External Timing Source

Hi All,
I was wondering if someone can recommend a good external Timing source for FreePBX?
We recently migrated from TrixboxCE and used to use a Sangoma USB UT50.

Maybe the timing source is no longer necessary?

Currently using Distro Stable-2.210.62-6 Release Date-03-17-13.
Environment is approx 10 phones with working QoS on cisco router and ample bandwidth.
No users have complained about voice quality but i would also like to keep it this way.

Dahdi_test output is below:

— Results after 508 passes —
Best: 100.000% – Worst: 99.601% – Average: 99.943448%
Cummulative Accuracy (not per pass): 99.999