Friday, April 18th, 2014 | 11:05 pm and filed in Gear.
This is yet another one of the various nightmares one can encounter when dealing with audio hardware. While patching my Eurorack modular rig into a tube mic pre, I felt the light buzz of an electric current passing through my fingers. Obviously, this is not a good sign, and it means something is terribly wrong. After disconnecting everything except power, I tested for voltages across grounds and discovered a 120V AC difference between the tube amp ground and the Eurorack case. As it turns out, the problem was the IEC power cable… yes, that unassuming three conductor cord that connects to the power main was at fault!
A continuity test revealed that this cord is essentially cross wired. This means the Neutral from the mains is connected to the Load of the IEC connector and the Load (Live wire) from the mains is connected to the Neutral. In the photo above, you can see continuity between the Load contact and the Neutral on the IEC connector. Even with the synth switched off, power was running into the system, and a bit of current was finding it’s way to the panels and case.
Unfortunately, I have no idea how this cable was acquired. It was just in the box of power cords, and presumably correctly assembled (how the heck can you mess up 3 connections?) The cord is labeled, “PVC YOUZHI DIANXIAN 3C RVV 300/300V,” and it’s missing the country of origin. A quick websearch reveals that it was manufactured in China, and YOUZHI DIANXIAN is known for other substandard cable products.
The good news is that the synth and tube amp are fine, but i ran into problems with some other audio gear. A few components are blown (again) in my monitor control system, and I need to check on some vintage compressors. I’m just lucky that it didn’t cause more severe problems like data loss or death :-/
Cable has been properly destroyed, and is ready for recycling! Moral of the story: always use the IEC cable supplied with the gear or test the contacts to make sure they are not crossed before you connect to the mains.