A 20kV ESD jolt can easily spark from the metal around the plastic to the shaft.
If I owned an L30 and it still works I would put some wire around the metal screw part around the shaft and connect the other end of the wire to the groundplane.
When the switches also are not grounded I would ground these to the groundplane as well.
Chances are the ESD problems may possibly be solved this way.
Of course the not (properly ?) functioning DC protection is not solved this way.
I fully agree with solderdude here.
According to a schematic of the input circuit, which someone put on the web some time ago, the wipers of the potentiometer go straight to the OPA1612 inputs. This is good for noise reasons, but dangerous in terms of ESD. Especially since the metal part around the shaft is not connected to ground.
If only Topping had used a potentiometer from the RK09L series and connected the ground pins to ground on the PCB.
Some have suggested to ground the L30. This may actually make the problem worse, since it will provide a solid return path for the ESD spark. The ESD spark can easily find a path around the volume knob, hit the shaft, move further to the wipers of the potentiometer with a small spark (internally in the potentiometer or externally) and thereby hit the inputs of the OPA1612.
The OPA1612 has ESD ratings of +/- 3 kV (human body model) and 200 V (machine model), which should be OK for handling what it will be subjected to during production, but far from sufficient if it is hit by a high voltage ESD spark.
I have been involved in a lot of electronic designs, which were tested with 8 kV contact discharge and 16 kV air discharge. This is fairly standard.
It is very disappointing that Topping has not done ESD tests before releasing the product. I agree with JohnYang1997 that the ESD test equipment is relatively expensive, as he wrote "It's neither cheap nor easy to get". I don't think it it too hard to get though and it could be a lot more expensive not to buy it and do proper testing.
I also did wonder about the old fashioned transformer and whether that was leagal at all, as someone hinted at previously. The standby consumption is way higher than it should be.
So where did the CE-mark come from?
I own an L30 and I do like the performance, but these basic flaws should have been eliminated before it was released to the market.
