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<header class="hero">
<div class="hero-inner">
<span class="tag">Project Guide · Analog Audio · Beginner-Friendly</span>
<h1>Build a <span class="accent">Stereo Audio Amplifier</span><br>on a Breadboard — LM386 ×2</h1>
<p class="sub">A complete, engineer-reviewed walkthrough for building a two-channel (stereo) audio power
amplifier using the classic LM386 IC — no soldering required. Drive a pair of 8 Ω speakers from your
phone, laptop, or MP3 player, powered by a single 9 V battery.</p>
<div class="meta">
<span>⏱ <b>Build time:</b> 60–90 min</span>
<span>⚡ <b>Power:</b> 9 V DC (battery-safe)</span>
<span>🔊 <b>Output:</b> ~0.5 W / channel into 8 Ω</span>
<span>🎚 <b>Difficulty:</b> Beginner+</span>
</div>
</div>
</header>
<nav class="toc">
<ul>
<li><a href="#intro">01·Intro</a></li>
<li><a href="#safety">02·Safety & Tools</a></li>
<li><a href="#parts">03·Parts List</a></li>
<li><a href="#schematic">04·Circuit Diagrams</a></li>
<li><a href="#assembly">05·Assembly</a></li>
<li><a href="#testing">06·Testing & Troubleshooting</a></li>
</ul>
</nav>
<main>
<!-- ================= 1. INTRO ================= -->
<section id="intro">
<h2><span class="num">01</span> Introduction — How This Amplifier Works</h2>
<p class="lead">An audio amplifier takes a small, weak signal — like the headphone output of your phone,
typically less than one volt and only a few milliwatts — and boosts it to a level strong enough to move a
speaker cone and fill a room with sound. In this project you will build <strong>two identical amplifier
channels</strong> (left and right) to create a true stereo system.</p>
<h3>The star of the show: the LM386</h3>
<p>The <strong>LM386 Low Voltage Audio Power Amplifier</strong> is a legendary 8-pin IC that has been in
production since the 1970s. It contains an entire power amplifier stage on a single chip: a differential
input, gain-setting network, and a class-AB output stage capable of driving an 8 Ω speaker directly.
It runs happily from 4–12 V, needs only a handful of external parts, and is nearly indestructible —
which makes it perfect for a first analog build.</p>
<div class="grid">
<div class="card">
<h4>⚙ Signal Path</h4>
<p>Audio source → volume potentiometer → input coupling capacitor → LM386 (gain ×20) →
output coupling capacitor → speaker. Each stereo channel gets its own identical path.</p>
</div>
<div class="card">
<h4>📈 Gain</h4>
<p>Out of the box, the LM386 has a fixed voltage gain of <strong>20 (26 dB)</strong>. Adding a 10 µF
capacitor between pins 1 and 8 raises it to <strong>200 (46 dB)</strong> — we build at ×20 for clean sound,
and show you the optional gain-boost mod.</p>
</div>
<div class="card">
<h4>🔊 Why "stereo" = two amps</h4>
<p>Stereo audio carries two independent signals (L and R). Rather than one complicated chip, we simply
duplicate one well-understood amplifier circuit — a real engineering pattern used in commercial gear.</p>
</div>
<div class="card">
<h4>🎯 What you'll achieve</h4>
<p>A working battery-powered stereo amplifier (~0.5 W per channel), plus hands-on understanding of coupling
capacitors, decoupling, grounding, and gain — the core vocabulary of analog electronics.</p>
</div>
</div>
<div class="callout">
<div class="co-title">Key concept — Coupling & decoupling capacitors</div>
<p><strong>Coupling capacitors</strong> (in series with the signal) pass the alternating audio signal while
blocking DC, protecting your speaker and your audio source. <strong>Decoupling (bypass) capacitors</strong>
(from power to ground) act like tiny local batteries, smoothing the supply so the amplifier doesn't hum,
hiss, or oscillate. You'll place both in this build — and you'll hear the difference if you forget them.</p>
</div>
<h3>LM386 pinout — memorize this</h3>
<figure class="diagram">
<svg viewBox="0 0 720 300" role="img" aria-label="LM386 pinout diagram">
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.pinnum{font:700 13px Consolas,monospace;fill:#38d9a9}
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<circle cx="292" cy="72" r="6" fill="#0b0f14" stroke="#3b5068" stroke-width="1.5"/>
<text class="chipname" x="360" y="165" text-anchor="middle">LM386</text>
<text class="pinrole" x="360" y="186" text-anchor="middle">(top view)</text>
<!-- left pins 1-4 -->
<g>
<rect class="pinlead" x="240" y="66" width="30" height="12" rx="2"/>
<text class="pinnum" x="280" y="77">1</text>
<text class="pinlabel" x="228" y="77" text-anchor="end">GAIN</text>
<text class="pinrole" x="228" y="93" text-anchor="end">gain-set (opt.)</text>
<rect class="pinlead" x="240" y="118" width="30" height="12" rx="2"/>
<text class="pinnum" x="280" y="129">2</text>
