Why doesn’t Sony ground 4.4?

Far before Astell&Kern finally popularised the 2.5mm socket on their DAPs, the balanced system in a portable system had already had a very long history. Even though the 2.5mm is very popular in usage, the market is not that satisfied because the 2.5mm cannot be grounded as a “real” balanced system should be. This explains why the market was so hyped when Sony first brought to us the now mainstream 4.4mm Pentaconn connector on WM1Z and WM1A.

Again, only disappointment awaited because the Pentaconn connector was not grounded (GND) either. Some people think that perhaps it was just a more cautious approach to the balanced system because the 2.5mm has never been grounded, too. The WM1 series is just a small stepping stone to where we will see a fully grounded balanced system, just as the home audio market.

Now, the 4.4mm Pentaconn connector is mature and dominates the market. Sony, after 5 years, brings to us the 2nd generation of the WM1 brothers, still leaving the 4.4mm ungrounded. Why?

We can discuss some possible reasons.

1. There is no “real” GND in portable systems.

GND in a portable system simply means 0V, not the Earth. Some engineers just want to avoid drawing noise from shielding because the noise will not be drawn to Earth, but it interferes with the board.

2. Balanced cables need not be shielded?

Some engineers believe that a balanced system already cancels out noise, and shielding it does not do us any good for noise cancellation. It usually backfires indeed, because it affects the structure of the cable and the energy spreading around, as well as the impedance of the cable. It is common that cable makers (DIYers or manufacturers) found that sound can turn bleak and dull, and that quality deteriorates significantly if the cable is shielded. It makes perfect sense for an engineer to choose not to ground the connector if they have that experience. (A friend once asked me how to get rid of all those negative effects. “Well, why just don’t shield it?” I replied. His answer was fair enough, “People just love shielded cables. It makes money.”)

3. Never ever ground the shield/connectors?

Once a friend who worked in the engineering department of the platform screen doors (railway) told me that there is a PCB with ungrounded connectors in the system. The manufacturer confirmed that that was the correct setup and they could keep it as it was. He was confused because it was such “common sense” to ground the shield of a system.

I am definitely an amateur to their projects, but I told him not to worry at all. It is completely fine to not ground the socket. Rick Hartley, a leading figure in the electronics industry claims the shielding of cables must not be connected to the internal ground. It contradicts and offsets the purpose of shielding by pulling in external energy into the system.

He said, “ Never ever attach the shield to the internal ground that is absolutely the wrong place to put it. Because you’re allowing any energy that couples on the outside of the shield to couple right though the opening in the box and couple right into the ground structure of the board.”

He further added that this is valid only if the system is well-structured, otherwise under some circumstances there is no choice but to ground the shielding on one/both ends.

Which is Sony’s true consideration, or is it something else that we never think of?