"As someone who has been plagued by headphone amps with annoyingly touchy volume controls, I embraced the addition of a gain control to the RP5.1. Normally the amount of movement it takes to adjust the volume is far too little, so the volume jumps with only the slightest amount of movement, making it difficult or impossible to find the right setting. With the RP5.1 you can adjust the gain to compensate for several factors: headphone sensitivity, volume-control sensitivity, CD-player output, background noise, and the sensitivity of your ears. Without gain control you’re often near the lowest setting of the volume potentiometer, which nine times out of ten means you have a channel imbalance, which can be very noticeable with headphones. With the RP5.1, I found that if I simply reduced the gain of the amp to the point where the volume control is at about the 12:00 position, I’ve solved all of the potential issues I mentioned in one shot. I was left with plenty of gain and a less-sensitive volume control that allows for small adjustments, and I eliminated any chance of channel imbalance. "
"One of the rather amazing traits of the RP5.1 is just how lively its sound is. Headphone amps, especially tubed headphone amps, can sometimes sound rather slow, sluggish and boring. This is the antithesis of how the hybrid RP5.1 sounds. Listening session after listening session with the RP5.1 impressed me with how much enjoyment its lively and fast character brought. Terry Talbot’s guitar work on his and Barry McGuire’s album When Dinosaurs Walked the Earth [Sparrow TM-1001] had crispness and snap, and this created a realistic illusion that he was in the room playing. Again, each pluck of the strings sounded right, which is no mean feat at all. Many a headphone amp has failed to reproduce these notes with the proper amount of snap and attack, setting the RudiStor RP5.1 apart right away."
"To say that I was impressed with the RudiStor RP5.1 would be a rather large understatement. It arrived with neither fanfare nor pomp, but left a lasting impression on me that far exceeded what I expected. It is the liveliest, most enjoyable headphone amp I’ve heard at anywhere near its asking price. If I had to choose a single headphone amp for under $1500, I would, without hesitation or reservation, choose the RudiStor RP5.1."