Will there be a dramatic difference?

I believe that is the name of the company.  The owners manual will give you the info you need.

I had a couple Carver amps back in the day.  Pretty good for 35 yrs ago and decent prices. The A 21+ is on the warm side sound wise like the Carver.

I have an A21+. What I really like about it is that if you hook up dual subwoofers to it, the gain adjustments allows you to tune it just like you like it. Reason is the lower you set the gain will diminish the mids and trebles much more than the lows. Hence it is an easy way to tune it to your ears. My best average adjustment, so it will sound best with all my different sources, Vinyl, CD, DVD, tuner and streamer is at 2pm, meaning basically two thirds gain. Enjoy, I do.

My A21 arrives today…. Pretty excited. But now all you guys have me thinking about fuses, power conditioners and power plugs… ugggh I’m gonna go bankrupt with this hobby!!!!  I hear the A 21+ takes about 40 hours of play to really break in and start sounding good. I’ll keep everyone posted.

You'll really enjoy the A21, which on its own is great. Of course the JC5 in my experience is a major step up in every way, but comes at a higher price.

I've seen a few JC5s used for sale for really good prices lately so you could keep an eye out for a good deal that way.

If you are considering a used JC5 then you should also consider a used CODA #8. It's just as good or better than the JC5 and has a transferable 5-year warranty. This amp has massive current reserves.