Hi everyone, hope you're all staying safe. I bought a Crack around a month ago after reading about it and researching it for a week straight, everyone had good things to say so here we are.....after finishing the amp I tested it straight away and was thoroughly blown away, until about 3-4 hours after listening, I heard a slight crackling in the left channel. It got progressively worse, I thought it needed burn in, so I left it on for 8 hours overnight with music playing softly and a very gentle breeze to help keep it cool. The next day I had a quick listen and the crackling was still present. I thought it still needed burn in so I put about 20 hours of actual listening on it, somedays it sounded totally fine, a couple of days it crackled as soon as it warmed up and the crackling would come and go totally at random.
The crackling is only in the left channel and sounds like dust on an old vinyl, the right channel didn't have any crackling until after I tried to fix it (get to that in a bit)
I spent an entire night troubleshooting and took the following notes:
1/ Crackling does not change volume when volume knob is adjusted.
2/ Crackling does not change if RCA cable is plugged, unplugged or swapped over.
3/ Crackling does not change with different source device (Sony ZX300 and Samsung Note 9).
4/ Crackling does not change if connecting my Sennheiser HD600 via (official) single ended or balanced cables with a convertor.
5/ Changed power cable, still crackles.
6/Used different powerpoints in the house, with and without a filtered powerboard, still crackles.
7/ Tried two other 12AU7 tubes from my xDuoo TA-20 amp, still crackles.
8/ Tried different headphones altogether (Focal Elear, single ended and balanced to SE convertor), still crackles.
9/ Wiggling and tapping tubes while amp is on makes no noises or popping. so I'm guessing things aren't loose.
10/ Tapping all over the amp produces no pops or additional crackling either.
11/ The crackling isn't radio interference as I tried three different places in my medium sized house, as per point 6.
12/ Crackling only occurs when Crack is fully warmed up (when music plays at regular volume).
13/ Unplugged and plugged in both tubes numerous times in case of corrosion in terminals or tube pins, still crackles.
14/ I have tightened the transformer screws as suggested in other forum posts.
15/ I have reflowed ALL solder joints TWICE, some of them three times, especially connections pertaining to the left channel, from the black RCA jack, to the volume knob, to the tube sockets, to the headphone jack.
16/ The two red LEDs on the 12AU7 socket light up and do not flicker, even when tapped
17/ I have tightened the screws on the 12AU7 socket clamp as suggested in forum post.
Regarding point 15, I have done the following:
a/ Every single solder joint has been reflowed. Every single one. Twice.
b/ Both tube sockets have had all their solder reflowed three times.
c/ Every solder was done by tinning the soldering iron, then applying heat to both the component/cable and the hole it's going through, then letting it heat up for a second and applying solder.
d/ None of the solder joints are loose, or cracked, I have wiggled every single one of them with needle noise pliers.
Guess what? Now the crackling in the left channel is even worse, and now both channel hiss whenever it crackles too! What have I done wrong, I'm at wits end. The only thing I could not test was swapping out the big tube, could it be damaged, or have I heat damaged something?
