The whole point to adding mass to the top of any case is to reduce vibrations from the somewhat flimsy case metal. You could also do that by placing some sticky damping materiel inside the case itself, under the cover and under the circuit board on the bottom, if there is room. I just wouldn't do this if there is heat being generated. You may find some room for that away from the tube but definitely use something that won't scorch or melt.
Bob,
I appreciate your input. I did that on a few items years ago. Don’t have the damping material any more. My Border Patrol dac is very solid and heavy for a small unit. It has a copper chassis as I understand it.
If I were knowledgeable enough and/or inclined to do so, it would be interesting to measure the effect of simple weighting vs using a damping material. The unit generates very little heat
http://www.borderpatrol.net/images/DAC%20Pics/DAC-Wht-Tab-350%20Col%20Adj.jpgJust found part of this interview that applies here...
Doug Schroeder: The DAC SE uses copper for chassis. Why?
Gary Dews: The use of copper for the casework was a spin-off from the Border Patrol amplifier designs. Early BorderPatrol amps were made with steel and aluminium chassis. There was a noticeable difference in sound between the two. Steel imparted a glare and grainy character to the sound. Aluminium, by comparison, sounded lighter, freer and airier but was also somewhat frenetic and unruly by comparison. I was lucky enough to hear amplifiers made by Audio Note Japan and to meet the legendary late Mr. Kondo several times. We discussed amplifier design and I asked him why he used copper for the chassis of his amplifiers. He told me it was not for looks and that copper sounded better than steel and aluminium. He spoke about calmness, tone colour, the quietness of background, noise floor (audible, not measurable) and freedom from grain. I had a copper chassis made for my amplifier and the difference was clear. When I realized I could use copper casework for the DAC and still make it relatively affordable it seemed like an obvious thing to do. Anyone that thinks the chassis material does not play a part in the sound of a product hasn’t done the work.