Monday, 28 November 2016

Home stretch

Today's entry marks the beginning of the home stretch: the chassis is finished and the assembly work has begun.

I estimate I'm going to need two to three full days to complete the assembly, likely including a few trips to the electronics store to collect various fasteners and such like, before the job is complete and testing can begin.

Just to satisfy myself that I'd done something, I began assembling a few components onto the chassis, pleased to say everything seems to fit; the holes all line up and are the right size (so far!)

This amplifier will contain TWO mains transformers: the large main transformer, and a smaller one to provide 9v AC which will be the standby power. This transformer will power the input selector, remote volume control and standby control, and the chromecast USB power supply.

Having two transformers allows the provision of the full remote control, including power switch.

So the top plate of the chassis will need to support the mains transformers and the output transformers. It's made of 4mm aluminium and it seems equal to the task without bending, based on some benchtop tests. Time will tell if it starts to sag in use

More pictures and progress reports as assembly continues. Some quick phone snapshots for now.

Power Supply, USB supply, rear terminals, volume control and rotary encoder in place

The back panel. Note switched power output – this will run to the separate (valve) phono preamp.
Outputs will be 4 and 8 Ohm.
All these separate panels are gonna need some heavy-duty earthing!

Tuesday, 22 November 2016

Lots of holes

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.