The 301 and 401 ARE different than the 300 and 400. From the 200 down they are the same. The 200 and 201 are the same as John said above.. The 301 and 401 use a different curcuit than the 300 and 400. The cam also uses this new curcuit. There will be a difference in sound between your 400 and 401. What the difference is and how much of an improvement if any should be determined by your own ears. I never listened to the difference. Everything is the same design except using a different curcuit. They still employed the same design using more smaller caps rather than fewer larger caps. The 301 and 401 uses the same combination of Bi-polar, Mosfet and J-Fet Transistors. So John was right and wrong. His ca200 and the newer ca201 are exactly the same under the hood with only a face lift. The ca300 and ca400 are very similar but a little different under the hood. The 300 and 400 were always different from the 200 and under. Its like you stepped into a higher league once you stepped up to the ca300 from the ca200. From the 200 down its like stepping down a step. The CAV 75 and 150 series of multi Channel amps are the same under the hood with only a face plate change.
Hope this helped.
Hope this helped.