I just saw the post about bootstrapping our access to space via Slashdot and after a long upsetting day at work seeing this and thinking about what it means puts my day (and week) into perspective and makes me feel a little better. It’s likely that none of these ideas are original and are obvious but I wanted to take the time to send an email even if all it is is just a vote in support of the goal.
After a bit of a long delay I’m going to call this finished. I knew it was all working but it had been in a a testing phase for too long so I made a big effort to get the thing done. I’ve redone a lot of the internal wiring and put the front and back panels on. These are made of an old server lid and are galvanized 1 mm steel sheet. I had to cut the strips with a cutoff wheel in an angle grinder so I could then use tin snips. It would have better to use a guillotine. Steel is I think better than aluminium, it is stronger and I think it works better at shielding. When I was testing the amplifier with the computer prior to finishing the panels I was getting some kind of electronic noise coming through, now I get nothing. (I presume it must have been the graphics card that would generate audible harmonics because the rest of the computer would generate signals outside the audio range).
The main heat sinks are made from an old industrial air conditioning controller. The heatsink on the bridge is half a heat sink for some old cpu. Note that the transformer from the old receiver is shielded, it seems to be very quite. The only issue is that I have no idea of the VA rating of the thing.
I had to do a fair bit of hacking around on the front inner panel due to my not measuring properly where the pots and the audio were going to protrude.
I’ve also replaced the old power switch with a DPDT and included a mains filter (no idea if that is needed) and a mov directly onto the IEC plug. The speaker / headphone switch is another 240v switch of about 16 A and to the left is the resistor network for the headphone output. I tried to make all the wires use plugs to make for easy repair.
The heat sinks for the power amp chips are insulated from the chassis so I need no washers between the metal tabs of the chips. This means the heat sink is at about -ve 30 something volts I think. I tried to make the wiring as neat as I could and separate the blocks of function so the inputs are at the front of the amp near the pre-amp and the speaker plugs and headphone socket are along the back. This means the signal travels from low to high around from the front to the right and then through the power amp and then to the rear. 240 v is along the lhs edge and the DC is over to the left.
This is what it once looked like.