Crack ticking only when volume down

[bboris77]

Hi everyone, I built my first Crack a few days ago. I got the speedball upgrade with it. The amp sounds AMAZING. I have one small issue that has got me puzzled. Basically, the amp makes a very soft and repetitive click (similar to a watch). It appears each 5 seconds. It goes from the right to the left channel and changes in intensity. It appears with and without RCAs connected. However, and  this is where it gets bizzare, it only happens when the volume pot is tuned all the way down. I have triple-checked everything, resoldered all the iffy connections, cleaned the tubes, ruled out wifi routers, cellphones and tried different tubes. It is not a big deal at all since the clicking stops as soon as I turn up the volume, but I am just wondering if there is a logical explanation of why this may be happening.

Another thing is that the volume pot is very sensitive and I cannot get it higher than 11 o'clock on my HD600 without hurting my hearing. Is it normal that the amp is this loud?

Thank you in advance for any suggestions and I would appreciate it if someone could check if their crack with speedball does a similar thing with volume all the way down.

[bboris77]

I forgot to mention, all my voltages and resistance checks were spot on. And a further update - when the volume knob is all the way down, the ticking is the loudest and it is right in the middle of the soundstage. When I increase the volume to 1/4 of the full volume the ticking is much more quiet and is situated in the left channel. When I increase it to the full volume, the noise is again louder and located exactly in the middle.  These clicks are spaced exactly 5 seconds apart.

Here is the voodoo part - if I put my hand in front of the preamp tube without actually touching it, the noise goes away!  These clicks are spaced exactly 5 seconds apart. I still have not tried to take the amp to a different house to see if it is some radio interference. Any suggestions would be appreciated.

[fullheadofnothing]

Any suggestions would be appreciated.

I still have not tried to take the amp to a different house to see if it is some radio interference.

[Paul Birkeland]

Try setting your phone to airplane mode.

[bboris77]

Try setting your phone to airplane mode.

Thank you for this suggestion. This was one of the first things I did and had no effect on the situation. Could this be an issue with the volume potentiometer? The reason why I am suggesting this is because the ticking noise changes in intensity depending on whether the volume pot is turned all the way to the left, or left at some point in the middle. This is 100% repeatable. It is definitely the most noticeable in the "volume off" position. Assuming this is some kind of RFI or even powerline interference, do you guys know why turning down the volume pot to zero would make the ticking become prominent?

I will try two things over the weekend:
1. Take the amp to my parent's house and see how it behaves there.
2. Turn off all the breakers in my house, except one, and try plugging it in that outlet.

[Paul Birkeland]

Are you feeding your Crack with signal from a computer?  Sometimes there can be strange interference noises generated when using a computer as a source. 

If you're using your phone as a source, try it on airplane mode, then also try it playing back from memory. 

As always, issues like this can often be flaky solder joints in the amplifier which are disturbed when installing the Speedball.

[bboris77]

Are you feeding your Crack with signal from a computer?  Sometimes there can be strange interference noises generated when using a computer as a source. 

If you're using your phone as a source, try it on airplane mode, then also try it playing back from memory. 

As always, issues like this can often be flaky solder joints in the amplifier which are disturbed when installing the Speedball.

It is being fed by Schiit Modi 2U, but the noise is present with no inputs attached as well. I have retouched all the joints as well. However, it is the regular nature of this tapping/ticking noise (every 5 seconds) as well as the fact that it stops if I shield the input tube and potentiometer area with my hand that it is some form of interference. It is one of those things that drive you crazy once you hear them. I will get down to the bottom of it though.

[kgoss]

Is the amp close to a wireless router or maybe a Bluetooth device?  Try moving it around in your house.  Try turning off routers, Bluetooth devices, etc one at a time while listening.  Heck, turn off every electronic device one at a time including your computer.  Once the interfering device is known you can start playing around with placement to minimize or eliminate the interference.

[bboris77]

Ok here is an update. I took the amp to my parent's house that is a few block away from where we live. On the second floor of their house the amp exhibited exactly the same noise. I then tried it on the first floor and basement - no noise whatsoever! Then I went back to my house and tried it in our basement and the amp was dead silent. That would explain why I never noticed any noise when I was putting it together in my basement.

Our neighborhood is relatively close to the airport (2-3 Km) so I can only assume this is some kind of radar or radio ping from a very powerful transmitter. That would explain why the crack is only picking it up on the second floor and not lower. I wonder if there is anything I can do to insulate it better to reject this kind of interference. For now, I have positioned the amp at an angle in which the interference is borderline inaudible but I would prefer a more elegant solution. Does any know which part exactly is it within the amp that is the most sensitive to RFI? Thanks in advance.

[Doc B.]

You could get a tube shield and bayonet base and install them over the 12AU7 socket. It will be kind of a PITA to do on a built amp. An alternative is to wrap the tube in copper foil, solder a wire to the foil and attach the wire to the chassis.

[Chris65]

You can also find the Military style slip-over tube shields made by IERC & others. Saves having to change out the socket.

[Doc B.]

Won't do any good unless the shield is grounded to the chassis.

[Deluk]

I like your idea as to the radar/radio ping but unless the piece of kit has only been commissioned in the last few days I'm sure that the interference would have been noticed locally before, especially at closer proximity to the airport. Police and taxi driver radios would have been very prone to picking it up, I would have thought. However, some communication radios do bleep at intervals just to keep you reminded that they are still working.
Off the wall, but do the rooms, yours and parents, that give the ping have fluorescent lights? I'm thinking a regular clicking starter. Did you take your phone to your parents?

[Chris65]

Won't do any good unless the shield is grounded to the chassis.

Exactly, was thinking a wire soldered to the shield & attached to the chassis (as you mentioned for the copper foil trick).

[bboris77]

I like your idea as to the radar/radio ping but unless the piece of kit has only been commissioned in the last few days I'm sure that the interference would have been noticed locally before, especially at closer proximity to the airport. Police and taxi driver radios would have been very prone to picking it up, I would have thought. However, some communication radios do bleep at intervals just to keep you reminded that they are still working.
Off the wall, but do the rooms, yours and parents, that give the ping have fluorescent lights? I'm thinking a regular clicking starter. Did you take your phone to your parents?

All the rooms in our neighborhood are energy-friendly, so they all have fluorescent light bulbs. I assume that they only interfere when they are on, right? Anyway, the basements have those lights too, and the amp is dead silent in the basement. My phone is always off when I test these things