Cobain used a Boss DS-1 into a Mesa Boogie Studio preamp. Simple but aggressive. High gain, slightly scooped.
Signal Chain
Boss DS-1→Mesa Boogie Studio Preamp→4x12 V30→Output
PedalBoss DS-1
gain
8
tone
5
level
7
AmpMesa Boogie Studio Preamp
bass
6
gain
6
mids
4
treble
7
presence
5
Cab / IR4x12 V30
micSM57
mic positioncenter cap
Notes
The verse is clean-ish, the chorus is massive. Use the DS-1 for the chorus only.
Don't have Helix?
See the same signal chain mapped to another platform. Knob values carry over as starting points — gain ranges differ between platforms. NAM/TONEX users: the real gear names are what to search for as captures.