What does a soundcard want to "see"....how can I get my tube preamp to provide it?

[the great wazoo]

I have a tube preamp putting out around 2.5V. Impedance is around 500K.
This is too hot for running direct but I am unsure what would be the best method to cool things off to make it suitable. A simple pot does not seem to be doing the trick, it kills the goods.
Anyone know what a soundcard wants to "see" and what I can put between it and the preamp to make things work right?
Simple is best... I think I could use a tube/transformer based DI type circuit but that is way more then I'd like to put into it... Aren't there some simple passive circuits that can change signal levels and impedance? .....sometime "T" or "I" comes to mind but I can't recall what they are called.
Any shoves in good directions are much appreciated!!
TIA!

[Enzo]

Well how did you wire that simple pot? A simple pot is exactly what I would use. Wire it up like any conventional volume control, then you can turn the output down from 2.5v to something lower.

[d95err]

Cheaper "consumer" soundcard line in typically accept -10dBv levels, while dedicated music gear often do +4dBv. Check the soundcard specifications to see what input levels it can handle.
More on line levels:
Line level - Wikipedia, the free encyclopedia

However, never push your soundcard anywhere near it's maximum input level, unless you really like digital clipping. If you record at 24bits, you can safely leave a 10dB margin and still have a signal-to-noise ratio way beyond what the most expensive analog gear can manage.

You probably need some way to get the output impedance of your preamp down. An audio transformer may be the most estetic solution in an all tube piece of equipment, with the added benefit of balanced output and ground lift. However, a simple solid state buffer at the output would also work. You could use a high-voltage MOSFET buffer (Google "MOSFET follies"), but a low voltage JFET buffer would work just as well if you take the signal level down to a decent level.

I would add a fixed voltage divider on the output of the current preamp to get the signal down to JFET safe levels, then the JFET buffer and then a low value volume pot (e.g. 10k).

[the great wazoo]

Thanks gents!!
I'll do some digging and study and post back what I might try working with.

[J M Fahey]

All above suggestions are excellent, yet just to get your feet wet and to curb the anxiety, make a voltage divider: a 470K 1/4W resistor in series with a 10K pot wired as a regular volume pot, into the Line in (forget the Mic in).
You will have 50mV there, way within spec.
I suspect that if you overdrive your tube preamp you will have much higher peaks, so I would wire two antiparallel silicon diodes across that volume pot, then you can never have more than 500mV there.
Good luck.