New build hum

[hokenpoke]

I finished up the Crack last night and did resistance and voltage checks - all good.  I fired it up with audio today and it makes good sound but with an underlying hum. 60hz, of course, doesn't vary with the volume, present with or without source attached and dies as soon as power is cut.

Is the heater string perhaps jumping onto the output.  I will attempt to add pics in following posts - board has not let me so far.

[hokenpoke]

Pic 1

[hokenpoke]

Pic 2

[hokenpoke]

Pic 3

[Mucker]

Photo management is a bit tricky at first. If you want to delete a photo, just uncheck it and save the post and then go back to modify. Then it will disappear. You can add multiple photos to one post too.

As far as hum, did you let the tube burn for a few hours?

[hokenpoke]

Thanks for the tips on photos.

I have not let the tube burn. Will that make a significant difference in hum?

[Mucker]

It could but you may have another issue as well.

[Doc B.]

What headphones are you using? Is the hum soft or buzzy?

[hokenpoke]

I'm using Sennheiser HD-6XX.  The hum is soft in tone but at a reasonable volume level - it will disappear under moderate level music.

[Paul Birkeland]

12 and 14 should be connected with a black wire, I don't see yours???

Hopefully the stranded wire you used wasn't provided by us.  I would strongly suggest removing it and putting in what we provided if possible.

[hokenpoke]

12 and 14 are tied together - just hidden under the filter caps.

I replaced the heater string between the rectifier with solid core and flew it up and away from the rest of the signal path. After this the buzz got worse so I poked around with a chopstick and found the problem - an incomplete solder joint on the output jack sleeve terminal.

Now there is no resting state hum when the tubes are not warmed up.  When the tubes come up, there is a quiet hum which does vary with the volume pot. I assume this is from the heater string so I will see if there is an configuration that cuts this down some.

[Paul Birkeland]

If you have nothing plugged into the RCA jacks, then you will get some noise that varies with the position of the volume control.

[Doc B.]

Making the twisted pair heater wiring lay close to the chassis panel (ground plane) is the best setup to minimize radiated electrical field from the twisted pair. Hum that varies with the volume knob position is not coming from the heaters, it is coming from the input, ahead of the volume control.