Rowland Concentra vs. Concentra II

Concentra is 100watts channel into 8ohms.
Concentra II is 150watts Channel into 8ohms.

I've only listened to the II and it is an pretty incredible piece.

The II has a different treble character than the original. It's more upfront and explicit. The II is not a hard sounding amp, if anything, the original is a little soft sounding.

Do an archive search, I remember somewhat was quite adamant about the original having a better build quality.

This is the first I have ever heard of anyone claiming better build quality on one over the other; having owned the II, I don't know what JRDG could of done to improve upon the build quality, it was second to none. I am sure JRDG would refute this claim.

I will throw in my hat as one who enjoyed the CN-II a lot, I know this doesn't address your question.

Here is a reply from Rich Maez from JRDG in answer to a question I had for him in the past.

"The CN I and CN II differ completely by power supply. The CN II has a much more powerful (50% more power) supply and therefore has much better control and power into low frequencies. It also has a separate front end supply that allows the unit to dedicate more power to large transients and make the CN II much more dynamic. High frequency distortion was reduced quite a bit with the second generation unit as well, so it has a much more open and extended high frequency response."