<text class="pinlabel" x="228" y="129" text-anchor="end">−IN</text>
<text class="pinrole" x="228" y="145" text-anchor="end">→ ground</text>
<rect class="pinlead" x="240" y="170" width="30" height="12" rx="2"/>
<text class="pinnum" x="280" y="181">3</text>
<text class="pinlabel" x="228" y="181" text-anchor="end">+IN</text>
<text class="pinrole" x="228" y="197" text-anchor="end">audio signal in</text>
<rect class="pinlead" x="240" y="222" width="30" height="12" rx="2"/>
<text class="pinnum" x="280" y="233">4</text>
<text class="pinlabel" x="228" y="233" text-anchor="end">GND</text>
<text class="pinrole" x="228" y="249" text-anchor="end">power ground</text>
</g>
<!-- right pins 5-8 -->
<g>
<rect class="pinlead" x="450" y="222" width="30" height="12" rx="2"/>
<text class="pinnum" x="440" y="233" text-anchor="end">5</text>
<text class="pinlabel" x="492" y="233">V<tspan font-size="11" dy="3">OUT</tspan></text>
<text class="pinrole" x="492" y="249">→ speaker (via cap)</text>
<rect class="pinlead" x="450" y="170" width="30" height="12" rx="2"/>
<text class="pinnum" x="440" y="181" text-anchor="end">6</text>
<text class="pinlabel" x="492" y="181">V<tspan font-size="11" dy="3">S</tspan></text>
<text class="pinrole" x="492" y="197">+9 V supply</text>
<rect class="pinlead" x="450" y="118" width="30" height="12" rx="2"/>
<text class="pinnum" x="440" y="129" text-anchor="end">7</text>
<text class="pinlabel" x="492" y="129">BYPASS</text>
<text class="pinrole" x="492" y="145">ripple filter (opt.)</text>
<rect class="pinlead" x="450" y="66" width="30" height="12" rx="2"/>
<text class="pinnum" x="440" y="77" text-anchor="end">8</text>
<text class="pinlabel" x="492" y="77">GAIN</text>
<text class="pinrole" x="492" y="93">gain-set (opt.)</text>
</g>
<!-- notch hint -->
<text class="pinrole" x="360" y="34" text-anchor="middle">notch / dot marks pin 1 end</text>
<line x1="360" y1="40" x2="360" y2="48" stroke="#8aa0b5" stroke-width="1.5" marker-end="none"/>
</svg>
<figcaption>Fig. 1 — LM386 (DIP-8) pinout, viewed from above. The notch or dot always identifies the pin-1 end.</figcaption>
</figure>
</section>
<!-- ================= 2. SAFETY ================= -->
<section id="safety">
<h2><span class="num">02</span> Safety & Prerequisites</h2>
<p>This is a <strong>low-voltage project</strong> — a 9 V battery cannot shock you — but good bench habits
formed now will protect you (and your components) on every future project.</p>
<div class="callout danger">
<div class="co-title">⚠ Non-negotiable rules</div>
<ul class="list">
<li><strong>Never wire the circuit with power connected.</strong> Always disconnect the battery before
adding, moving, or removing any component or jumper.</li>
<li><strong>Respect electrolytic capacitor polarity.</strong> A reversed electrolytic cap can heat up,
vent, or pop. The stripe on the can marks the <em>negative</em> lead; the longer lead is positive.</li>
<li><strong>Use a battery or a current-limited supply — not a wall adapter of unknown quality.</strong>
If you use a bench supply, set the current limit to ≤ 300 mA.</li>
<li><strong>Start at zero volume.</strong> Always power up with the potentiometers fully counter-clockwise
to protect your ears and speakers.</li>
<li>If anything gets <strong>hot to the touch or smells odd — disconnect power immediately</strong> and
recheck the wiring before continuing.</li>
</ul>
</div>
<h3>Tools you'll need</h3>
<div class="grid">
<div class="card">
<h4>🛠 Essential</h4>
<ul>
<li>Solderless breadboard (830-point recommended)</li>
<li>Jumper wire kit (male–male)</li>
<li>Wire cutters / strippers</li>
<li>Digital multimeter (continuity + DC volts)</li>
<li>Audio source with 3.5 mm output (phone, laptop, MP3 player)</li>
</ul>
</div>
<div class="card">
<h4>➕ Nice to have</h4>
<ul>
<li>Needle-nose pliers (bending leads, seating the IC)</li>
<li>Soldering iron — <em>optional</em>; only needed if your 3.5 mm jack or pot needs leads attached</li>
<li>Alligator clip leads (temporary speaker hookup)</li>
<li>Anti-static work mat</li>
</ul>
</div>
</div>
<h3>Knowledge prerequisites</h3>
<ul class="list">
<li><strong>Breadboard anatomy:</strong> the two long side rails run the full length (power & ground);
the short 5-hole rows in the middle are connected horizontally, split by the center trench. ICs straddle the trench.</li>
<li><strong>Resistor color codes</strong> — or just measure each resistor with your multimeter before use.</li>
<li><strong>Reading a schematic:</strong> lines are wires, dots are junctions, and the symbols used here are
introduced in Section 04 with a legend.</li>
<li><strong>Capacitor markings:</strong> ceramic caps like <code class="inline">104</code> = 10 × 10⁴ pF = 100 nF (0.1 µF).
