Background noise + crackling/popping sound [Solved]

[Klots]

Hi! Finished my Crack yesterday and had a listen. There are few things that disturb me a little. I try to give as much information as I can.

When I finished soldering I did the resistance checks (every measurement was correct) and then voltage checks (also every measurment was correct). When I turn the amp on (with no DAC and laptop connected to it) and put my ear near the crack it hums and when I connect my headphones (HD700) in then the same hum comes through them. When I connect my laptop and dac (schiit modi) to it and turn on the music I hear crackling/popping. I removed all the electric stuff from near the Crack and that did not change anything. Both the hum and crackling/popping sound is in both channels. I re-heated all the joints 3 times and everything is still the same. The hum increases when I turn the volume from 0% to 100%. I add some pics also. If anyone sees anything problematic or have some ideas what to test or measure then please share your thoughts.

[Grainger49]

Crackling noise is often, but not always, a loose connection.  The chopstick method is a good way to go about it.  You flip the amp and poke at connections while listening.  Don't stop when you find one connection that makes a sound, go through all connections.

Hum is often impressed into the signal path by outside interferences.  Cell phones have caused pages of Crack posts.  Computers likewise.  If you got the computer 3' away from yours and there was no change I think you have eliminated the computer.

First try cleaning the tube socket/tube pins.  See the FAQ thread:

http://bottlehead.com/smf/index.php/topic,2408.0.html

It won't hurt to read the whole thread (what is left after the forum transition).

[Klots]

Crackling noise is often, but not always, a loose connection.  The chopstick method is a good way to go about it.  You flip the amp and poke at connections while listening.  Don't stop when you find one connection that makes a sound, go through all connections.

Hum is often impressed into the signal path by outside interferences.  Cell phones have caused pages of Crack posts.  Computers likewise.  If you got the computer 3' away from yours and there was no change I think you have eliminated the computer.

First try cleaning the tube socket/tube pins.  See the FAQ thread:

http://bottlehead.com/smf/index.php/topic,2408.0.html

It won't hurt to read the whole thread (what is left after the forum transition).

I was away from pc/mobile phone etc about 100ft  I cleaned tube sockets and pins. I try the chopstik method  Can an output tube make crackling sounds?

[Doc B.]

If the hum increases with the volume being turned up that means at least part of it is coming in from ahead of the volume control. That means either the cables or the source component is introducing it. This is one of those situations where I recommend shorting the input jacks to eliminate any influence of the source cables and components and also to avoid noise pickup from an open input jack. If the hum goes away you know that the problem isn't inside the Crack. Humming with crackling sounds to me like it could possibly be a bad shield connection inside a cable.

[Klots]

If the hum increases with the volume being turned up that means at least part of it is coming in from ahead of the volume control. That means either the cables or the source component is introducing it. This is one of those situations where I recommend shorting the input jacks to eliminate any influence of the source cables and components and also to avoid noise pickup from an open input jack. If the hum goes away you know that the problem isn't inside the Crack. Humming with crackling sounds to me like it could possibly be a bad shield connection inside a cable.

I did the chopstick method and all connections are solid. The cracking does happen mode often and a bit louder when the tube warms up (it depends on volume. Lower the volume the lower crackling there is). Maybe a stupid question but how do I shorten the input jacks?

I tested again that would the hum increase when I raise the volume and music was paused- When I listen to a song and pause, then the hum depends on volume. Lets say I pause and turn the volume to max, the hum goes louder. About 5 seconds and then the loud hum decreases to very silent. Basically after song is paused and about 5 seconds later I can turn volume min-max min-max, and it is almost silent. There is a hum when listening to music (easy to hear when silent parts in songs) and 5 seconds after the music stopped. And in that very silent hum there is a little sound like a mouse is eating through wood wall (very quietly). Maybe a stupid explanation, but that is how I hear it 

Otherwise I am very happy with the crack and the sound. It is a very good kit to build. Thanks for that! 

[galyons]

... how do I shorten the input jacks?

Make a simple RCA shorting plug by taking a short, cheap RCA interconnect. (The cheap ones that come with most audio/video devices) and simply cut off one plug leaving about 1/2" wire.  Remove the insulation from the wires.  Twist/crimp the ground wire to signal wire and you have your shorting plug. Need two, cut off another!!  Save the interconnect to make two more when you lose the first plugs!

You can get fancier, if you want.  Solder a 220-1K resistor between the ground and the signal, but really not necessary in this application.

I usually put a bit of shrink wrap on the exposed wires, on the cheap method, just for that final beauty touch! 

Cheers,
Geary

[Klots]

... how do I shorten the input jacks?

Make a simple RCA shorting plug by taking a short, cheap RCA interconnect. (The cheap ones that come with most audio/video devices) and simply cut off one plug leaving about 1/2" wire.  Remove the insulation from the wires.  Twist/crimp the ground wire to signal wire and you have your shorting plug. Need two, cut off another!!  Save the interconnect to make two more when you lose the first plugs!

You can get fancier, if you want.  Solder a 220-1K resistor between the ground and the signal, but really not necessary in this application.

I usually put a bit of shrink wrap on the exposed wires, on the cheap method, just for that final beauty touch! 

Cheers,
Geary

Thanks! Will try that tomorrow 

[Klots]

Doc, you mentioned bad shielding inside a cable. Any methods to test it? Can a output tube make that crackle/popping sound?

[Grainger49]

The shorting plugs test that the noise is completely inside your Crack.  That will clear your cables. 

If you use the shorting plugs and the noise goes away the way to clear your cables is to swap the cables coming in.

[Doc B.]

Yes a tube can make noise. That noise will not go up and down with the turning of the volume control in a Crack amp.

If a shield is bad in a cable that means it is probably not making contact inside the plug it is supposed to be connected to (some times just the plug at the source end, sometimes both ends). So you might find that the crackling happens if you wiggle the cable and that broken shield rubs the point where it should be fixed. Gringer's idea of eliminating this possibility by replacing the cables with know good ones to see if the noise stops is a good one.

[Klots]

I'm so sorry for being stupid  Fixed that noise. Just changed USB port and it is all OK. Yes tube hums a little but that is not a big thing. Gonna roll some tubes anyway soon. Thank you all for helping and now I can enjoy my crack even more