You need to determine if the distortion is because of:
1/ Applying to much signal to the input.
2/ You have a construction error somewhere such as an incorrect value resistor.
3/ That the circuit is suddenly going unstable as amplitude from the first stage increases.
This really needs a scope although you can do basic level checks with an AC range on a DVM. If you are running on -/+12 volt or higher rails then you should get no distortion with the controls centred and an output of 7 or 8 volts rms as measured at the output of the first opamp. That's a lot of signal.
1/ Applying to much signal to the input.
2/ You have a construction error somewhere such as an incorrect value resistor.
3/ That the circuit is suddenly going unstable as amplitude from the first stage increases.
This really needs a scope although you can do basic level checks with an AC range on a DVM. If you are running on -/+12 volt or higher rails then you should get no distortion with the controls centred and an output of 7 or 8 volts rms as measured at the output of the first opamp. That's a lot of signal.