Crack Hum [resolved]

[niall lindsay]

Just completed Crack build and I have a background hum issue - it is not too loud but you can hear it on quiet passages of music. I have read a lot of the posts offering solutions which I have tried. The only non standard component I used was swapping out the potentiomentmeter with a Blue Alps which is working perfectly. The hum is not affected by the volume control. I have checked the earthing lines and the power capacitor connections and the soldered joints look ok. Ditto the socket connections on the main large tube socket. Not sure where I go from here or what to do next. :-\

 

[Paul Birkeland]

Is it hum or buzz?  Depending on where you live, hum will be 50Hz or 60Hz and buzz will be 100Hz or 120Hz.  You can listen to these tones with a tone generator app or with YouTube.

Can you post some photos of your build?

 

[niall lindsay]

Just checked the wiring again. I have a slightly different wiring route for one of the power lines in that the wire that connects to A4 and A5 goes around the outside and under terminal strip 1 to 6 rather than follow the inside line of the terminal strip as indicated in the diagram but I wouldn't have thought that would have made a material difference. Thoughts.

Also is anyone able to confirm the full grounding route so I can check triple check the grounding.

Although the background hum isn't a major deal it can be hear on quiet passages of music and from posts on the forum I understand the crack should be totally silent.

All of the resistance checks and voltage checks are compliant.

Any guidance much appreciated.

 

[niall lindsay]

Paul

I would describe is as a HUM. I am in the UK so working of 240 volts. I will take some pictures of the build as you suggest

N

 

[niall lindsay]

Paul

Some photos attatched as requested.

N

 

[niall lindsay]

Paul

It is a 50-60Hz Hum which I guess is an earthing issue but I cannot for the life of me trace it.

N

 

[Paul Birkeland]

The routing of the green wires up at the 9 pin socket could indeed be a big part of the issue.

Notice that you have the wire going to A9 running in parallel with the wire going to A7?  That could induce some hum.  In the stock layout, the green wire is a bit shorter and it take a more direct route that's not in parallel with the signal carrying wire going to A7.  Having said that, however, noise induced in that matter should be influenced a bit by the volume pot, especially if it's all the way down.

Similarly the wiring going to A4/A5 could be causing similar problems.  These are difficult recommendations because even tidying these up, the hum may not change.

Are the power outlets you're using properly earthed?  Is the noise present with no source connected?

 

[niall lindsay]

Paul

Thanks for getting back to me so quickly. Yes the hum exists with no source plugged into the RCAs. Should l re-route the wire that is located on  the outside of the terminal strip to the other side as shown in the manual and also  try and create some physical seperation between A4/5?. The volume control plays no part in the hum it is just a constant presence and its volume does not rise or diminish with the volume control.

Sorry if this is a dumb question but which power outlets are you referring to - the ring main socket?

Best

N

 

[Deke609]

You might also test whether moving the rca-to-pot signal wiring away from the transformer and diodes makes any difference. Maybe try moving the braided black/red/white wires about a 1/2 inch farther away. Worth a shot.

cheers, Derek

 

[niall lindsay]

Derek

Good suggestion. I will try it.

Thanks

N

 

[niall lindsay]

Paul

I will reroute the green power line to the 9 pin socket (A4/5 & 9) to create greater physical seperation with the other wires and see if that makes a difference.

I really appreciate your advice on this.

Other than the slight background hum the quality of the sound through the Crack is astonishing.

N

 

[Paul Birkeland]

I would just make it look as much like what's in the manual as possible.

 

[niall lindsay]

Paul

You were absolutley right it was the parallell proximity of the wiring to A77A9 that was creating the induced Hum. Now totally silent.

Many thanks for your help and support

N

 

[Paul Birkeland]

I'm actually very appreciative that you came back to let me know.  It's one thing to say that the layout is important, but it's something else all together to see that experience play out.

-PB

 

[niall lindsay]

Pleasure. If it helps any other Bottlehead fans in future then that is a big plus.

Best

Niall