Electrolytics print their value and voltage directly on the can.</li>
</ul>
<div class="callout warn">
<div class="co-title">Hearing safety</div>
<p>0.5 W into an efficient speaker at close range is genuinely loud. Test at low volume, keep speakers facing
away from your ears, and never wear headphones plugged into a circuit under test.</p>
</div>
</section>
<!-- ================= 3. PARTS ================= -->
<section id="parts">
<h2><span class="num">03</span> Complete Parts List (Bill of Materials)</h2>
<p>Everything below is common and inexpensive — total cost is typically <strong>under $15</strong> excluding
tools. Quantities shown build <strong>both</strong> stereo channels.</p>
<div class="table-wrap">
<table>
<thead>
<tr><th>Ref</th><th>Component / Part Number</th><th>Qty</th><th>Purpose / Role in Circuit</th></tr>
</thead>
<tbody>
<tr>
<td class="mono">U1, U2</td>
<td><span class="pn">LM386N-1</span><span class="sm">Low Voltage Audio Power Amplifier IC, DIP-8</span></td>
<td class="qty">2</td>
<td>The amplifier itself — one IC per stereo channel. Gain ×20 default.</td>
</tr>
<tr>
<td class="mono">C1, C2</td>
<td><span class="pn">10 µF electrolytic, ≥16 V</span><span class="sm">radial, polarized</span></td>
<td class="qty">2</td>
<td>Input coupling — blocks DC from the source, passes audio into pin 3.</td>
</tr>
<tr>
<td class="mono">C3, C4</td>
<td><span class="pn">220 µF electrolytic, ≥16 V</span><span class="sm">radial, polarized</span></td>
<td class="qty">2</td>
<td>Output coupling — blocks the ~4.5 V DC offset at pin 5 so only audio reaches the speaker.</td>
</tr>
<tr>
<td class="mono">C5, C6</td>
<td><span class="pn">100 nF (0.1 µF) ceramic</span><span class="sm">marked "104"</span></td>
<td class="qty">2</td>
<td>Power decoupling — one per IC, placed close to pin 6, kills supply noise and oscillation.</td>
</tr>
<tr>
<td class="mono">C7</td>
<td><span class="pn">220 µF electrolytic, ≥16 V</span></td>
<td class="qty">1</td>
<td>Bulk supply reservoir across the power rails — steadies the battery under load.</td>
</tr>
<tr>
<td class="mono">C8, C9</td>
<td><span class="pn">10 µF electrolytic, ≥16 V</span><span class="sm">optional</span></td>
<td class="qty">2</td>
<td><em>Optional:</em> pin 7 bypass caps — further reduce hum/ripple from a weak battery.</td>
</tr>
<tr>
<td class="mono">R1, R2</td>
<td><span class="pn">10 Ω, ¼ W resistor</span><span class="sm">brown-black-black-gold</span></td>
<td class="qty">2</td>
<td>Zobel network resistor — with C10/C11, stabilizes the output against RF oscillation.</td>
</tr>
<tr>
<td class="mono">C10, C11</td>
<td><span class="pn">47 nF ceramic</span><span class="sm">marked "473"</span></td>
<td class="qty">2</td>
<td>Zobel network capacitor — in series with R1/R2 from pin 5 to ground.</td>
</tr>
<tr>
<td class="mono">VR1, VR2</td>
<td><span class="pn">10 kΩ potentiometer</span><span class="sm">logarithmic (audio) taper preferred; breadboard-friendly or with leads</span></td>
<td class="qty">2</td>
<td>Volume control — one per channel, forms an adjustable voltage divider on the input.</td>
</tr>
<tr>
<td class="mono">J1</td>
<td><span class="pn">3.5 mm stereo audio jack</span><span class="sm">breadboard-friendly breakout, or jack + 3 leads</span></td>
<td class="qty">1</td>
<td>Audio input from phone/laptop. Tip = Left, Ring = Right, Sleeve = Ground.</td>
</tr>
<tr>
<td class="mono">SPK1, SPK2</td>
<td><span class="pn">8 Ω speaker, 0.5–3 W</span><span class="sm">50–77 mm diameter works well</span></td>
<td class="qty">2</td>
<td>Output transducers — one per channel.</td>
</tr>
<tr>
<td class="mono">BT1</td>
<td><span class="pn">9 V battery + snap connector</span><span class="sm">or 9 V / 500 mA bench supply</span></td>
<td class="qty">1</td>
<td>Power source for both channels.</td>
</tr>
<tr>
<td class="mono">SW1</td>
<td><span class="pn">SPST slide/toggle switch</span><span class="sm">optional but recommended</span></td>
<td class="qty">1</td>
<td>Power on/off — beats yanking the battery snap every time.</td>
</tr>
<tr>
<td class="mono">—</td>
<td><span class="pn">830-point solderless breadboard</span></td>
<td class="qty">1</td>
<td>Build platform. Both channels fit comfortably on one full-size board.</td>
</tr>
<tr>
<td class="mono">—</td>
<td><span class="pn">Jumper wires, male–male</span><span class="sm">assorted lengths & colors</span></td>
<td class="qty">~25</td>
<td>All interconnections. Use <strong>red = +9 V, black = GND</strong>, other colors for signal.</td>
</tr>
</tbody>
</table>
</div>
<div class="callout">
<div class="co-title">Buying tips</div>
<p>Get the <strong>LM386N-1</strong> (through-hole DIP-8), not the surface-mount LM386M. For potentiometers,
a <em>logarithmic (audio, "A10K") taper</em> feels natural for volume; a linear ("B10K") pot works fine too.
