Loud hum when volume is at 0%

[lokesen]

I have build a Bottlehead Crack with Speedball upgrade I just build.

My problem is it has a very loud hum in both channels, but only at 0% volume and it disappears after 10 minutes of so playing music.

I have checked all soldering and reheated them all. It has stock tubes. All voltages show about 8-10 volt lower than manual states.

[Paul Birkeland]

My problem is it has a very loud hum in both channels, but only at 0% volume and it disappears after 10 minutes of so playing music.

So the problem is present for 10 minutes, then goes away?

The first thing I would try is tightening the #8 screw by the IEC inlet.

[lokesen]

My problem is it has a very loud hum in both channels, but only at 0% volume and it disappears after 10 minutes of so playing music.

So the problem is present for 10 minutes, then goes away?

The first thing I would try is tightening the #8 screw by the IEC inlet.

Not a bad idea!

I just tightened it quite a bit. I waiting for the amp to get cold again to test it

EDIT: No - didn't help. Could it be a faulty tube?

[lokesen]

    .  .  .    very loud hum in both channels, but only at 0% volume    .    .    .    .     

You say "only at 0% volume.  So, if you bring the volume control to 1/4 or 1/2 how is it?  Since you also say you play music and it goes away it kind of indicated that there is hum after you come off 0 on the volume control.

If it is worst when you are at 0 volume I suspect your ground on the volume control is not solidly connected.

Look in the Crack folder for the sticky that traces the ground circuit and verify the ground for the volume control.  Then post back.

Good luck!

It's only a 0%. Disappears completely above 0.0%. 

[Doc B.]

This probably means that either the wiper in the pot is lifting at the bottom end of its travel or there is an intermittent connection to one of the ground lugs of the pot.

[serpent68]

I have the same problem when using the E80CC tube with the TS 5998 tube.  The loud hum / buzz is only there when volume is at 0%, goes away immediately when I turn the volume up.  No such symptom when I run a regular 12AU7 tube with the TS 5998, or when I use the E80CC with the 6080, or when I use the stock tubes.

I have a 100k Valab step pot.  Beyond the 0% volume, the music sounds wonderful without any hint of noise.

Strange problem that I could not figure out.  Maybe certain condition invoke a faulty ground connection?

[Paul Joppa]

Lack of grid stopper?  :^)

[lokesen]

This probably means that either the wiper in the pot is lifting at the bottom end of its travel or there is an intermittent connection to one of the ground lugs of the pot.

I think you're right about the location of the problem. I'll try to resolder or change the pot.

[JamieMcC]

I have the same problem when using the E80CC tube with the TS 5998 tube.  The loud hum / buzz is only there when volume is at 0%, goes away immediately when I turn the volume up.  No such symptom when I run a regular 12AU7 tube with the TS 5998, or when I use the E80CC with the 6080, or when I use the stock tubes.

I have a 100k Valab step pot.  Beyond the 0% volume, the music sounds wonderful without any hint of noise.

Lack of grid stopper?  :^)

I had to look up Grid Stopper (thanks PJ my education continues) I often run the same configuration with the Valab fitted, I do get some noise as described above which is not present when running the 12au7.

however mine is more intermittent and seems be also dac and source dependent.

If I stream from pc to dac I have very slight noise ie the background is not black, when playing music this can not be heard.

If I listen to internet radio (dac feature) No noise same internet connection just different output source selected on dac.

If I connect pc via usb then no noise.

So could this be the frequency/oscillation aspect I see in mentioned in conjunction with the grid stopper?

What might the oscillation sound like? a very fast flickering?

I have been just changing my input to avoid this noise and was going to see if streaming via optical connection to my dac helped next.  If the gird stopper might be a option it is something else to try.

Jamie

 

[krystalnx]

Hi,

got almost the same issue on my "brand new" crack + speedball.

Waiting for ebay parts to confirm it's a tube issue

http://bottlehead.com/smf/index.php/topic,5756.0.html

[Paul Birkeland]

however mine is more intermittent and seems be also dac and source dependent.

If I stream from pc to dac I have very slight noise ie the background is not black, when playing music this can not be heard.

If I listen to internet radio (dac feature) No noise same internet connection just different output source selected on dac.

If I connect pc via usb then no noise.

So could this be the frequency/oscillation aspect I see in mentioned in conjunction with the grid stopper?

What might the oscillation sound like? a very fast flickering?

I have been just changing my input to avoid this noise and was going to see if streaming via optical connection to my dac helped next.  If the gird stopper might be a option it is something else to try.

This sounds a lot like a floating ground at the input.  A USB cable connected to a computer that's plugged into the wall (not a laptop), will give you a good connection to ground.  If this floats, I'd recommend buying some coax interconnects. (We have found that these are incredibly quiet from such a source)

[JamieMcC]

Thanks Paul for your input re floating ground, learning something new again! I have since had a bit of a sort out and have relocated my server and now have the dac hardwired to source which in turn can be wifi controlled and am having no issues. As all is groovy I will leave well enough alone for the time being.

[lokesen]

I have solved the problem. I bought a new power tube and problem was gone immediately. So it turns out the RCA tube that came with the crack was defective from the very beginning. I'll try to get a replacement. Cheers guys and thank for your advise (although they didn't solve the problem)