Other than the occasional messing around with bias resistors and measuring signal levels on the test rig, not much progress has been made at the workbench. This is because I've instead been designing the chassis, which needs to be completed before any further construction can proceed.
So - after a bit of research I decided on LibreCAD as my design software of choice. It has one (and only one) redeeming feature – its price: free. (As in speech).
Apart from that, this software is a nightmare. Everything works to about 60% and then you have to work around its shortcomings. For a complete CAD virgin such as myself, this proved somewhat challenging. A few times I came close to abandoning the process and instead cutting out bits of paper and re-arranging them on a sheet to simulate the layout.
However, I persevered, and eventually I had some artwork that I was able to send away to be laser cut. This was an exercise in spatial thinking since I was effectively working on the top and bottom side of the top panel simultaneously. A jigsaw puzzle which took some consideration before everything worked.
After the artwork was sent to the laser cutter, a prototype chassis was cut into MDF. Today I have collected this:
Already I have around 10 changes I want to make before the final chassis is cut into 4mm aluminium. This prototype has admirably served its purpose.
Next steps will be actual construction, when the final chassis is completed.