LM386 PCB Design Guide: Footprint, Pinout, and Alternatives
Low-voltage mono audio power amplifier with pin-settable gain of 20 to 200.
The LM386 is a mono class-AB audio power amplifier built for low-voltage, minimum-part-count designs. The gain is internally set to 20 (26 dB), an external capacitor or RC between pins 1 and 8 raises it anywhere up to 200 (46 dB), and the whole thing runs from a 4 to 12 V single supply (5 to 18 V for the LM386N-4 grade) on 4 mA of typical quiescent current. It drives speakers down to 4 Ω directly: the SOIC-8 part is specified at 325 mW typical into 8 Ω at 6 V and 10% THD, with distortion at normal listening levels around 0.2% typical at 125 mW.
Pick it for what it still does best: a working speaker amplifier from a single supply and a handful of passives, with decades of proven application circuits behind it. Do not pick it for battery or low-rail designs; modern rails sit below its 4 V minimum, its class-AB output burns power the speaker never sees, and it needs a 250 µF coupling capacitor in series with the speaker that bridge-tied parts like the LM4871 delete outright. And despite the schematic symbol and the category it lives in here, it is not a general-purpose op-amp: the feedback network is internal, and the inputs are ground-referenced with a ±0.4 V absolute maximum.
Most LM386 boards that misbehave share the same handful of mistakes: DC-coupling a signal into those ±0.4 V ground-referenced inputs, leaving pin 7 unbypassed and earning hum or motorboating, omitting the 0.05 µF + 10 Ω output snubber and getting supersonic oscillation, expecting the half-watt PDIP spec from a SOIC-8 at 6 V, and wiring the gain-200 configuration with long unshielded input leads. Each one is covered below.
What breaks boards
It is not an op-amp: inputs are ground-referenced with a ±0.4 V absolute maximum
The feedback network is internal — an on-chip resistor sets the gain at 20 (26 dB) — so you cannot close your own loop around it, and both inputs are biased to ground through internal 50 kΩ resistors. Absolute maximum input voltage is −0.4 to +0.4 V. DC-couple a line-level source, or any signal referenced above ground, and you exceed that rating on every peak. AC-couple anything larger, give the source a DC return to ground, and treat pins 2 and 3 as an audio input, not op-amp inputs.
An unbypassed pin 7 turns supply ripple into hum and motorboating
Pin 7 (BYPASS) decouples the internal bias network, and it is the difference between a quiet amplifier and one that sings along with its supply. With 10 µF on pin 7, PSRR is 50 dB typical at 1 kHz referred to the output; the datasheet's Figure 6-2 shows the no-bypass-capacitor curve sitting far below every bypassed one. On a shared rail the symptom is hum; on a sagging battery it is low-frequency motorboating. Fit 10 µF from pin 7 to ground plus a supply capacitor close to pin 6, per TI's power supply recommendations.
Skip the 0.05 µF + 10 Ω output snubber and it can oscillate
Every typical-application circuit in the datasheet — and all three layout examples — includes a series RC of 0.05 µF and 10 Ω from the output pin to ground. It keeps the output stage stable into the speaker's inductive load. Omit it and the amplifier can oscillate above the audio band: the symptoms are a hot package, elevated supply current, and gritty distortion rather than an audible squeal. Keep the snubber and the 250 µF output coupling capacitor tight to pin 5, keep the speaker traces short, and route the analog input away from digital traces.
The SOIC-8 is not the half-watt part
The famous 500 mW min / 700 mW typ output spec belongs to the PDIP LM386N-3 at 9 V into 8 Ω at 10% THD. The SOIC-8 orderables (LM386M-1/MX-1) are specified at 250 mW min / 325 mW typ at 6 V, and the package physics back that up: 0.73 W absolute-maximum dissipation and an RθJA of 115.7 °C/W, versus 1.25 W and 53.4 °C/W for the PDIP. If the design needs the classic half watt into 8 Ω, use the PDIP N-3 on a 9 V rail — or admit it is a class-D job.
Gain of 200 amplifies your layout, not just your signal
A 10 µF capacitor from pin 1 to pin 8 lifts the gain from 26 dB to 46 dB, and at that gain the input side dominates everything. The inputs bias through 50 kΩ with about 250 nA of bias current, so an unused input left floating degrades gain and invites instability: bypass it with 0.1 µF or short it to ground, depending on the driven source's DC resistance. The driven input needs a short, quiet path — at a gain of 200, hum and RF picked up on a long input lead come out of the speaker at full volume.
