Control volume with a pot
Does your circuit pass sound with the 1uF capacitor removed?  If not, then you have some fundamental problem with your "output buffer" circuit.

Using a shunt transistor (your BC549) to control audio signals is an old trick from decades ago in cheap tape recorders, etc.  It is not a proper level control in the modern sense.  There are plenty of voltage-controlled amplifier circuits and digital pots that would be a proper way to do this here in the 21st century.