If your pot's pins are too fat for the breadboard, solder or clip three short jumper wires to its terminals.</p>
</div>
</section>
<!-- ================= 4. DIAGRAMS ================= -->
<section id="schematic">
<h2><span class="num">04</span> Circuit Diagrams</h2>
<p>The stereo amplifier is simply <strong>two identical copies</strong> of the single-channel circuit below —
one for Left, one for Right — sharing the same battery and ground. Study the schematic first, then use the
breadboard view and the connection checklist to place every wire.</p>
<h3>4.1 — Schematic (one channel)</h3>
<figure class="diagram">
<svg viewBox="0 0 920 545" role="img" aria-label="LM386 single channel schematic">
<defs>
<style>
.w{stroke:#d7e1ec;stroke-width:2;fill:none;stroke-linecap:round}
.wd{stroke:#8aa0b5;stroke-width:2;fill:none;stroke-dasharray:5 5;stroke-linecap:round}
.cs{stroke:#38d9a9;stroke-width:2.4;fill:none;stroke-linecap:round}
.csd{stroke:#38d9a9;stroke-width:2.4;fill:none;stroke-dasharray:5 5;stroke-linecap:round}
.amp{stroke:#4dabf7;stroke-width:2.5;fill:rgba(77,171,247,.06)}
.lb{font:600 14px Consolas,monospace;fill:#38d9a9}
.lb2{font:12px Consolas,monospace;fill:#8aa0b5}
.pn2{font:700 13px Consolas,monospace;fill:#4dabf7}
.rail{font:700 15px Consolas,monospace;fill:#ffb454}
.ttl{font:700 16px Consolas,monospace;fill:#d7e1ec}
.jdot{fill:#d7e1ec}
</style>
</defs>
<text class="ttl" x="30" y="30">One LM386 channel — build this twice (Left & Right)</text>
<!-- +9V rail (segments, gap for switch) -->
<line class="w" x1="140" y1="70" x2="825" y2="70"/>
<line class="w" x1="850" y1="70" x2="870" y2="70"/>
<text class="rail" x="132" y="75" text-anchor="end">+9 V</text>
<!-- switch SW1 -->
<line class="cs" x1="850" y1="70" x2="828" y2="55"/>
<circle cx="825" cy="70" r="3" fill="#38d9a9"/>
<circle cx="850" cy="70" r="3" fill="#38d9a9"/>
<text class="lb" x="838" y="42" text-anchor="middle">SW1</text>
<!-- GND rail -->
<line class="w" x1="100" y1="470" x2="870" y2="470"/>
<!-- ground symbol -->
<line class="w" x1="100" y1="470" x2="100" y2="482"/>
<line class="w" x1="86" y1="482" x2="114" y2="482"/>
<line class="w" x1="92" y1="489" x2="108" y2="489"/>
<line class="w" x1="97" y1="496" x2="103" y2="496"/>
<text class="lb2" x="100" y="514" text-anchor="middle">GND (0 V)</text>
<!-- battery -->
<line class="w" x1="870" y1="70" x2="870" y2="252"/>
<line class="cs" x1="848" y1="255" x2="892" y2="255"/>
<line class="cs" x1="858" y1="271" x2="882" y2="271" stroke-width="5"/>
<line class="w" x1="870" y1="273" x2="870" y2="470"/>
<text class="lb" x="900" y="252" text-anchor="start">+</text>
<text class="lb" x="900" y="272">BT1</text>
<text class="lb2" x="900" y="288">9 V</text>
<!-- C7 bulk cap 220u -->
<line class="w" x1="800" y1="70" x2="800" y2="256"/>
<line class="cs" x1="786" y1="258" x2="814" y2="258"/>
<path class="cs" d="M786 276 Q800 266 814 276"/>
<line class="w" x1="800" y1="274" x2="800" y2="470"/>
<text class="lb" x="778" y="248" text-anchor="end">C7</text>
<text class="lb2" x="778" y="263" text-anchor="end">220µF</text>
<text class="lb2" x="818" y="252">+</text>
<!-- C5 decoupling 100n -->
<line class="w" x1="740" y1="70" x2="740" y2="256"/>
<line class="cs" x1="726" y1="258" x2="754" y2="258"/>
<line class="cs" x1="726" y1="268" x2="754" y2="268"/>
<line class="w" x1="740" y1="270" x2="740" y2="470"/>
<text class="lb" x="718" y="248" text-anchor="end">C5</text>
<text class="lb2" x="718" y="263" text-anchor="end">0.1µF</text>
<!-- input jack -->
<circle class="cs" cx="75" cy="165" r="7"/>
<circle cx="75" cy="165" r="2.5" fill="#38d9a9"/>
<text class="lb2" x="40" y="140">audio in (L)</text>
<text class="lb2" x="40" y="154">jack tip</text>
<line class="w" x1="82" y1="165" x2="180" y2="165"/>
<!-- potentiometer VR1 -->
<line class="w" x1="180" y1="165" x2="180" y2="175"/>
<path class="cs" d="M180 175 l8 6 l-16 12 l16 12 l-16 12 l16 12 l-16 12 l8 6"/>
<line class="w" x1="180" y1="247" x2="180" y2="470"/>
<!-- wiper -->
<line class="cs" x1="215" y1="211" x2="196" y2="211"/>
<path d="M196 211 l9 -5 v10 z" fill="#38d9a9"/>
<line class="w" x1="215" y1="211" x2="246" y2="211"/>
<text class="lb" x="166" y="200" text-anchor="end">VR1</text>
<text class="lb2" x="166" y="215" text-anchor="end">10k</text>
<text class="lb2" x="166" y="230" text-anchor="end">volume</text>
<!-- C1 input coupling -->
