Crackle on Big Muff tone pot

[Seljer]

I made a big muff about three years ago and as far as I can remember, the tone control always crackled a bit during adjustment. I always thought that I had a bad pot and just couldn't be bothered to replace it.

But today, it just occurred to me that theres no DC blocking capacitor after the third transistor stage before the tone control. So if the emitter is at about 4V, through the tone stack, one end of the tone potentiometer is at roughly 3V, the other end about 1V. Is the crackle I'm getting from this DC flowing over it or is the potentiometer really bad?

[LucifersTrip]

the cap in the tone control doesn't take care of that?  I don't remember any crackle in any of my muffs

[amz-fx]

But today, it just occurred to me that theres no DC blocking capacitor after the third transistor stage before the tone control. So if the emitter is at about 4V, through the tone stack, one end of the tone potentiometer is at roughly 3V, the other end about 1V. Is the crackle I'm getting from this DC flowing over it or is the potentiometer really bad?

Yes, the dc in the tone pot is causing the swish sound as the knob is rotated. You can add a 1uF capacitor between the collector of Q3 and the input of the tone control network to prevent the noise.

Best regards, Jack