I did some testing this morning, and it looks like some counterfeit transistors made their way into our inventory. We will be shipping out replacements when we receive a replacement batch shortly.
Just wanted to add a second case. I have exactly the symptoms described by the OP and have gone through the same exercise and have isolated the issue to the two small PCBs. Currently back to the 22.1k loads and the large PCB. Not sure if it's placebo, but with just the large PCB I can already hear a significant improvement in the sound (on HD 650). There is far less veiling and the sound is brighter. The mids are singing, although were great, now the highs are almost as clear as the mids. Bass is deeper. There is only an ever so slightest background noise at max volume.
Details:Ordered on the 14th of April, shipped May 14th. The vanilla Crack worked on first power without a hitch (thanks for a fantastic product and an amazing guide). The sound was actually better than I was expecting (first Tube amp, was expecting higher harmonic distortion, background noise, and rolled-off highs... none was true).
After upgrading to the Speedball, I had an annoying buzzing without having a source (on connecting a source does play the music, but the buzzing is very audible throughout). All voltages were within range (<10% of the ratings). LEDs all light up as expected (after a few seconds, the 2 on the 9pin socket and those on the small PCB light up rather quickly, then slowly the ones on the large PCB come to life and are brighter than all the others). The buzzing sounds like 120hz and it's loud even on lowest volume. It actually goes quieter when I turn the volume knob (but never acceptably quiet,) until I hit past two thirds, then it's loud again. I resoldered all joints, no help. Quadruple checked the circuits, all look good. The warm-up DC on the jack climbs past 20 and hits high 30s. Without Speedball it never crossed 15V.
The buzzing is worse where there is WiFi. Away from WiFi source and simply moving my hand around the small PCBs make the buzzing volume changes significantly. Furthermore, touching the chassis or the pot changes the buzzing as well (touching the RCA changes nothing). Clearly the small PCBs are picking (and amplifying) RF, or at least the buzzing is modulated by RF. I can't verify the authenticity of the 2907, but I'll mention that their package sizes are different (one is shorter than the other).
After removing the small PCBs and resoldering the 22.1k loads, the background is very quiet, no buzzing or other noise.
Please let me know what I need to do to get replacement parts or other remedy to fix the issue. Although I'm very satisfied with what I have now, I'd like to get the full shebang.
Thanks again for a remarkable product!