<path class="cs" d="M248 197 Q258 211 248 225"/>
<line class="cs" x1="260" y1="197" x2="260" y2="225"/>
<line class="w" x1="260" y1="211" x2="390" y2="211"/>
<text class="lb" x="255" y="185" text-anchor="middle">C1 10µF</text>
<text class="lb2" x="270" y="240">+ toward pin 3</text>
<!-- amp triangle -->
<path class="amp" d="M390 175 L390 315 L540 245 Z"/>
<text class="pn2" x="404" y="218" font-size="17">+</text>
<text class="pn2" x="404" y="286" font-size="17">−</text>
<text class="lb" x="452" y="252" text-anchor="middle" fill="#4dabf7">LM386</text>
<text class="pn2" x="377" y="205" text-anchor="end">3</text>
<text class="pn2" x="377" y="272" text-anchor="end">2</text>
<!-- pin2 to gnd -->
<line class="w" x1="390" y1="277" x2="350" y2="277"/>
<line class="w" x1="350" y1="277" x2="350" y2="470"/>
<!-- pin 6 up / pin 4 down -->
<line class="w" x1="455" y1="205" x2="455" y2="70"/>
<text class="pn2" x="464" y="190">6</text>
<line class="w" x1="455" y1="285" x2="455" y2="470"/>
<text class="pn2" x="464" y="308">4</text>
<!-- pin 7 optional bypass -->
<line class="wd" x1="505" y1="262" x2="505" y2="342"/>
<line class="csd" x1="491" y1="345" x2="519" y2="345"/>
<path class="csd" d="M491 362 Q505 352 519 362"/>
<line class="wd" x1="505" y1="360" x2="505" y2="470"/>
<text class="pn2" x="513" y="276">7</text>
<text class="lb2" x="513" y="392">C8 10µF</text>
<text class="lb2" x="513" y="406">(optional)</text>
<!-- output node & wire -->
<line class="w" x1="540" y1="245" x2="645" y2="245"/>
<circle class="jdot" cx="580" cy="245" r="4"/>
<text class="pn2" x="548" y="234">5</text>
<!-- Zobel: R1 + C10 -->
<line class="w" x1="580" y1="245" x2="580" y2="260"/>
<path class="cs" d="M580 260 l6 5 l-12 9 l12 9 l-12 9 l12 9 l-12 9 l6 5"/>
<line class="w" x1="580" y1="315" x2="580" y2="343"/>
<line class="cs" x1="566" y1="345" x2="594" y2="345"/>
<line class="cs" x1="566" y1="355" x2="594" y2="355"/>
<line class="w" x1="580" y1="357" x2="580" y2="470"/>
<text class="lb" x="596" y="288">R1 10Ω</text>
<text class="lb" x="600" y="340">C10 47nF</text>
<text class="lb2" x="600" y="356">(Zobel)</text>
<!-- C3 output coupling -->
<line class="cs" x1="648" y1="231" x2="648" y2="259"/>
<path class="cs" d="M660 231 Q650 245 660 259"/>
<line class="w" x1="660" y1="245" x2="690" y2="245"/>
<text class="lb" x="653" y="218" text-anchor="middle">C3 220µF</text>
<text class="lb2" x="636" y="275" text-anchor="end">+</text>
<!-- speaker -->
<path class="w" d="M690 245 L690 240 L710 240"/>
<rect class="cs" x="710" y="228" width="16" height="34" rx="2"/>
<path class="cs" d="M726 230 L746 213 L746 277 L726 260 Z"/>
<path class="w" d="M710 252 L700 252 L700 470"/>
<text class="lb" x="736" y="298" text-anchor="middle">SPK1 8Ω</text>
<!-- junction dots -->
<circle class="jdot" cx="455" cy="70" r="4"/>
<circle class="jdot" cx="740" cy="70" r="4"/>
<circle class="jdot" cx="800" cy="70" r="4"/>
<circle class="jdot" cx="180" cy="470" r="4"/>
<circle class="jdot" cx="350" cy="470" r="4"/>
<circle class="jdot" cx="455" cy="470" r="4"/>
<circle class="jdot" cx="505" cy="470" r="4"/>
<circle class="jdot" cx="580" cy="470" r="4"/>
<circle class="jdot" cx="700" cy="470" r="4"/>
<circle class="jdot" cx="740" cy="470" r="4"/>
<circle class="jdot" cx="800" cy="470" r="4"/>
<text class="lb2" x="460" y="532" text-anchor="middle">Pins 1 & 8 left unconnected → gain = 20 (26 dB). Optional: add 10 µF between pin 1 (+) and pin 8 for gain = 200.</text>
</svg>
<figcaption>Fig. 2 — Single-channel LM386 amplifier schematic. Duplicate for the second (Right) channel; both channels share BT1, SW1, C7 and the ground rail.</figcaption>
</figure>
<figure class="diagram">
<svg viewBox="0 0 920 110" role="img" aria-label="Schematic symbol legend">
<defs>
<style>
.cs2{stroke:#38d9a9;stroke-width:2.2;fill:none;stroke-linecap:round}
.w2{stroke:#d7e1ec;stroke-width:2;fill:none}
.lg{font:12px Consolas,monospace;fill:#8aa0b5}
</style>
</defs>
<text class="lg" x="20" y="28" font-weight="700" fill="#d7e1ec">LEGEND</text>
<!-- resistor -->
<path class="cs2" d="M20 60 h8 l4 -8 l6 16 l6 -16 l6 16 l6 -16 l4 8 h8"/>
<text class="lg" x="49" y="90" text-anchor="middle">resistor</text>
<!-- ceramic cap -->
<line class="w2" x1="150" y1="60" x2="168" y2="60"/>
<line class="cs2" x1="168" y1="48" x2="168" y2="72"/>
<line class="cs2" x1="178" y1="48" x2="178" y2="72"/>
<line class="w2" x1="178" y1="60" x2="196" y2="60"/>
