How to lower noise floor through mods?

T_bone, if you have an older piece that you are wanting to update, the first thing to do is make sure that its actually working right first. To that end replacing the filter caps is the most important thing to do. You can get a lot of the aluminum can style caps from tubesandmore.com

Its not likely that improved resistors will be a whole lot quieter, but they will sound better. If you change coupling caps, which is where you will hear the most improvement, its a good idea to keep the following in mind: You can get better bass with larger caps, but you will pay a price in transparency and if the RC time constant associated with the cap is lower than that of the power supply low frequency pole, you will do your self a disservice. So I would stick with stock values for the most part.

Going to HEXFREDs is a nice touch although tube rectifiers are often lower noise. However, the higher output voltage that you get from semiconductors might allow you to install a high voltage regulation scheme. If you can do that, you will be instantly rewarded as long as the result is a B+ that is at least as high as stock! There used to be a device called the VB408 that was a high voltage regulator, very nicely suited for tube work. If you regulate, thats where you get the nice low noise floor.

Don't make a rat's nest of the insides. Keep your layout neat, with minimal wiring. It is a good idea to use a star-grounding technique and avoid using the chassis as ground. Its not OK even if the original manufacturer did it. That will help you get low noise too.

Have fun!!

Thanks to all so far for responding.

Sns, it indeed is the Jadis I am thinking of working on. I am not nearly as comfortable with DIY as I would like to be.

Atmasphere, thanks for chiming in. The pre is a Jadis JP80, and it sounds wonderful as is, but I can hear where it is a bit off the mark vs other things I have had in my systems so want to try that. Without having schematics, I am a bit worried about going in myself (actually, with schematics, I am a bit worried about going in myself), but in this thread I am trying to learn which approaches will get me what I want. The pre has a separate power supply, which is beefy, and I have never felt it to be lacking. I think it is perhaps the main strength of the pre. I do not know how it is regulated. The newer versions are tube-rectified. At some point in the past, the power supply was SS. According to Arthur Salvatore's website, that started in 1990 and lasted a few years. Mine is a single-digit serial number, which would suggest it was before Jadis went SS, but since the aluminum cylinders in the back of the PS have covered tops, and I have not looked under the deck, I do not know if they are caps or completely enclosed tubes (and I am too much of a circuitry innards neophyte to have any confidence about what I see other than transformers, glowing tubes, resistors, and clearly marked caps (and, of course, I can usually tell what wire is)). Are "filter caps" the output coupling caps? And last question, would you suggest using a small cap in parallel as a shunt cap, as some do?

The "filter caps" are in the power supply. If you can still find Black Gate/Rubycon caps in the exact value that you've got in your pre now: They'd be a much higher performance replacement than the originals. I absolutely agree with Atmasphere- If your pre has tube rectification: Ignore my suggestion to go to FREDs.

I've investigated replacing the electrolytics in my Cayin power supply with a better electrolytic. Problem is the Black Gates/Rubycons are too low voltage rating (at least I've not found a source for higher voltage) for use in power supplies. I suspect he probably has decent electrolytics in his power supply, likely some better model of Nichicon, bypassing/shunt with film caps may be his best bet. I'm going this route in my power supply.

I believe coupling caps are the biggest bang for the buck, sonically speaking, these should be somewhere near the signal tubes. Not a job for the novice, find an experienced tech.

Have you thought of adding a power conditioner to your system? This made a big difference in my system.