I was curious too, after i read your post. Here's some AI-Stuff about that:
"Official EMG datasheets indicate a shift in the resonant frequency of the EMG 81, lowering it from 2.25 kHz to 1.63 kHz, which creates a more congested mid-hump. Additionally, the transition from older, slower op-amps (like the LM4250) to modern, faster SMD components has removed the soft-clipping characteristics, resulting in a more abrasive and sterile tone in newer models."
View attachment 441738
Summary of the Op-Amp Change
The core of the sonic shift is the replacement of the legacy
LM4250 Op-Amp. This chip was a "programmable" micropower amplifier that allowed EMG to set a specific
Slew Rate. This resulted in a natural, tube-like compression and a resonant peak at
2.25 kHz, providing that classic "liquid" lead tone.
Modern units have transitioned to high-efficiency SMD (Surface Mount) components. While these are technically "better" (lower noise floor of -100 dBV), they lack the characteristic saturation of the old chips. The shift of the resonant peak down to
1.63 kHz creates the "mid hump" you described, losing the high-end clarity and making the pickup feel more
abrasive and less musical to the ears of vintage enthusiasts.