Buzzing in right channel

[Rhydonia]

Hi All,

I recently completed a Crack build, and I'm having some problems with a constant buzzing sound in the right channel of my headphones. The noise is present at both low and high volumes, and does not seem to get any louder or quieter. Wiggling around the RCA jacks seems to change the tone of the noise somewhat, but nothing makes it go away.

My Crack passed all voltage, light, and visual checks as far as I can tell, so I'm not quite sure where to go from here. I did tighten down the 4 transformer screws and redid a few solders, but there was no change. Please let me know what additional information would be helpful in order to start troubleshooting. Thanks so much for the help!

[Paul Birkeland]

Posting photos of your build can be extremely helpful for troubleshooting an issue like this.

-PB

[Rhydonia]

Hmm, I'm hitting some sort of firewall when I try to upload images, and it seems external links aren't allowed, any suggestions?

[Paul Birkeland]

You can upload the images here on the forum, but the file size has a limitation, or you can just post plain text links in here.  We have had some enormous issues with embedded images from external hosts, so we disabled that functionality in the forum. 

[Rhydonia]

Ah, got it, thanks! Here's a plain text link: imgur.com/a/cg9JAVS

[Paul Birkeland]

The only thing that jumps out is that the resistor connection at 2U might not be all the way soldered.

In the absence of something obvious, I would try plugging an inexpensive pair of headphones into the Crack, then power it up and poke around each component with a wooden chopstick.  If you can change the noise by poking something, then you know what may be loose or causing issues.

-PB

[Rhydonia]

Hi Paul,

After some poking around, I believe the issue may lie with the 6080 tube. Placing the chopstick on or around the tube produced a vibrating feeling that seemed to line up with the frequency of the buzzing I'm hearing. Also, the 6080 tube seemed to get fairly hot after a few minutes of use.

Upon further inspection of the tube, is is possible it's not actually seated all the way? I can see a gap between the bottom of the tube and the socket, and the tube can't seat any further down because it's hitting on the 2 screws securing the socket. I attached a picture to try to clarify.

[Paul Birkeland]

If the 6080 doesn't get hot after a few minutes of use, that would be a problem.  The tube is fully seated, that isn't a problem.

Are you poking at the pins on the tube socket?  Which ones are causing the noise to come through?

If you are unable to activate the noise by poking around with a chopstick, you may need to let the amp run for a few days to cook in the cathodes.

[Rhydonia]

I am still unable to pin down the issue. In fact, the problem seems to be getting worse. Now the humming sound is in both channels, and it seems to get louder the longer the amp runs for. There is also now an issue where a loud sound similar to a record scratch or a zipper being pulled comes through for the first few seconds after I flip the power switch off. The 6080 tube does still seem kind of loose to me, as I can wiggle it around and that changes the humming sound. The other odd thing is that when I tip the amp up slightly or side to side, the sound changes. I must admit, I'm pretty stumped at this point...

[Paul Birkeland]

If wiggling the tube changes the sound, this very often means that there are loose components mounted to the socket, or one of the components mounted to the socket has a loose connection on its other end.

Looking at your pictures again, might the red wire at 7U be loose on the terminal strip?

I would also be sure the black wires at 3L are well connected, you may need to reheat that joint from the back side and slide them out slightly if the insulation is getting in the way.

[Rhydonia]

Nothing seemed loose at all, besides the pins themselves which have a bit of wiggle to them. I redid 7U and 3L just in case, but there was no change in either the buzzing noise or the weird sound when powering off. The only thing that changes the buzzing is tipping the entire assembly sideways instead of upright.

[Paul Birkeland]

It is possible that there is a funky contact in your 8 pin socket.  They are fork type receptacles where the tines of each fork can be nudged toward center with a small pick tool or a really tiny flat head screwdriver.

[Rhydonia]

I've fiddled around endlessly with the pins to no avail. The noise does change when I press a few of the loose pins into different positions, but they are too loose to stay in position once I try to adjust them. And even with the (temporary) adjustments I can get, the hum never goes away, only changes in tone. I've done more resoldering as well, which resulted in no change at all. I feel like there's definitely something funky with the tube/socket interface, but I can't think of anything else to try to fix it. There has also been no change in the strange static noise when powering off; do you have any thoughts on that?

[Paul Birkeland]

I got a Crack in today for repair that had this same symptom, and it turned out to be excessive soldering on one of the pot pins that allowed enough flux into the pot to cause continuity problems.

On your volume pot, on each level, you should be able to read 100K between the outer lugs.  With the pot all the way down, you should get about 0 ohms between the lugs with the black wires and each of the center lugs on the pot.  I would double check that you get these readings.  If one of the center lugs does not return a resistance reading (over limit), then you may have that same issue.

[Rhydonia]

All of those values seem to more or less check out - I got 100K spot on between the top 2 outer lugs, 86K between the bottom outer lugs, and 2 ohms between all of the black wire and center lugs.