my kit is generating hiss through both outputs regardless of the setting of gain or trim controls. The gain and trim knobs could be set completely counterclockwise and the hiss remains.
If the gain and volume controls are all set counterclockwise, and you still hear hiss... then the hiss is not coming from the preamp.
This is a typical example of the amount of hiss you should hear.http://www.fivefishstudios.com/audio/kol/Silence.mp3
Gain=48dB, max volume (max. Clockwise), attached to 15ft of cable, laying on the floor, surrounded by AC wires, etc...
It passes signal just fine, but the hiss is present the moment the device is turned on. It is constant and unaffected by the type of microphone or the use of phantom power.
As I said, the hiss doesn't seem to be caused by the preamp electronics.
I would look more into grounding, etc... case grounded, wiring, cabling, etc. ... or maybe even to the device where this is connected to.
What kind of housing/case are you using? Is your case properly grounded? (But even then, an improperly grounded case will be more of a humming noise and just bunch of RF junk... not hiss.)
I'm assuming you're connecting the balanced outputs of the preamps to some balanced inputs?
is that the LED2 spot on the PSU had 18 volts running across it for some reason (which makes a short a suspect).
If there's a short, you'd see 0 volts. But I don't see this related to your hiss problem.
The spot for LED2 is connected to one of the 18V outputs with a series limiting resistor. So yes, you'd measure 18V across it.