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<header class="hero"><div class="eyebrow">Bench Notes / 01 · Stereo Audio</div><h1>Build a stereo amplifier on a breadboard.</h1><p>Two classic LM386 low-voltage power amplifiers turn a line-level music signal into speaker-level audio. One IC handles the left channel and one the right: a compact, battery-friendly first amplifier with independently mixed stereo volume control.</p><div class="badges"><span class="badge">9 V DC</span><span class="badge">2 × LM386</span><span class="badge">8 Ω speakers</span><span class="badge">Beginner friendly</span></div></header>
<nav class="toc" aria-label="Guide sections"><a href="#safety">Safety</a><a href="#parts">Parts list</a><a href="#diagrams">Diagrams</a><a href="#assembly">Assembly</a><a href="#testing">Test & troubleshoot</a></nav>
<section id="intro"><h2><span class="num">00</span>Signal in, sound out</h2><p class="lead">An LM386 is a small mono audio power amplifier. Its non-inverting input receives an AC-coupled audio signal; internal gain amplifies it, and a large output capacitor protects the speaker from DC. Build the same proven circuit twice, share the 9 V supply and ground, then route the left and right contacts of a 3.5 mm source through a dual-gang volume pot.</p><div class="warning"><strong>Design note —</strong> This guide uses low power (about 0.3–0.7 W/channel). It is ideal for efficient 8 Ω speakers at desktop volume, not headphones or large hi-fi drivers.</div></section>
<section id="safety"><h2><span class="num">01</span>Safety & prerequisites</h2><div class="grid"><article class="card"><h3>Workbench rules</h3><ul><li>Disconnect the 9 V supply before moving wires or capacitors.</li><li>Observe electrolytic polarity: the striped lead is <span class="pin">−</span>. A reversed capacitor can vent or fail.</li><li>Use a regulated 9 V supply or fresh 9 V battery. Never use mains voltage.</li><li>Start at minimum volume; avoid shorting the speaker leads or supply rails.</li></ul></article><article class="card"><h3>Tools & baseline knowledge</h3><ul><li>Solderless breadboard, solid-core jumpers, wire cutters/strippers, and a multimeter.</li><li>Audio source with 3.5 mm cable/breakout; two 8 Ω speakers.</li><li>Optional: soldering iron only if making a permanent lead or jack adapter.</li><li>Recognize resistor color/value markings, capacitor polarity, IC notch orientation, and breadboard connected rows.</li></ul></article></div></section>
<section id="parts"><h2><span class="num">02</span>Complete parts list</h2><div class="table-wrap"><table><thead><tr><th>Component / part number</th><th>Qty.</th><th>Purpose / role</th></tr></thead><tbody><tr><td>LM386N-1 low-voltage audio power amplifier, DIP-8</td><td>2</td><td>One mono power stage per left/right channel.</td></tr><tr><td>10 kΩ dual-gang logarithmic potentiometer</td><td>1</td><td>Master stereo volume; use two 10 kΩ pots if dual-gang is unavailable.</td></tr><tr><td>10 µF electrolytic capacitor, ≥16 V</td><td>4</td><td>Two input coupling capacitors + two gain capacitors (pins 1–8).</td></tr><tr><td>220 µF electrolytic capacitor, ≥16 V</td><td>2</td><td>DC-blocked speaker outputs.</td></tr><tr><td>100 nF ceramic + 100 µF electrolytic</td><td>1 each</td><td>Shared supply decoupling; fit close to ICs.</td></tr><tr><td>10 Ω resistor + 47 nF capacitor</td><td>2 each</td><td>Output Zobel networks for stable high-frequency operation.</td></tr><tr><td>8 Ω speakers, 1 W or greater</td><td>2</td><td>Left and right sound output.</td></tr><tr><td>9 V battery + clip or regulated 9 V DC supply</td><td>1</td><td>Power source.</td></tr><tr><td>Breadboard, jumpers, 3.5 mm TRS breakout/jack</td><td>1 set</td><td>Prototyping and stereo source connection.</td></tr></tbody></table></div></section>
<section id="diagrams"><h2><span class="num">03</span>Circuit diagrams</h2><div class="diagram">${schematic()}</div><p class="caption">Figure A — Repeat the highlighted LM386 channel for LEFT and RIGHT. All ground symbols join the blue ground rail.</p><div style="height:18px"></div><div class="diagram">${breadboard()}</div><p class="caption">Figure B — Visual placement map. The center trench keeps each DIP-8 pin on its own breadboard row. Connect matching colored nets exactly once per channel.</p></section>
