marshall 2021 fuzz pedal project (help very much appreciated)

[Electric Warrior]

The only time I experienced crackling was with a faulty transistor.

The attack pot should be able to mellow it down quite a lot. But I'm not sure how it can be harsh and muffled at the same time?

Do yourself a favour and try the pedal through a tube amp. DI fuzz guitars tend to sound very fizzy.

Also, if you could measure some the voltages on your breadboard we could see if there is anything obviously wrong with it.

[Allanp]

Q1 C to ground = 9.33v
     B to ground = 0.02v
     E is to ground
Q2 C to ground = 0.44v
      B to ground = 0.08v
     E is to ground
Q3 C to ground = 6.60v
      B to ground = 0.43v
      E to ground = 0.34v

According to the seller, Q1 was hfe 78 with leak of .24, Q2 was hfe 94  with leak of .18, Q3 was hfe 101 with leak of .28, at least, I think that says leak, I can't quite read the handwriting.

I tried it though my vox ac15cc and it was less harsh but more kinda closed sounding. It's hard to explain, it's as if there's wax in your ears but with harsh overtones that cut through somewhere. Altering tone and volume guitar settings, level and attack breadboard settings and all the amp settings, I can get rid of most of the harshness but it's way too muffled, or I can open up the sound and it also brings the harsh harmonics, but even if I accept the harsh harmonics I still can't get the sound to open up enough.

[Electric Warrior]

That seems to be too little leakage for that bias setup with those hfes. Or is it cold where you're testing the circuit?
Try bigger resistors at Q1's base and Q2's collector.