My speedball is humming

[moviedave]

So, my readings all check out.  I have sound out of both channels, but I have a humming in the background on both channels that doesn't go away.  It isn't affected by cranking the volume pot up or down.  I figured it was a grounding problem, and since it wasn't there with the stock kit, went about trying to find a bad joint amongst my grounds.  I was unable to find any, however.  I even gave it the chop stick test, but was unable to make that hum go away.  Any thoughts out there?

[Lar]

Problem tube?

[moviedave]

No, unfortunately

[Paul Birkeland]

I'm going to assume that the kit is still stock (though mods that work to the kit w/o Speedball should work just fine with the Speedball).

Since you have swapped tubes, there are other things to try.

1.  Move the Crack to a different room or building.  Sometimes environmental noise creeps in.

2.  Measure the AC voltage between the chassis plate and terminals 1 and 5.  This will tell us how much noise is coming out of the driver stage.

3.  Measure the AC voltage between the chassis plate and the tip and ring of the headphone jack (assuming you don't have the shorting mod stickied in this forum)

Those numbers and experiments should be helpful.

[moviedave]

I am having trouble getting consistent AC readings.  All it seems to be picking up on is current in the air.  And no dice moving it to another room.

[Doc B.]

Is the hum buzzy, or soft sounding?

[moviedave]

more buzzy

[Doc B.]

That's a bad ground connection.

[moviedave]

I can't find the issue to save my life.  I resoldered 3U and the grounds on the speedball, but no luck.  I keep poking around with my multimeter with a cheap pair of headphones on, trying to see if I can find something that will affect the hum, but I just can't find anything.  It is frustrating the dickens out of me

[Paul Birkeland]

120Hz buzz would be a loose #8 screw back at the IEC inlet, a loose screw mounting the front transformer screw, or a loose transformer screw.

[Doc B.]

Try disconnectig your source and see if the hum goes away. It mght be a ground loop between the Crack and the source component.

[moviedave]

The hum is still there with the source disconnected and the RCA inputs shorted.

[Doc B.]

Is the buzz audible the instant you turn on the power, or does it come on later as the tubes warm up?

[moviedave]

It takes about... 15 seconds or so before the humming starts.