Quote:   I'm thinking of upgrading to the long plates too, but I don't really know the differences I should be expecting.  I picked up these short plates Mullards for $9.50 shipped on ebay since my only intention was to solve the hissing problem.  My HD650s are also fairly new, so I...

And I'm already ready to upgrade. Haha. 

I found the problem that caused the hiss.  I replaced the 6080 with a RCA 6AS7G, no luck.  Swapped the EH 12AU7 with another one (Mullard) and the hiss instantly went away.  Now I can't seem to take my headphones off. 

It's a hiss, like white noise.  I read on the Bottlehead forum that it can happen with some tubes, especially if the tubes are fairly new.  I ordered some 6AS7G to replace the 6080.  If that helps, great.  If not, we'll see.   

Thanks.  I tried that. No luck.  I tried cleaning the pins on the output tube a bit, no luck there either.  Get new tubes? Haha.    This is my first tube amp, so I'm not completely familiar with how it works.  After powering on, the the left channels comes through first after a few seconds...

I just received a used Crack with the Speedball upgrade.  I have some background noise coming through the left channel even with the volume turned down and inputs disconnected. The right channel is silent.  Is this normal?  Thanks.

I actually just picked up a used factory assembled Crack w/ Speedball from the FS here.  My setup will be Matrix Mini-i --> Crack ---> HD650. I just bought the HD650 as well and it'll show up separately with the amp next week.  I have to say I'm pretty excited.  I kind of wished I had built the...