Before I actually finished the electronics design, I already started constructing the cabinet. To give you a sneak preview of what it will look like, the pictures below show the cabinet while still under construction and the front panel design. I designed the front panel layout in Altium. Not because this is the best software for this purpose but just because I’m familiar with using Altium. I first tried to design a front panel in a dedicated freeware program I downloaded from the internet, but I couldn’t get used to the user interface. So far for now on the front panel design. I will get back on the front panel later.
As I was unable to find a suitable standard case, I decided to design a cabinet myself and construct it from wood panels and 15mm aluminum corner profiles. I lack the tools and skills to build an all-metal case, so I chose to use materials I could easily process and some of which I happened to have at hand in my workshop. In the top half of the cabinet, I sandwiched the PC between the roof panel and the “2nd-floor” panel. The bottom half of the cabinet holds all the other electronics, including the Audio Interface, front-end and output driver electronics, power amplifier, voltmeter and the inevitable power supplies. In the pictures, you’ll see the bottom of the cabinet tiled with two 19.5V laptop power supplies powering the power amplifier, LM3x7 based 5V and +/-15V linear supplies and the 48V phantom power supply. On the front side, at the right, you’ll see the TDA7293 power amplifier module.
To avoid interference and hum pickup, the power supply transformers were placed as far away as possible from the most sensitive input, which is the microphone input. The mic input will be located at the front left, so the transformers were placed all the way to the back and to the right. For the same reason, I also placed the power amp on the right side of the cabinet. And to avoid hum and RFI from external sources, I lined the interior of the bottom cavity with aluminum foil. The foil connects to the aluminum profiles on the corners of the cabinet.
The “ceiling” of the bottom cavity holds the mains power distribution PCBA and mains wiring to the power supplies. The Audio Interface will also be suspended from the “ceiling”, somewhere in the middle. All the wiring to the input and output circuits and the Audio Interface signal LEDs will exit from the backside of the modified Audio Interface. This side will face toward the front panel, where all the front-end electronics will reside.