The main difference is that Bnai Yisrael as a mob, forced Aharon to build the egel in order to replace Moshe Rabbeinu when they panicked after (they thought) he was late returning from Har Sinai.
When the people saw that Moses was late in coming down from the mountain, the people gathered against Aaron, and they said to him: "Come on! Make us gods that will go before us, because this man Moses, who brought us up from the land of Egypt we don't know what has become of him."
As soon as Moshe returned, the people abandoned all thought of the idol. Only three thousand out of the 600,000 actually deserved the full punishment as we see in Ki Sisa 32:28
The sons of Levi did according to Moses' word; on that day some three thousand men fell from among the people.
On the other hand Yerav'am built the idols with malice aforethought in order to prevent the people from returning to the temple. He built one at each border (north and south) in order to make sure that they would find it easier to perform the worship that he made up. He also created a new festival in the month after Succos in order to make sure that they would not continue going to Yerushalayim.
28 The king took counsel and made two golden calves, and he said to them, saying, "It is far for you to go up to Jerusalem; here are your gods, O Israel, that have brought you up from the land of Egypt."
33 And he brought up offerings on the altar which he has made in Beth El on the fifteenth day of the eighth month, in the month that he had fabricated from his heart, and he made a festival for the children of Israel, and he went up to the altar to burn the incense.