Transient crackle only in right headphone

[Chase_adams]

I apologize in advance if I'm posting this in the wrong section. I recently (about a month ago) built a crack with speedball upgrade. All voltage and resistance tests checked out (I made good and sure they did before even attempting to use it). In the last few weeks there has been a light crackle sound that appears only in the right headphone. At first I thought it was maybe it was just a bad recording that I was listening to, so I paused the music, but still the crackle went on for another few seconds. It generally only lasts anywhere from 5 to 10 seconds and will then go away. Usually it'll come back at least every 3-5 minutes of listening. Any thoughts what this could be? It seems strange to me that it will come and go. It's definitely not the headphones because I've tried two different pair (HD 650 and HD 800 S). Any help would be greatly appreciated. Thank you so much!

 

[Paul Birkeland]

A noise like this can have several causes, and I'll list them in the order of how frequently we see each issue:

1.  A flaky solder joint:  If a joint is well crimped but not well soldered, it may make noises at random intervals.  The best way to check for these is with a cheap pair of headphones plugged into the Crack and a wood chopstick.  When you poke the bad joint, you'll get a pretty loud pop.  The most common joint that I see causing problems is where the black wires meet on the headphone jack.

2.  Dirty tube pints:  All 6080s are reasonably old, and we supply old stock 12AU7s.  Sometimes the pins can get a bit oxidized, and dirty tube pins can cause some noise.  The easiest way to resolve this is to pull and reinsert each tube several times to scrape through the oxide layer.

3.  Loose hardware: This is a frequently overlooked aspect of these builds.  The hardware needs to be tight, and it needs to be consistent with what's in the manual.  The frequency of improperly mounted power transformers was one of the major reasons for the Crack 1.1 revision. 

4.  A noisy tube:  You'll notice this is last.  Occasionally, we find a noisy tube or two.  Almost always we can get these tubes to quiet down by letting them run for a few days straight, so this is unlikely to apply to your scenario. 

-PB

 

[Chase_adams]

Ok, so I've tried everything you've recommended and I am still getting the noise in the right headphone. I found no bad solder joints when using the wooden chopstick method. How would I go about getting a replacement set of tubes and sending back the ones I currently have?

 

[Paul Birkeland]

Have you let the Crack sit and run for several days straight?

 

[Chase_adams]

I am currently letting it run as I write this. It's been on for about 15 hours straight now. I will let you know if the noise persists after 24 hours.

 

[Chase_adams]

I was able to try a different 12AU7 tube today, and it turns out that the tube is the problem. My friend described the tube as a "microphonic tube". How do I go about getting a new tube from Bottlehead and returning the old one to you?