hi guru,
i received the logarithmic pot that i mentioned before. It still results to the same poor result. which is something like below:

max resistance for the 10k POT is 9.79k ohm
resistance between input and C1 = 9.79k ohm very low sound
resistance between input and C1= 9.72k ohm the best volume
resistance between input and C1= 9.82k ohm suddenly very loud


i tried to observe the waveform at the C1 negative leg, the sine wave rise slowly with a very low Vp-p which is around a few milivolts.

Could it be something wrong with the boostrapped part?

thank you.

 

Disconnect the input and measure the resistance of the slider of the pot to ground when the pot is adjusted to half-way. If it is about 4.9k then it is a linear pot which makes a poor volume control.
If it is 500 ohms to 2k then it is a logarithmic audio taper volume control.

The bootstrapping has nothing to do with the input sensitivity to the volume control.

The input of the amplifier is very simple. Its negative feedback from R3 and C3 is affected by the volume control which is bad. When the volume control is turned down then the negative feedback is also turned down which increases the gain of the amplifier which is bad.
Add a 10k resistor in series with C1 to fix it.