DIY 1176: The build begins

On September 7, 2013

On Wednesday, I found out how addictive building these projects can be. As soon as my regular working day finished, myself and my colleague Ludo Morin cracked out the parts for the DIY 1176.

The first task was the power supply. I’ve already previously talked about the confusing toroidal transformer not being the same as the manual, so this was the first mystery we needed to solve. After stacking the serial windings and checking the secondaries, everything measured fine. After I connected it to the power switch, everything got a bit weird. + and – were both seeing each other when we ran a meter across them. Apparently this is normal as the two windings are combined, and the 25v secondaries haven’t been soldered to the PCB. We plugged the unit into the mains and I’m still alive to type this, so looks good so far.

Mounting the toroidal for the DIY 1176Connecting the toroidal to the IEC and power switchEspresso top-up after testing power supply

We cracked out the tin of components and began on the PCB. None of the resistors are marked, so the first task was deciphering which was what. Rather than translate the colour codes, it was easier to just tape them all down to a sheet of paper and run a multimeter across them, measuring the resistance of each. Then you can just pull them off the paper as and when you need. After lining up the rest of the components, Ludo got to work dotting solder across the bored. After several hours working on the PCBs and drinking espressos, the potentiometers were mounted and wired, finished off with the shiny knobs from Farnell.

PCB for DIY 1176Components for DIY 1176Lining up the components for the DIY 1176

With two pairs of hands, wiring the potentiometers while mounted was a pretty simple task and meant we could just solder them in their positions. If you’re on your own, I’d suggest using clamps here, or wiring the pots first, then mounting. I wanted to do a really tidy wiring job, so it was easier to figure out the cable lengths with it all in position. In the excitement of it all, I forgot that the pots needed to be cut down so the knobs could sit properly. Taking my very sharp Leatherman saw, I proceeded to GENTLY saw the pots down. Don’t be too aggressive doing this as you can damage the contacts in the pot itself. And don’t let it slit and lop off chunks of skin from your thumb, like I did :-/

Office doubling as workbench. DIY 1176 Case with PCB and wired potsFront of DIY 1176 Case with PCB and wired potsTop view of DIY 1176 with PCB and wired pots

┬áLastly for this session, we worked on the grounding. I had to drill a hole in the rear chassis and buy a grounding post from Maplins to ensure the toroidal and XLRs were all going to common ground. After 8 hours of soldering and a bit of testing to ensure all was going to ground correctly, it was time to wash up the coffee mess and clean the blood of my fingers (nice…). Once the Lundahl transformer and Sifam VU meter arrive, a couple more hours to solder all the connections to the PCB and test the circuit should be enough before putting the unit through its quality tests.

More updates soon…


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