What is the maximum length of xlr cable from a Canon XA10 to a microphone without losing quality of sound
Assuming you have a well-shielded cable construction, adequate common-mode rejection, no ground-loops, and thus being able to ignore environmental noise pick-up by the cable. It is rather simple to estimate. 

Assumptions:


Driver output impedance &lt;100ohm
Driver is stable under large capacitive loads. 
Receiver input impedance >1kohm||100pf
Cable pair capacitance &lt;100pF/m
cable AWG&lt;32 (limiting resistive losses)
Bandwidth of interest &lt;40kHz (1/2 power pole location)


You can thus estimate that the maximum distance would be >400m, which is the limit due to the low-pass characteristic of the output impedance driving the large capacitance of the cable. 

Interestingly, that is approaching the maximum distance you can get away with without having to worry about properly terminating the cable. 

As the driver is using phantom power, the simpler amplifier design would have an output impedance that could be more than an order of magnitude larger, which would limit the distance to &lt;40m. 

However, the limit will likely be less due to common mode noise pick-up mostly due to ground loops. But this can be addressed separately.