printf>stdin unusable with read

With read, sending "a" to stdin is not equivalent to pressing "a" (or use your favorite letter/key).

Tested this:

~$ read -n1 & fg
[1] 11620
read

Then "typed" "a" into the read process stdin (in another console):

~$ printf "a" >/proc/11620/fd/0

How do I make the stdin method equivalent to direct typing? Should I add some special control character, like:

~$ printf "a\x04" >/proc/11620/fd/0  # didn't work either