Acid catalyst choice on reaction of carbonyl group and O/N nucleophiles

For oxygen nucleophiles, e.g. $$\ce{ROH}$$, when reacting with a carbonyl group to form acetal, the acid catalyst used is protonated alcohol.

for nitrogen nucleophiles, e.g. $$\ce{RNH2/RR'NH}$$, when reacting with a carbonyl group to form imine/enamine, the acid catalyst used is $$\ce{NH4+}$$ instead of protonated alcohol.

According to both reaction mechanisms, both catalysts are just acting as $$\ce{H+}$$ donators & acceptors, so why 2 different acid catalysts need to be used? Can't I use protonated alcohol all the time?

• Where did you get the idea that NH4+ is the preferred catalyst? I find Ti(IV) species such at Ti(OiPr)4 the most effective. – Waylander Jul 2 '20 at 12:22
• @Waylander from 'Organic chemistry as a 2nd language 2nd semester', it told me ammonium ion is generally used as the catalyst. And sorry that I am just a beginner, when I look up the structure of Ti(OiPr)4 in Google, I don't know where is the ionizable proton. – 234ff Jul 2 '20 at 12:33
• – Mathew Mahindaratne Jul 2 '20 at 12:48
• @234ff You need a better textbook – Waylander Jul 2 '20 at 13:17
• Seems all my talking under earlier question was in vain... – Mithoron Jul 2 '20 at 16:58