The scant manual of the Acurus A250 and 200X3 I use to power a 5.1 set-up recommends a break-in period of about 250 hours to bring it to optimum performance.
There may be some debate on whether power filter caps charge faster after repeated use, thereby improving transient response, or that repeatedly heating the transister could bring it to optimum performance. I personally do not believe SS amps need break-in. But what the heck. Either 250 hours will break it in or I'd get accustomed to the sound
Either way, I now am in love with it.
Going from a 45 watt/ch stereo receiver to a 100 watt/cha amp should yield some discernible difference in apparent volume. This is almost a 3db improvement. Same when I shifted from an Onkyo Integra 120 watt/ch receiver to the Acurus 250 watt/channel amp.
Offhand I should say that right out of the box, given the same volume setting you use for normal listening, the new amp should give an apparent increase in SPL (a doubling of power yields a 3db increase in volume, not SPL; an apparent doubling of SPL requires 6db increase or quadrupling of power)
But if your anticipated impression turns out underwhelming, there are variables to consider:
(1) Your amp may be starved of the needed electrical power from your AC mains. While your AC outlet may have been sufficient with your old receiver, the new amp may be more power hungry. The manual of my Acurus amps strongly recommends I connect them to dedicated AC outlets, with no other appliance sharing it. But that's because each amp consumes 1.2kva of electricity - about the same as a 1HP aircon. I don't know about Carver.
(2) Your speakers make have worked well with the old receiver but could be less enthusiastic with its new amp. It is sometimes not enough to match the two in terms of impedance and power handling. Consumer mass hi-fi equipment do not have this problem. But as you go up, the more exotic brands could be more choosy and sensitive. If not mistaken, Carver is in that league. HK is not. Speakers generally have unique capacitive and inductive reactances that some amps may be better handling than others. Then there is this damping factor in amps that may over-control speakers that already have sufficient internal damping to begin with, thus, yielding too tight a bass or weak bass.
(3) Last but not the least, consider matching the preamp with the amp. The reciever's preamp may be perfectly suited to drive its internal amp but not so when connected to an external amp. If the Carver needs 2 volts of input to drive it to full rated power, connecting it to a preamp whose output voltage is only 1 volt will drive the amp to only half its rated power at full volume. This may be the cause of your underwhelming impression of the Carver with the HK preamp. I wouldn't worry about the impedances. Most of them are within each other's range. Typically, preamps have output impedances of 22kohms, while amps have input impedances slightly higher up to 50kohms. Do refer to the manuals of your HK and Carver as they should indicate these voltages in RMS. If the disparity in voltage is great, then you have a problem - I would suggest you get a new preamp with the right output voltage.
