Dusting off the Rudistor RPX-33 mkII I bought used, a year ago.
Back then I tried it and was very disappointed. The Rudistor sounding bright and no lower midrange quality, nor bass. Incredible clarity, but flawed.
(The headphones were new at that time too. a pair of Sennheiser HD800s)
So it sat for nearly a year.
I finally pulled it out and plugged it back in, after using a tweak of pigtails on my main amp and gaining bass and mids. i made one for the ground portion of the headphone jack on the Rudistor.
WOW great, the full range of the music is there. Even without the pigtail, the Rudistor is better than it was a year ago. With the pigtail, the Rudistor and HD800 combo is really good.
I bought the Rudistor used, but it may have never been broken in? i do not know, but sitting for almost a year certainly it is better now. (or maybe the Sennheiser HD800s are fully broken in?) So much so i decided NOT to sell the Rudistor, and am selling a Little Dot MkIII i also have, and making the Rudistor my main headphone connection for certain.
i have to now decide if i want to sell my SinglePower headphone amp, another monster of a tube headphone amp.
I like it too, but the Rudistor is So great as it is now....

The interesting thing is the tonal quality of the Rudistor/HD800 is very similar (though of course different, too) as my systems Magnepan and bryston stuff