THAT1646 balanced driver (pinout verified, THAT doc 600078 rev07) closes the chain:
MIX_OUT -> 25-turn level-cal trim -> THAT1646 (+6dB, sense tied local) -> 47ohm
build-out -> fail-safe mute relay K2 -> balanced AOUT_HOT/COLD on the interconnect;
ground-lift relay K3 (de-energized=bonded, soft-lift 100R||10nF) -> CHASSIS.
- Phase: Stage 3 inversion corrected via HOT<-OUT-, COLD<-OUT+.
- Level cal trim ahead of the driver (its +6dB gain is fixed).
- K2 fail-safe: de-energized shorts both legs to GND after the build-out (driver
current-limited). K3 ground-lift in series with a face panel switch.
- stage4_driver.cir: differential flat +4.76dB (1k=20k), legs antiphase (0 vs pi rad),
build-out+cable rolloff above audio. ERC 0 errors; netlist 0 errors.
AUDIO CHAIN COMPLETE: stages 1, 1b, 2, 3, 4 all captured + simulated + ERC-clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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