Aumkar suggested to apply it with an airbrush, but I simply put a little on microfiber cloth and wipe it on the diaphragm. After it dries, I buff it off. It’s dirt cheap and working very well.
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?