Electric guitar preamp K4102 squealing

Hi,

Yesterday I finished assembling the guitar preamp kit and as I connected the guitar and headphones, I heard a deafening high-pitched squeal from the headphones. It came and went away as I turned the volume knob on the preamp. Can anyone help me find the cause of the problem? Btw, not having a mono guitar connector/adapter, I connected the right channel connector to the preamp. Could this cause problems?

Thanks!

Check your assembly.
A wrong resistor value or soldering error can cause the circuit to oscillate.