Thinking about buying a different tube preamp...

Abuck,
Something seems very wrong here.

1) Good tube preamps (including the Modwright) don't normally making loud hiss

2) In many years in this hobby you're the first I've heard of inserting a PVC preamp between an active preamp and amp to try to eliminate noise. An extra box and extra cables should be helping.

Perhaps there's an impedance mismatch? what are the specs on the amp and pre in that regard. Maybe someone more technical than me can comment based on that additional info.
Don't give up, figure it out :-) Cheers,
Spencer

Talked with Dan at Modwright and he said some of the earlier models had a bit of tube rush.
The LS-100 has an output impedance of 300 ohms. The Classe monoblocks have an input impedance of 75K ohms. As far as using the pvc I'm happy with it. Just an added resistance between the components that doesn't add any unique traits of it's own.
When I had the Jolida Music Envoy in the system I had to attenuate the signal with the pvc because the signal was popping, causing the speaker drivers to extend to full excursion. Luckily nothing was damaged. Originally I didn't insert the pvc in this set-up, but when looking the system over, I glanced at the pvc sitting there and wondered...wouldn't hurt to try it back in the same configuration to see what would happen. Surprised me when it reduced the noise floor considerably.

I am surprised no one mentioned CAT SL-1, perhaps the most famous and long lived preamp with built in phono. It is also one of the few that can drive any SS amp due to it's 100 ohm output impedance. The latest and greatest incarnation is called Renaissance.

Dealer disclosure

Kyomi_audio, I did look at one that is still listed for sale on this site. It was a serious contender, but I don't remember why I didn't choose it. Looked at many.

FWIW it sounds like the amp has too much gain.

You should not have to insert a passive control to set things right- and don't think for a minute that passive controls don't have an effect! If you can eliminate it you will get more immediacy and more impact.

We use tube preamps on speakers that have a good 12 db more efficiency than yours with no problems. So its my opinion that you have a matching problem or a noise problem at the input of the amp.

Did the Jolida have noise without the passive??