Key specifications
| Parameter | Value | Source |
|---|---|---|
| Supply range | VCC 4 V min / 12 V max (LM386N-4 grade: 5 V min / 18 V max); speaker impedance 4 Ohm min; TA 0 to 70 C | SNAS545D Rev D, Section 6.3 Recommended Operating Conditions |
| Quiescent current | 4 mA typ / 8 mA max (VS = 6 V, VIN = 0) | SNAS545D Rev D, Section 6.5 Electrical Characteristics, IQ row |
| Output power | 250 mW min / 325 mW typ (VS = 6 V, RL = 8 Ohm, THD = 10%; LM386N-1, LM386M-1, LM386MM-1); 500 mW min / 700 mW typ (VS = 9 V, RL = 8 Ohm, THD = 10%; LM386N-3); 700 mW min / 1000 mW typ (VS = 16 V, RL = 32 Ohm, THD = 10%; LM386N-4) | SNAS545D Rev D, Section 6.5 Electrical Characteristics, POUT rows |
| Voltage gain | 26 dB typ (VS = 6 V, f = 1 kHz); 46 dB typ (10 uF from Pin 1 to 8); gain settable 20 to 200 via pins 1/8 | SNAS545D Rev D, Section 6.5 Electrical Characteristics, AV rows + Section 1 Features (Voltage Gains from 20 to 200) |
| THD | 0.2% typ (VS = 6 V, RL = 8 Ohm, POUT = 125 mW, f = 1 kHz, Pins 1 and 8 Open) | SNAS545D Rev D, Section 6.5 Electrical Characteristics, THD row |
| Absolute maximum ratings | Input voltage VI: -0.4 V min / 0.4 V max (the spec that bites people - inputs are ground-referenced, AC-couple larger signals); supply VCC: 15 V max (LM386N-1/-3, LM386M-1), 22 V max (LM386N-4); storage temp -65 to 150 C | SNAS545D Rev D, Section 6.1 Absolute Maximum Ratings |
| Thermal / dissipation | Package dissipation (abs max): 1.25 W (LM386N), 0.73 W (LM386M), 0.595 W (LM386MM-1); RthetaJA: 115.7 C/W (D SOIC-8), 169.3 C/W (DGK VSSOP-8), 53.4 C/W (P PDIP-8) | SNAS545D Rev D, Section 6.1 Absolute Maximum Ratings (Package Dissipation rows) + Section 6.4 Thermal Information (RthetaJA row) |
| PSRR | 50 dB typ (VS = 6 V, f = 1 kHz, CBYPASS = 10 uF, Pins 1 and 8 Open, Referred to Output); Figure 6-2 plots supply rejection for Pin 7 bypass capacitors of 0.5 uF to 50 uF against a far lower no-bypass-capacitor curve | SNAS545D Rev D, Section 6.5 Electrical Characteristics, PSRR row + Figure 6-2 Power Supply Rejection vs Frequency |
| Input stage | Input resistance 50 kOhm typ; input bias current 250 nA typ (VS = 6 V, Pins 2 and 3 Open); both inputs are biased to ground through internal 50-kOhm resistors; at higher gains, bypass the unused input with a 0.1 uF capacitor or short it to ground depending on the DC source resistance | SNAS545D Rev D, Section 6.5 Electrical Characteristics (RIN, IBIAS rows) + Section 9.2.1.2.2 Input Biasing |
| Output network | 0.05 uF in series with 10 Ohm from VOUT to ground plus a 250 uF output coupling capacitor to the speaker, in every typical-application circuit and layout example; the gain-200 and AM-radio circuits add 10 uF from Pin 7 (BYPASS) to ground | SNAS545D Rev D, Figures 9-1, 9-3, 9-13 + Section 11 Layout, Figures 11-1 to 11-3 |
Verified against the manufacturer datasheet on 2026-07-10. Confirm the current revision before production use.
Alternatives
- LM4871: 3-W mono class-AB with a bridge-tied-load output — no output coupling capacitor — plus a shutdown pin; 2.0–5.5 V supply, the natural choice on modern low-voltage rails.
- PAM8403: Diodes Inc. filterless 3-W class-D stereo at 5 V; far higher efficiency than the class-AB LM386, and the common hobbyist substitute.
- TPA6211A1: 3.1-W mono fully differential class-AB, 2.5–5.5 V; TI's modern replacement for battery-powered designs.
- LM380: the classic 2.5-W sibling with a fixed gain of 50, for higher supply rails (10–22 V) where the LM386 runs out of output power.
Common questions
- How much power can an LM386 actually deliver?
- It depends on the grade and supply: 250 mW min / 325 mW typ at 6 V into 8 Ω (10% THD) for the LM386N-1, M-1, and MM-1; 500 mW min / 700 mW typ at 9 V into 8 Ω for the LM386N-3; and 700 mW min / 1 W typ at 16 V into 32 Ω for the LM386N-4. The half-watt reputation assumes the PDIP N-3 on a 9 V rail — the SOIC-8 at 6 V is a 325 mW amplifier.
- What supply voltage does the LM386 need?
- 4 to 12 V recommended for the LM386N-1/-3 and M-1 variants, and 5 to 18 V for the LM386N-4, at 4 mA typical quiescent current. Absolute maximum supply is 15 V (22 V for the N-4), and the recommended minimum speaker impedance is 4 Ω.
- How do I change the LM386's gain?
- Through pins 1 and 8. Left open, the internal resistor sets a gain of 20 (26 dB). A 10 µF capacitor from pin 1 to 8 gives the maximum gain of 200 (46 dB), and a resistor in series with that capacitor sets any value from 20 to 200. At higher gains, bypass pin 7 with 10 µF and deal with the unused input: 0.1 µF to ground or a short, depending on source resistance.
- Why does my LM386 hum or motorboat?
- Almost always a missing pin 7 bypass capacitor: with 10 µF there, PSRR is 50 dB typical at 1 kHz; with nothing, supply ripple feeds straight through to the output. If it buzzes or runs hot rather than hums, check for the 0.05 µF + 10 Ω output snubber — without it the amplifier can oscillate above the audio band.