[Tyson]

I just set up my current speakers (GR Research V2's) to run fully active using a DCX as a crossover.  So, I have a custom VTA ST70 tube amp for the mids, and a 2nd identical amp for the highs, and some SS amps for the bass.

The problem is that I get hiss via my tweeters and it bothers me a bit.  It's definitely the amp, not my preamp or anything upstream.  I know this because have shorting plugs, so I used them to isolate the amp from the rest of the system.  Hiss is the same whether I have the amp plugged into the system, or if I am using the RCA shorting plugs.

I think part of the problem is my tweeters are very efficient, at 105db, and they are just picking up the noise floor of the amp. 

It is definitely HISS, and not HUM, so it's not a grounding problem.

Any thoughts on how I can get the hiss down to a lower level?

[mgalusha]

I'd pad the tweeter down to approximately the same level as the woofer. L-pad is probably the easiest way to go.

[Tyson]

Thanks Mike, I will give it a shot!

[Wind Chaser]

Or get an angry pet snake.  At least that way you could justify it.

[Niteshade]

You have a noisy gain stage. This can happen with a three tube setup. When the gain stages are not graduated properly, the amp will become susceptible to thermal noise and various other noise sources.

Being 105db sensitive doesn't help things at all! More than likely changing a few cathode resistors to higher values may help things out allot. If the cathode resistors in the voltage amp have capacitor bypasses, try removing them first.