidates. These are shown below:

From right to left left to right (Oops. Sorry about that) these boards are Bloodwood (fine grain), Bloodwood (coarse grain), Purple Heart, Wenge, Bubinga, and Padauk. Each of these has a unique character and could achieve a nice balance with the copper. It is also good to remember that these are all raw wood and will be slightly darker and richer when finished with an oil finish. But the real question is how to decide.

I took a sheet of the copper out and laid it on the various boards. I have a couple of pictures of this.

This is the copper sheet laid on the Bloodwood, Purple Heart, and Wenge.

And this photo shows the copper with the Bubinga and the Padauk.

Personally I rank the Bloodwood last. There is something about the tone that is too close to the cooper sheet. I fear that the similarity would detract from both. I really like the Purple Heart and the Wenge but for different reasons. The Purple Heart is a great color accent with the copper whereas the Wenge is a strong contrast in tone. I think either would make strong statements.

I am less enthused with the Bubinga. I know it will darken with the finishing, and the grain will be striking, but the tone is a little close to the copper. I am afraid that the fine grain and figure will get lost when paired with the copper and the amp will look monochromatic.

Last is the Padauk. The important thing to remember about this wood is that it changes color strikingly with time. When freshly milled it is almost bright orange. But with time it oxidizes to a rich red/brown color with strong grain variations. The only problem with this is that I have to build on faith, because it will take as long as a year for the amp to achieve its true tone (from a perspective of appearance).

Ok, I know that strictly speaking, this is not about electronics or vacuum tubes. But it is about amplifier design. So I’m asking for some input. I’d really like to know what people think. Am I on the right track? Is there one choice that really stands out? Is the idea to use copper a bad one?

I really am curious what people think. Please let me know in the comments.