The OPAx134 series of operational amplifiers have excellent distortion characteristics. THD+Noise is below 0.0004% throughout the audio frequency range, 20Hz to 20kHz, with a 2kΩ load. In addition, distortion remains relatively flat through the wide output voltage swing range, providing increased headroom compared to other audio amplifiers, including the OP176/275.

Headroom is a subjective measurement, and can be thought of as the maximum output amplitude allowed while still maintaining a low level of distortion. In an attempt to quantify headroom, TI defines very low distortion as 0.01%. Headroom is expressed as a ratio which compares the maximum allowable output voltage level to a standard output level (1mW into 600Ω, or 0.7746Vrms). Therefore, OPA134 series of operational amplifiers, which have a maximum allowable output voltage level of 11.7Vrms (THD+Noise < 0.01%), have a headroom specification of 23.6dBu. See Figure 5-4.