This paper investigates the symbol error rate (SER) performance of cell-free large scale multiple input multiple output (MIMO) systems, specifically focusing on scenarios involving maximum-ratio combining (MRC) detectors and perfect channel state information (CSI) under Rayleigh fading channels. First, the study begins by deriving the probability density function (PDF) for both the desired signals and the equivalent noise. These derivations are carried out for two common modulation schemes: M-ary phase shift keying (PSK) and M-ary pulse amplitude modulation (PAM). On the basis of these PDF derivations, this paper further develops analytic expressions for the SER of both modulation techniques. The final section presents numerical simulations that validate the accuracy of the derived SER expressions for these two modulation methods, confirming their consistency with the theoretical predictions.