Crack+Speedball Noise [solved]

[somefears]

I've been trying to eliminate a white noise type sound in my Crack with SB upgrade. The noise is pretty wide band, and it is constant (which to my knowledge is the definition of white noise). I would appreciate any troubleshooting advice you all have, because I am about at the end of my rope

 I didn't have the presence of mind to check for noise before installing the SB, so I don't know if it is the crack or the SB. I have gone through and resoldered every connection (maybe not exhaustively), and I have performed all the voltage checks.  The voltage check turned out fine both pre and post SB, except the voltage at terminals 1 and 5 are ~89V, which is a little over 15% the recommended voltage of 75V. I also used Grainger's "Crack Grounding, Signal, and Power Supply" guide to see if all my grounds were properly connected. All points listed in the guide were grounded except for T21, which was basically open (15 Mohms). I also did not have T22 grounded, but I think that is because I used the revised wiring scheme where you connect transformer terminal 4 to 14U instead of 22. I tried connecting transformer terminal 4 to T22 anyways, but that did not affect the noise.

When I performed the resistance check before installing the SB, that passed as well. I didn't see a resistance check guide for the SB. If I am blind and it was in the manual all along, please tell me  .  I have also tried changing the power tube with a Sovtek 6AS7G, which did not affect the noise. I am thinking about getting a new 12AU7 tube to try.

I also performed the chop stick test, with real chop sticks no less. I tapped every component and wire I could see and nothing changed the noise. I was using my high sensitivity IEM's for the test, so I think I would have noticed even the most subtle change.

VERY IMPORTANT: the noise is not affected by turning up the volume.

Other than the slight noise, the amp sounds great. I can barely hear it on my HD 650's, but it becomes pretty hard to ignore on some of my more sensitive headphones.

I have gone through other forum posts regarding noise issues, but none have solved the problem for me. So in conclusion, someone please help this poor fool achieve that black background everyone talks about

[Paul Birkeland]

I'd pop a different 12AU7 in to see if that helps, just to eliminate that from the list.

[somefears]

Thanks for the reply Blackplate. I am going to check with a local guitar amp repair company that carries tubes to see if the have a 12AU7 in stock, otherwise I will order one online. If it doesn't fix the problem, I will at least have a spare. In the mean time, I will continue to bang my head against a wall, I mean i will continue to try to remove the noise.

[Doc B.]

It's either a noisy tube or a honked up transistor. Try a different tube first.

[somefears]

Okay Doc, I'll certainly be giving that a try. I'll post on it later when I get the tube.

[somefears]

The local guitar amp repair place had a 12au7 I could try out, and when I plugged it in, there was no noise! I didn't really like the overall sound of the tube they had, though, so I will probably order one online, but still, no noise! Looking forward to the perfect crack experience 

[Paul Birkeland]

You can also give that tube some time to cook in if you like, the noise may settle out as the cathode is warmed up and left on for a few days.

-PB

[somefears]

Thanks Blackplate, I may try to burn in the tube later, but right now I am currently enjoying the new preamp tube I ordered from Tube Depot. My amp is dead silent with it, even with my high sensitivity IEM's.