Hypophonia is a common speech impairment associated with Parkinson's disease (PD). Voice amplifiers are typically used to increase voice loudness, but little is known about their impact on perceived speech quality. In this paper, speech recordings were obtained from 11 PD subjects with and without the use of seven different amplification devices, and in the absence or presence of background noise. The recorded speech samples were rated for their sound quality by 10 naive listeners. The same speech recordings were analyzed objectively, where in linear prediction, mel-frequency cepstral coefficients (MFCCs), and gammatone cepstral coefficients (GFCCs) were extracted and mapped to predicted quality scores using linear regression and Support Vector Regression (SVR). Results showed that amplification devices differentially affect the perceived quality of PD speech, that objective and subjective quality scores correlated well, and that a reduced set of GFCC features mapped with SVR produced the best correlation with the subjective scores.