<text class="lg" x="173" y="90" text-anchor="middle">ceramic cap</text>
<!-- polarized cap -->
<line class="w2" x1="290" y1="60" x2="308" y2="60"/>
<line class="cs2" x1="308" y1="48" x2="308" y2="72"/>
<path class="cs2" d="M322 48 Q312 60 322 72"/>
<line class="w2" x1="318" y1="60" x2="336" y2="60"/>
<text class="lg" x="300" y="44">+</text>
<text class="lg" x="313" y="90" text-anchor="middle">electrolytic (+/−)</text>
<!-- potentiometer -->
<path class="cs2" d="M430 40 l5 4 l-10 7 l10 7 l-10 7 l10 7 l-5 4"/>
<line class="cs2" x1="452" y1="58" x2="440" y2="58"/>
<path d="M440 58 l8 -4.5 v9 z" fill="#38d9a9"/>
<text class="lg" x="440" y="90" text-anchor="middle">potentiometer</text>
<!-- speaker -->
<rect class="cs2" x="540" y="48" width="10" height="24" rx="2"/>
<path class="cs2" d="M550 50 L564 38 L564 82 L550 70 Z"/>
<text class="lg" x="556" y="98" text-anchor="middle">speaker</text>
<!-- ground -->
<line class="w2" x1="660" y1="42" x2="660" y2="58"/>
<line class="w2" x1="646" y1="58" x2="674" y2="58"/>
<line class="w2" x1="652" y1="65" x2="668" y2="65"/>
<line class="w2" x1="657" y1="72" x2="663" y2="72"/>
<text class="lg" x="660" y="90" text-anchor="middle">ground</text>
<!-- junction -->
<line class="w2" x1="750" y1="60" x2="790" y2="60"/>
<line class="w2" x1="770" y1="42" x2="770" y2="78"/>
<circle cx="770" cy="60" r="4" fill="#d7e1ec"/>
<text class="lg" x="770" y="96" text-anchor="middle">junction</text>
<!-- dashed optional -->
<line x1="840" y1="60" x2="890" y2="60" stroke="#8aa0b5" stroke-width="2" stroke-dasharray="5 5"/>
<text class="lg" x="865" y="90" text-anchor="middle">optional</text>
</svg>
<figcaption>Fig. 3 — Symbol legend for the schematic above.</figcaption>
</figure>
<h3>4.2 — Breadboard wiring guide (full stereo build)</h3>
<p>The view below shows the complete stereo layout on one 830-point breadboard. <strong>U1 (columns 12–15)
is the Left channel; U2 (columns 38–41) is the Right channel.</strong> Both ICs straddle the center trench
with their notches facing left. Wire colors follow the legend at the bottom of the figure.</p>
<figure class="diagram">
<svg viewBox="0 0 960 570" role="img" aria-label="Breadboard wiring diagram for stereo LM386 amplifier">
<defs>
<pattern id="holes" width="14" height="14" patternUnits="userSpaceOnUse" x="-3" y="1">
<circle cx="7" cy="7" r="2.1" fill="#39424e"/>
</pattern>
<style>
.bw{fill:none;stroke-linecap:round;stroke-width:3}
.wr{stroke:#e8453c}.wk{stroke:#20262e}.wy{stroke:#f5c22b}.wo{stroke:#f28c28}.wg{stroke:#2fb36a}
.bl{font:600 11px Consolas,monospace;fill:#33404e}
.bl2{font:600 11px Consolas,monospace;fill:#8aa0b5}
.rowl{font:700 10px Consolas,monospace;fill:#6b7a89}
.icl{font:700 12px Consolas,monospace;fill:#e9eef4}
.pinno{font:700 9px Consolas,monospace;fill:#33404e}
</style>
</defs>
<!-- speakers -->
<g>
<circle cx="330" cy="36" r="23" fill="#1a222c" stroke="#4a5a6b" stroke-width="2"/>
<circle cx="330" cy="36" r="14" fill="none" stroke="#4a5a6b" stroke-width="1.5"/>
<circle cx="330" cy="36" r="5" fill="#4a5a6b"/>
<text class="bl2" x="296" y="18" text-anchor="end">SPK1 (L) 8Ω</text>
<circle cx="690" cy="36" r="23" fill="#1a222c" stroke="#4a5a6b" stroke-width="2"/>
<circle cx="690" cy="36" r="14" fill="none" stroke="#4a5a6b" stroke-width="1.5"/>
<circle cx="690" cy="36" r="5" fill="#4a5a6b"/>
<text class="bl2" x="722" y="18">SPK2 (R) 8Ω</text>
</g>
<!-- board -->
<rect x="30" y="70" width="912" height="302" rx="8" fill="#cdd5dd" stroke="#98a5b2" stroke-width="2"/>
<!-- rail stripes -->
<line x1="55" y1="83" x2="895" y2="83" stroke="#e03131" stroke-width="3"/>
<line x1="55" y1="115" x2="895" y2="115" stroke="#2f6fd0" stroke-width="3"/>
<line x1="55" y1="322" x2="895" y2="322" stroke="#2f6fd0" stroke-width="3"/>
<line x1="55" y1="353" x2="895" y2="353" stroke="#e03131" stroke-width="3"/>
<!-- trench -->
<rect x="34" y="216" width="904" height="20" fill="#b5bfc9"/>
<line x1="34" y1="216" x2="938" y2="216" stroke="#98a5b2" stroke-width="1.5"/>
<line x1="34" y1="236" x2="938" y2="236" stroke="#98a5b2" stroke-width="1.5"/>
<!-- holes -->
<rect x="53" y="85" width="840" height="28" fill="url(#holes)"/>
<rect x="53" y="141" width="840" height="70" fill="url(#holes)"/>
<rect x="53" y="239" width="840" height="70" fill="url(#holes)"/>
<rect x="53" y="323" width="840" height="28" fill="url(#holes)"/>
