I completed the crack w/o speedball. Tested it for few weeks, with no problem sounding great. But after few weeks of use I started noticing a hum. did not use it for a while, I then used two different DACs and even moved it away from speakers and wifi, tried laying the crack on the floor away from everything. The hum persisted, I always start from 0 volume but just at 7o' clock I start hearing the hum. It's too loud to bear. I switched back to my solid state headphone amp, I don't hear the hum that I was hearing with the crack. Hope it is just a minor problem