I'm in the process of registering on Bottlehead's site for the forum, but meanwhile, thought I'd pose the question here.
I have a low level audible hum on my Crack, in both channels, and it doesn't vary with the volume knob. When I tap the side of the chassis, sometimes I can get it to go away, but most of the time it's there. When I turn off the Crack using on/off switch, I hear some static and a semi-loud pop before it finally powers off. I tried different tubes, so it's not the tubes.
Anyone have any ideas? Can a cold solder joint can cause a hum like this? Since it's on both channels and not dependent upon volume control, can I conclude it's somewhere early in the signal/power chain?
I just upgraded to Speedball tonight. The hum was there before the upgrade, I was semi-hoping that the upgrade might cure the hum, but not so lucky.
I have to admit. . .and maybe this is where I start. I never did voltage checks after the original build or upgrade. I figured the whole thing was powered up already, the tubes were on, and I'd take a chance by plugging in a cheap pair of headphones and just seeing whether I get music rather than risk shocking myself silly.
But maybe I'll have to do some voltage probing after all. One thing I couldn't figure out how everyone else handles: When your tubes are in and you're probing voltages, do you prop up the amp at an angle so you have access to the underside without having the amp sitting tube side down? Or have it sit upside down in the chassis and route the power cord from below?
Thanks for any help - I know this is technical support, but since this is a DIY and this is really bugging me (and while I'm waiting for my request to be approved on Bottlehead's forum), I'm hoping for some thoughts/suggestions in the meanwhile.
