I’ve got my ES2a for a while now. The biggest improvement over the ES1a, in my opinion, is the headband. With the proper clamping force, they don’t fall off my head like the ES1a. So, I ordered the new headband to replace the one on my ES1a. Now my ES1a feels like different headphones. It’s well worth the upgrade. 😄
The hum on my amp associates with the attenuator. On some positions, it’s quiet and in other positions the hum is quite disturbing. I’m using the Alps RK27. Could that be something similar to you?
Have you got the way to align them? Actually it's very easy. You select the objects you want to align. Then you click on the align button on top of the screen. You'll then see the black dots with lines on your parts. Click on those dots and your parts will be align accordingly.
The easiest way to confirm the problem is that you try someway to ground the amp. If the hum goes away, then it's the amp. If the hum doesn't go away, then it's the headphones.
By the way, did you recoat the diaphragms?
I also have hum problems on my amps. In my bed room, there is no actual ground connection. So, I just live with that little hum. Also, please check to see if the problem is from the volume attenuator. On one of my amps, turning the volume knob back and forth changes the hum. At a certain volume level, the hum would go away completely.