Ground Mysteries Sparkler DAC Connection Issue

Letter from Hong Kong (20-14): Ground Mysteries

Although for the longest time I have always had multiple systems and all sorts of things running at the same time (higher chance of ground loop), it is not often that I have hum problems. Occasionally turntables would put me to work but it could always be worked out. But two recent incidences are highly puzzling.

1. It is well known that power connections can be a problem. Although 3-pronged IEC sockets and plugs are the standard, many equipment actually don't connect the ground or join the ground with neutral. All vintage equipment and most Japanese equipment are two pronged. You can imagine someone like me, who mixes all kinds of gear, to be vulnerable to ground issues. Also, the usual advice is to have everything coming off one outlet, but that's not possible for me, who runs multiple stations all over the room. It is a miracle that I don't usually have problems.

Except for my Wavac MD-811's selector, which has a contact problem. One channel would sometimes cut out or hum, and it would take some wiggling to redress the issue. I tightened the nuts of the selector and volume pots but that did not help. One day, while it started to hum again. I was at Station II, where I was installing something. For lack of a power cable I pulled the one on a piece of idle equipment (no standby circuit and not drawing current). Immediately the hum stopped. Weird? Well, I kept that power cord out of the system. I didn't have enough time to test more since I was about to leave NYC.

I chatted about this with Andy. He said he frequently had issues with the 3-pronged power cords and had to use cheater plugs to float the ground (reason why some equipment has a ground switch to allow one to do that). He also maintains that if every thing is 2-pronged there is a lot less chance of hum.

2. This one is positively bizarre. Long time readers know that I love my Sparkler S-306 DAC. But my unit has a quirk - it'd not accept many digital cables (as reported here). I took this cable to NYC and recently tried to use it with intermittent success. More often than not, it would not work, issuing crackling sound. Now, I didn't report this before, in HK once when I pulled out a digital cable from this unit, the hot pin accidentally touched the collar of the female connector, and to my surprise I heard music for that instance (I had the volume knob down, but not off).

When I returned to the audio room, I tried to install the S306 again. No success with all my cables. I then tested it by pressing the hot pin against the female collar - perfect transmission. So I took out my solder and reversed the two tiny wires to the circuit board, and it worked with all my digital cables.

Is that not weird? If the wires had been reversed, how come it would (often or sometimes) work before the surgery? Is there a grounding issue here? I don't have the answer.