BA3121F-E2 from ROHM, in a SOP-8. Pinout and pin descriptions extracted from the manufacturer datasheet by ds2sf; symbol, footprint, and 3D from KiCad-official CAD.

Pinout

Pin	Name	Type	Function
1	OUT1	output	Channel 1 audio output. Drives the power amplifier through a coupling capacitor (typ. 4.7 µF electrolytic). Ground-isolated version of the IN1 signal.
2	VM1	passive	Channel 1 common-mode rejection setting/decoupling node. External capacitor to ground (typ. 22 µF) sets the CMRR performance for amplifier 1-A. Larger capacitance improves low-frequency CMRR.
3	IN1	input	Channel 1 audio input from the source (tape deck / tuner). AC-coupled via an external 4.7 µF capacitor. Typical input resistance 55 kΩ.
4	GND	power_in	Ground reference (car body ground on the source side). All internal circuitry is referenced to this pin.
5	IN2	input	Channel 2 audio input from the source (tape deck / tuner). AC-coupled via an external 4.7 µF capacitor. Typical input resistance 55 kΩ.
6	VM2	passive	Channel 2 common-mode rejection setting/decoupling node, shared with the reference divider. External capacitor to ground (typ. 10 µF) sets CMRR performance for amplifier 2-A.
7	OUT2	output	Channel 2 audio output. Drives the power amplifier through a coupling capacitor (typ. 4.7 µF electrolytic). Ground-isolated version of the IN2 signal.
8	VCC	power_in	Positive power supply. Recommended operating range 4 V to 18 V (typ. 12 V), absolute maximum 18 V. Quiescent current ~9.0 mA typ.

Key specifications

Parameter	Value
Manufacturer	ROHM
Package	SOP-8
Category	Op-amp/Cmp
Pins	8

Ordering variants

BA3121F-E2

CAD (KiCad official)

Symbol: BA3121F-E2
Footprint: Package_SO:SOIC-8_3.9x4.9mm_P1.27mm
3D model: SOP-8 (KiCad packages3D, STEP)

3D model downloads

Two STEP files. Same geometry, different body top:

File	Size	Use it when
`ba3121f-e2.step`	122 KB	You want the bare part, or you mark your own boards.
`ba3121f-e2-etched.step`	1.8 MB	You want the part with `BA3121F-E2` already on it.

The marking in the etched file is real recessed geometry cut into the solid, not a texture or a decal: 474 faces against 147 in the bare model. It survives export, section views, and rendering in any CAD tool, and it drops straight into KiCad or Fusion with no extra setup.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: ROHM datasheet (15 pp, sha256 a0c13e55a1f7debc, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF