I cannot tell how the pronunciations of 'ca' and 'ĉa' are different. For me, they sound the same. (I am a native Korean speaker.)
Mi ne povas distingi la diferencon 'ĉa'r mi estas komen'ca'nto.
In the Wiktionary, the pronunciations of the above are t͡sa for 'ca' and t͡ʃa for ĉa which sound almost the same to me.
The buzzing sounds in Esperanto, ĉ, ĝ, ĵ, ŝ and z, can be hard to distinguish one from another depending on one's native language.
When it comes to pronouciation of ca vs. ĉa, it helps to remember that the plain s in Esperanto is very sharp, like the s-es in the English word "issue". So ca has that shap s (tsa), while ĉa has the buzzing s (tsha).
The sound starts with a t and then respectively sa ("ca") or ŝa ("ĉa"). The ŝa is a sharp open sound, like she in English. And sa would be like see in English.
Now by preceding the sounds with a t you might recognize the difference, at least in pronouncing. Recognizing a difference in one self pronouncing the sound can sometimes be corrected by recording ones own pronunciation. Reason: a human hears its own voice physically a bit differently.
Honestly the difference in sound might be much less, than the difference in articulation to form the sound. ŝ is blowing between open teeth, s is more closed. The IPA phonetic symbols are better explained by others.
