How to lower noise floor through mods?

IMO/IME its a Bad Idea to bypass coupling caps. The result is smearing. The more resolution your system has, the more you hear it. On low resolution systems it may sound like that cap got speeded up a little.

Your best shot is to put in the best coupling cap that you can.

If the power supply does not have the tube visible in plain sight, then its not there. A can over the tube would overheat it!

If you decide that you really want to tinker with this preamp yourself, **do yourself a huge favor**: go out and buy a kit from PAIA.com or bottlehead, build it up and make it work. It should look like it was built by an expert inside. Seriously, this is important because you can get in over your head very quickly modding things! There can be shock and fire hazards, both to yourself and others, plus in the real world probably only about 5% of the total modified units ever wind up being better than stock- in the other 95% the mod is a destructive act.

After you have built the kit, look into how it is built and see if you can mod that to do better. If not, don't attempt it on something that came ready-built! Above all though, this is supposed to fun. Don't loose sight of that either.

Atmasphere has it right, start modding with something less valuable. You build up your skills on the cheaper stuff, as you become more skilled you become more confident in working on the more valuable pieces. Read some basic electronics books and ask questions at some of the more technically based audio forums.

You shouldn't be scared to start modding, it can pay off in sonics that fullfill your needs. You just have to understand the hazzards of modifying, nothing is fullproof.

I'm not sure I agree with Atmasphere that only 5% of mods are better, up to now I would have to put my success rate at aprox. 75%, YMMV. Doing you're homework prior to diving in is critical. Also, some equipment is not amenable to modding, the manufacturer may have already used premium parts and/or the voicing may already be optimized. I suspect a coupling cap upgrade in your Jadis will give you what you're looking for.

Atmasphere and Sns, thanks much for the comments, and the warnings. In any case, I had already planned on doing a Bottlehead pre (then changing caps, then adding shunts), to see what it would sound like, before touching the Jadis. Part of it an education issue, part of it a safety issue.

Feet- Isopods , sorbothane, Vibrapods, LAT
Resisters- Vishay
Chassis damping- Soundcoat
Hexfreds
Electrolytics(power supply)- Blackgate, F&T, RDE
Coupling (output) caps-Mundorf gold, silver, ZN
Good tech to get proper direction on caps, optimize wiring scheme,etc.