I just finished my first ever build, it worked the first time when I plugged it in too, thanks to the really good instructions on this thread. If anyone's just staring out, like I did, I recommend they pick up DIY synth kit to practice with - they're dead cheap and they teach you not to make mistakes with soldering.
Anyhow I'm now stuck on calibrating the VU meter. I have to idea what to do here. If I set the Test Oscillator in Logic X to make a 1KHz sine, at what level do Logic 's output meters need to peaking at?
Switch the comp to VU and put in a 1kHz tone until you measure 1.23vac between pin 2 and pin 3 of the output XLR of the LA500 rack slot. Then adjust the VU trimpot for 0VU.
You can also measure the 1.23vac between pin 2 and pin 4 of the LA500 edge connector