TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6269
Posted: 10:09pm 02 Jul 2021
The original design was for line level output and that hasn't changed. 4.7k is the usual impedance for line level.
I did do some tests to see what minimum resistance was needed to prevent distortion at the processor end but can't readily find the info. It's somewhere here on TBS.
To date, the vast majority of users have used PC powered speakers and 4.7k gives a good match to their typical 100 ohm to 2k input impedance while keeping the line level specs satisfied.
There is nothing to stop you bypassing the 4.7k with whatever value you desire but to drive low impedance speakers, a voltage follower or similar would be required.