Power Filtering vs Power Regeneration?

Halcro,
Have you actually documented what's going on at the wall socket during those periods where the sound deteriorates? It would first be prudent to do that, so you are not wasting money on a (expensive) power regenerator. Another reason to do that is to determine the magnitude of the AC voltage swings, if indeed that is the cause of your problem. Because different regenerators will have different capacity to maintain constant AC output for a given variation in input AC. Two excellent brands of regenerator: PS Audio and Furman.

It's also possible that someone in your neighborhood who shares your AC or some household appliance is switching in and out, causing disturbance on your AC line, when switched in. In that case, of course, you need some sort of filter or dedicated AC lines, or both, and not necessarily a regenerator.

Halcro,
Look at this product:
http://www.orb-audio.jp/english/kyoto.htm

Quite a few have upgraded from really good power regenerators to this passive product in my city. I personally use the lower end model called 6GG and it is just terrific. Music is so pristine, detailed and extended, it is a revelation.

If you must use a regenerator then look at APS Purepower

I have been using the Silver Circle Audio pure power 5.0 unit for a while now and must say that it really does work very well--more retrieval of recorded ambience, quieter background, etc. The unit uses a massive transformer to isolate, so it's a passive unit--it also weighs around 100 pounds, so be careful lifting it. I initially was looking into the APS Purepower, but was scared off by the negative reports on the company and its customer support--check the APS Purepower thread right above this one. If going the regenerator route I would suggest the PS Audio units, they are backed by a reputable company and from reports work quite well.

Lewm,
I don't know what goes on at the wall socket and have no instruments to test it...😱
I've had the Shindo Mr T passive transformer-based power conditioner for the past two years and can report that it does nothing for my sound quality nor for the monthly deterioration in sound quality....😩
I am assuming from this...that it may be a voltage spike so large that it affects the power supply of the Halcro preamp/phonostage. The sound quality is normally then affected for up to three days before settling down...😖
I installed the PS Audio P3 power regenerator yesterday and whilst I need to wait at least 3 months to see if it cures the problem.....I can report that there is a significant improvement in the resolution, noise-floor, bass extension and treble smoothness...and I mean 'significant'...😘
What the P3 also tells me is that the voltage from the wall outlet is a pretty steady 250 volts (Australia has a nominal 240V supply) and I have elected to output a steady sinewave from the P3 of 235V at present..👀
I will monitor the situation closely for the next 3 months but this is the first power conditioning item I've used to really audibly affect the sound quality for the better.....👍

Pani, A passive device simply cannot solve Halcro's problem, if the problem has to do with AC power sags or surges. End of story.

Halcro, If you search on eBay you may find an inexpensive chart recorder that can be used to monitor AC at the wall socket vs time. What is the wattage rating of the P3? Can it handle your amplifiers' peak needs? That's the big issue with using a power regenerator to supply an amplifier. Otherwise, good choice.
I use a PS Audio 300 (300W) to supply the front end of my basement Beveridge-based system. After 10 minutes, I would not live without it, just for its cleansing effect on the music. (I of course do not use it to power the Beveridge direct-drive amplifiers; they just plug directly into the wall.)