<!-- rail signs -->
<g font-family="Consolas,monospace" font-size="13" font-weight="700">
<text x="44" y="96" fill="#e03131">+</text>
<text x="44" y="111" fill="#2f6fd0">−</text>
<text x="44" y="335" fill="#2f6fd0">−</text>
<text x="44" y="349" fill="#e03131">+</text>
</g>
<!-- row letters -->
<text class="rowl" x="907" y="152">a</text><text class="rowl" x="907" y="166">b</text>
<text class="rowl" x="907" y="180">c</text><text class="rowl" x="907" y="194">d</text>
<text class="rowl" x="907" y="208">e</text>
<text class="rowl" x="907" y="250">f</text><text class="rowl" x="907" y="264">g</text>
<text class="rowl" x="907" y="278">h</text><text class="rowl" x="907" y="292">i</text>
<text class="rowl" x="907" y="306">j</text>
<!-- ============ LEFT CHANNEL (U1) ============ -->
<!-- U1 body cols12-15 -->
<rect x="206" y="198" width="58" height="56" rx="4" fill="#171c23" stroke="#000"/>
<path d="M206 218 a9 9 0 0 1 0 16" fill="#cdd5dd"/>
<text class="icl" x="238" y="222" text-anchor="middle">LM386</text>
<text class="icl" x="238" y="237" text-anchor="middle" fill="#38d9a9">U1·L</text>
<text class="pinno" x="214" y="266" text-anchor="middle">1</text>
<text class="pinno" x="228" y="266" text-anchor="middle">2</text>
<text class="pinno" x="242" y="266" text-anchor="middle">3</text>
<text class="pinno" x="256" y="266" text-anchor="middle">4</text>
<text class="pinno" x="256" y="193" text-anchor="middle">5</text>
<text class="pinno" x="242" y="193" text-anchor="middle">6</text>
<text class="pinno" x="228" y="193" text-anchor="middle">7</text>
<text class="pinno" x="214" y="193" text-anchor="middle">8</text>
<!-- W1: +9V to pin6 -->
<path class="bw wr" d="M228 92 C 224 120, 232 134, 242 148"/>
<!-- C5 100nF pin6 col -> top − rail -->
<line x1="242" y1="106" x2="242" y2="162" stroke="#5c554b" stroke-width="2"/>
<circle cx="242" cy="131" r="8" fill="#e8a33d" stroke="#a9752c" stroke-width="1.5"/>
<text class="bl" x="230" y="135" text-anchor="end">C5</text>
<!-- C3 220u out cap rowB cols15->19 -->
<line x1="256" y1="162" x2="312" y2="162" stroke="#5c554b" stroke-width="2"/>
<circle cx="284" cy="162" r="11" fill="#2e3a48" stroke="#101418" stroke-width="1.5"/>
<text x="284" y="166" text-anchor="middle" font-size="10" fill="#d7e1ec" font-weight="700">C3</text>
<text class="bl" x="262" y="152" text-anchor="end">+</text>
<!-- R1 zobel rowC cols15->17 -->
<line x1="256" y1="176" x2="284" y2="176" stroke="#5c554b" stroke-width="2"/>
<rect x="261" y="171" width="18" height="10" rx="4" fill="#d9c79e" stroke="#9c8757"/>
<line x1="265" y1="171" x2="265" y2="181" stroke="#8d5524" stroke-width="2"/>
<line x1="270" y1="171" x2="270" y2="181" stroke="#20262e" stroke-width="2"/>
<text class="bl" x="270" y="193" text-anchor="middle">R1</text>
<!-- C10 zobel cap col17 rowA -> top − rail -->
<line x1="284" y1="106" x2="284" y2="148" stroke="#5c554b" stroke-width="2"/>
<circle cx="284" cy="125" r="8" fill="#e8a33d" stroke="#a9752c" stroke-width="1.5"/>
<text class="bl" x="297" y="129">C10</text>
<!-- speaker L wires -->
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<!-- pin2 & pin4 grounds -->
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<path class="bw wk" d="M256 302 L 256 330"/>
<!-- C1 input cap rowH cols9->14 -->
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<text x="207" y="278" text-anchor="middle" font-size="10" fill="#d7e1ec" font-weight="700">C1</text>
<text class="bl" x="232" y="268" text-anchor="middle">+</text>
<!-- ============ RIGHT CHANNEL (U2) ============ -->
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<text class="icl" x="602" y="222" text-anchor="middle">LM386</text>
<text class="icl" x="602" y="237" text-anchor="middle" fill="#4dabf7">U2·R</text>
<text class="pinno" x="578" y="266" text-anchor="middle">1</text>
<text class="pinno" x="592" y="266" text-anchor="middle">2</text>
<text class="pinno" x="606" y="266" text-anchor="middle">3</text>
<text class="pinno" x="620" y="266" text-anchor="middle">4</text>
<text class="pinno" x="620" y="193" text-anchor="middle">5</text>
<text class="pinno" x="606" y="193" text-anchor="middle">6</text>
<text class="pinno" x="592" y="193" text-anchor="middle">7</text>
<text class="pinno" x="578" y="193" text-anchor="middle">8</text>
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<circle cx="606" cy="131" r="8" fill="#e8a33d" stroke="#a9752c" stroke-width="1.5"/>
