I have built my Crack without speedball yet and it's totally awesome. I was curious how turn on/off transients look like, so I took a couple of oscilloscope measurements. One through 330Ohm resistor, the other without. These transients look pretty good, I would think this can't harm hd800s. One thing that has to be noted is that the turn on transient happens 10s after the switch is flipped and lasts for 5 seconds. The turn off transient happens instantly and also lasts 5 seconds. So to be careful you have to wait for at least 20 seconds before plugging the headphones in when turning on and 5-10 seconds when turning off. Here are the measurements if anyone is interested.