I had the preamp, power supply, and fake op amp boards made by PCBWay. The power supply board doesn't have the filter caps or regulators because I built it before the enclosure came. I had no idea if the regulators needed to mount vertically, above the board, or horizontally below the board. Once the enclosure came, and it had the divider wall for the power supply, I added the regulators. After the mounting holes were drilled, I added the capacitors.
Almost all of the electronic parts came from Mouser. I bought enough parts to build 2 sets of boards, just in case. Other parts came from ebay - fuses, standoffs, and the TO-220 mounting kits for the regulators.
The 990C+ op amps came from ZenPro Audio. I also got a pair of SK99 op amps from Sound Skulptor. The SK99s come in kit form, but the documentation is clear and concise. The first one is a little hard, but the second just goes together. And lastly, I made a pair of op amps with the same footprint, but using OPA134 op amps. I figured if I mis-wired something, it's better to burn $5 than $50.
The power transformer, from Antek Inc, provides 22VAC @ 50VA. The transformer bottom mounting bracket was hard to find. The transformer is around 93mm in diameter. The closest sizes I could find were 90mm and 96mm. When they arrived, they were both 96mm.
The chassis came from FunKenya World Store. It is unbelievably well-made. There is a separate section 120mm wide for the power supply (not really shown on their website). Every one of the screws fit without wiggling or applying pressure, and the panels fit perfectly. And it's heavy. I also bought the input switch board from FunKenya. The input switch board has a rotary switch on the front panel, and the relay board on the rear panel, with a 580mm flat cable between.
The hole in the front panel where the pot goes needed to be reamed a little. The threads on the stepped attenuator are 3/8", the hole was just a little smaller at 8mm. The input selector hole was the right size. There is a hole for a 3mm LED behind the front panel, above the power switch, with a smaller hole on the front of the panel.
The power supply work was just to place the transformer, and do the AC wiring. I used a piece of flexible terminal strip to tie the AC to the transformer primaries.
All done. See the preamp page for more on the project. The finished unit, as empty as it is, weighs 12.4 pounds. It's the enclosure, or at least 9 pounds of it is.