Reading about the NuPrime ST-10 recently made me curious to ask about it here. I have been enjoying the NuForce HAP-100 and STA-100 combination for just about a year. Their engineering prowess has won my full respect. So, I knew the ST-10 had to be something worth looking into. After asking about the ST-10 here, Mark Sossa, of Well Pleased AV, Alexandria, VA was kind enough to offer to send me a loaner to evaluate.
The differences I heard were both immediate, and subtle.
The ST-10's bottom-end heft
brought back memories of a powerful tube amp. I once owned a refurbished Mac MC 275. KT88's. Yet, unlike the 275, the ST-10's bass is tighter and well controlled. The heft was there. But, its a heft that a powerful tube amp can not match when it comes to control. There was also an over all warmth to the sound that again reminded me of tubes. But, I was also hearing along with that warmth details with a silent background. One that gives what I call a noiseless clarity. I have never heard such clarity and silence together with any tubes I heard before. Not that I heard a great many tube amps.. so to be fair. Keep that in mind.
Mid-range: Both the ST-10 and the NuForce STA-100 share this common family trait. Its their mid range. Which is a great place to be. But, the ST-10 hugs its mid-range with a weightier sounding foundation.
The high end: The high end of the ST-10 has a sweetness that the STA-100 will not match. That is not to say that the STA-100 is harsh in its high-end. It is not. It just does not convey that kind of sweetness that the ST-10 can. What I heard on certain recordings while listening to the ST-10 was a nice relaxing shimmer to cymbals.
I play drums. Cymbals (and drums) will sound different from room to room. There are bad rooms.. good rooms.. and, there are excellent rooms. Its only in the excellent rooms that cymbals will sound like I heard with the ST-10. Again, its not to knock the STA-100. For, the STA-100 has also a believably realistic high-end. But places you in a different kind of room. One not as sweet with that excellent room type cymbal shimmer.
I only have the NuForce STA-100 to compare directly with at this time. I found the ST-10 is more relaxing to listen to. In contrast, the STA-100 has a tendency to make you sit up and take notice. Both good in their own right. But, not the same. IMHO, I would recommend the ST-10 for someone with a room filling system. One who likes listening to large-as-life imaging. At present.. I listen desktop, near-field, these days. I soon found out that the ST-10 is a bit of overkill for my needs. Just the same. Its true. Its a great amp! ...
Addendum: Since then I have begun enjoying the benefits of using balanced connections. In a DESKTOP setting the ST-10 can shine as shown by Steven Stone in his ST-10 review. http://www.theabsolutesound.com/articles/nuprime-dac-10h-dacpre-and-st-10-power-amplifier/?page=4