<section id="assembly"><h2><span class="num">04</span>Step-by-step assembly</h2><div class="steps"><article class="step"><h3>Prepare the power rails</h3><p>Link split red rails together and split blue rails together. Connect the battery clip <code>+9V</code> to red and <code>GND</code> to blue. Keep the battery disconnected for now.</p></article><article class="step"><h3>Place both LM386 ICs</h3><p>Straddle the center trench with notches facing up. The notch identifies the top: pin 1 is top-left, pin 8 top-right. Reserve the left IC for <span class="mono">L</span> and right IC for <span class="mono">R</span>.</p></article><article class="step"><h3>Wire power and decoupling</h3><p>For each IC connect pin <code>6 → +9V</code> and pin <code>4 → GND</code>. Place 100 nF ceramic and 100 µF electrolytic across the rails; the 100 µF positive lead goes to +9 V.</p></article><article class="step"><h3>Set gain and bypass</h3><p>Place a 10 µF capacitor from pin <code>1 (+)</code> to pin <code>8 (−)</code> on each IC for high gain. Connect pin <code>7</code> to ground with a 10 µF capacitor, positive lead at pin 7.</p></article><article class="step"><h3>Add the volume control and input</h3><p>TRS sleeve goes to GND; tip is Left and ring is Right. Feed each through a 10 µF input capacitor (positive toward pot/IC). Pot outer lug goes to signal, other outer lug to ground; each wiper goes to its IC pin <code>3</code>. Tie pin <code>2</code> to ground.</p></article><article class="step"><h3>Connect outputs and speakers</h3><p>From each pin <code>5</code>, fit 220 µF with <strong>positive at pin 5</strong>; its negative lead goes to the speaker + terminal. Speaker − returns to GND. Add the 10 Ω + 47 nF series Zobel from pin 5 to GND.</p></article></div><div class="callout"><strong>Before power:</strong> use continuity mode to confirm red and blue rails are not shorted. Check each IC’s pin 6 is +9 V and pin 4 is ground. Recheck every electrolytic stripe.</div></section>
<section id="testing"><h2><span class="num">05</span>Testing & troubleshooting</h2><div class="grid"><article class="card"><h3>Safe first power-up</h3><ol><li>Set volume fully down and disconnect the audio source.</li><li>Power the circuit; measure near each IC: pin 6 ≈ 9 V, pin 4 = 0 V.</li><li>Measure pin 5: it should sit near half the supply. The speaker side of each 220 µF should be near 0 V DC.</li><li>Connect source, play a quiet track, then raise volume slowly.</li></ol></article><article class="card"><h3>Isolation trick</h3><p>If only one channel fails, swap the input leads at the potentiometer. If the fault moves, it is source/input wiring; if it stays, inspect that channel’s IC, output capacitor, and speaker wiring.</p></article></div><div style="height:18px"></div><div class="trouble"><div class="issue">No sound</div><div>Verify source output, common TRS sleeve ground, pin 3 signal path, and speaker return. Check the pot wiper is used—not an unused lug.</div><div class="issue">Hum or buzz</div><div>Use one common ground rail; keep input wires short and away from pin 5/speaker wires. Add/verify rail decoupling capacitors.</div><div class="issue">Hot IC / battery drains</div><div>Disconnect power immediately. Look for +9 V-to-ground shorts, a backwards IC, or a reversed electrolytic. Do not continue until corrected.</div><div class="issue">Squeal or distortion</div><div>Confirm the 10 Ω + 47 nF Zobel is series-connected from pin 5 to ground. Shorten output leads and ensure pin 7 bypass capacitors are correctly oriented.</div></div></section><footer class="footer">LM386 DIP-8 reference: 1 gain · 2 GND · 3 input+ · 4 GND · 5 output · 6 VCC · 7 bypass · 8 gain. Values are practical starting points; check your specific LM386 datasheet before a permanent build.</footer>`;
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