Here’s some info on my amp:
3.5V RMS input volts to drive the output stage to full power. That is with 7.8 dB feedback. If I were to run mine open loop, it would require about 1.4V RMS.
THD at full power (14 watts), with feedback loop closed: 2.3% at 50Hz, 0.82% at 1 KHz, 1.6% at 20 KHz.