I've recently completed a Crack build with Speedball and sold it to a headphone aficionado that lives very near to my home. I'm glad he lives so close, because we keep having problems with the Crack.
I built it, tested all the voltages, listened to it for several hours over a period of nearly a week before I sold it to him. Everything was working perfectly. He came and picked it up, I got text messages saying that it sounded great. Then the next morning he texted again to say that there was a loud crackling and popping in the left channel and that he was afraid to plug his headphones in again in case they might get damaged.
He brought it back to me and I looked it over. Sure enough, it was making noise and I tracked down the problem to a ground wire that I thought was connected but actually wasn't. I also spotted a few solder joints that looked a bit iffy. Heated up the soldering iron and five minutes later it was fixed. No more noise, so I had him come pick it up.
He reported back later that everything seemed ok. Meanwhile, he had asked me earlier to do the volume pot resistor mod from the Crack FAQ. A few days later, those resistors arrived and he brought it back to me to do the mod. After the mod, everything sounded great and was working as it should. He took it home and reported back that he was thrilled. Sounded fantastic.
The next morning, I got a text saying that the Crack was making noise again. This time in the right channel. It was a faint static sound that seemed to start as the headphones were plugged in and last several minutes then go away. If he unplugged the headphones and plugged them back in, the static would return.
So he brought it back to me again. I listened to it for a couple hours that night and couldn't get it to make the noise he was describing. Sounded perfect. Tried it again the next morning and still couldn't repeat the problem. I let him know, he picked it up and took it home and reported back that I was right--no noise.
The next morning, I got another text saying that static was back. This time I went to his house to listen to it in his setup. I heard it this time. Faint but clearly audible static in the right channel when the plug was fully seated, but as you pull the plug out a bit static can be heard in both channels.
When we were at his house and I could hear what he was talking about, we tried different tubes, different interconnects, with interconnects connected and without. He's got it plugged into an APC uninterruptible power supply. We unplugged it from that and plugged it directly into the wall. Nothing seemed to have an effect.
Flummoxed, I took it home to have another look and figure out what's going on. It's on my workbench now, and guess what? No static.
Any ideas on what I should be looking for?