<text class="bl" x="594" y="135" text-anchor="end">C6</text>
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<circle cx="648" cy="162" r="11" fill="#2e3a48" stroke="#101418" stroke-width="1.5"/>
<text x="648" y="166" text-anchor="middle" font-size="10" fill="#d7e1ec" font-weight="700">C4</text>
<text class="bl" x="626" y="152" text-anchor="end">+</text>
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<text class="bl" x="634" y="193" text-anchor="middle">R2</text>
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<circle cx="648" cy="125" r="8" fill="#e8a33d" stroke="#a9752c" stroke-width="1.5"/>
<text class="bl" x="661" y="129">C11</text>
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<path class="bw wk" d="M700 52 C 706 68, 704 86, 704 106"/>
<path class="bw wk" d="M592 302 L 592 330"/>
<path class="bw wk" d="M620 302 L 620 330"/>
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<text x="571" y="278" text-anchor="middle" font-size="10" fill="#d7e1ec" font-weight="700">C2</text>
<text class="bl" x="596" y="268" text-anchor="middle">+</text>
<!-- ============ POWER SECTION ============ -->
<!-- C7 bulk cap on bottom rails -->
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<text x="824" y="400" text-anchor="middle" font-size="10" fill="#d7e1ec" font-weight="700">C7</text>
<text class="bl2" x="843" y="400">220µF · + to red rail</text>
<!-- rail bridges -->
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<text class="bl2" x="940" y="225" text-anchor="middle" transform="rotate(90 940 225)">rail bridges</text>
<!-- switch + battery -->
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<rect x="769" y="428" width="16" height="14" rx="3" fill="#38d9a9"/>
<text class="bl2" x="768" y="464" text-anchor="middle">SW1 power</text>
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<text x="891" y="444" text-anchor="middle" font-size="12" fill="#d7e1ec" font-weight="700" font-family="Consolas,monospace">9V</text>
<text x="891" y="460" text-anchor="middle" font-size="10" fill="#8aa0b5" font-family="Consolas,monospace">BT1</text>
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<path class="bw wr" d="M742 435 C 716 434, 800 400, 802 344"/>
<path class="bw wk" d="M888 424 C 884 396, 868 360, 858 330"/>
<!-- ============ INPUT SECTION ============ -->
<!-- jack -->
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<text x="58" y="530" text-anchor="middle" font-size="11" fill="#8aa0b5" font-family="Consolas,monospace">J1 · 3.5mm</text>
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<circle cx="78" cy="486" r="3" fill="#20262e" stroke="#8aa0b5"/>
<text class="bl2" x="86" y="460">tip·L</text>
<text class="bl2" x="86" y="475">ring·R</text>
<text class="bl2" x="86" y="490">slv·GND</text>
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<!-- VR1 -->
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<circle cx="160" cy="478" r="9" fill="#38424e"/>
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<text x="160" y="530" text-anchor="middle" font-size="11" fill="#8aa0b5" font-family="Consolas,monospace">VR1 · vol L</text>
<circle cx="145" cy="452" r="3" fill="#f5c22b"/>
<circle cx="160" cy="450" r="3" fill="#f5c22b"/>
<circle cx="175" cy="452" r="3" fill="#20262e" stroke="#8aa0b5"/>
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<path class="bw wy" d="M160 450 C 164 400, 168 330, 172 288"/>
<path class="bw wk" d="M175 452 C 186 420, 168 360, 144 330"/>
<!-- VR2 -->
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<circle cx="480" cy="478" r="9" fill="#38424e"/>
<line x1="480" y1="478" x2="480" y2="461" stroke="#d7e1ec" stroke-width="2.5"/>
<text x="480" y="530" text-anchor="middle" font-size="11" fill="#8aa0b5" font-family="Consolas,monospace">VR2 · vol R</text>
<circle cx="465" cy="452" r="3" fill="#f28c28"/>
<circle cx="480" cy="450" r="3" fill="#f28c28"/>
<circle cx="495" cy="452" r="3" fill="#20262e" stroke="#8aa0b5"/>
<path class="bw wo" d="M78 471 C 200 510, 340 512, 465 452"/>
<path class="bw wo" d="M480 450 C 490 400, 520 340, 536 288"/>
<path class="bw wk" d="M495 452 C 510 420, 512 370, 508 330"/>
<!-- legend -->
<g font-family="Consolas,monospace" font-size="11">
<line class="bw wr" x1="230" y1="551" x2="258" y2="551"/><text class="bl2" x="264" y="555">+9V</text>
<line class="bw wk" x1="304" y1="551" x2="332" y2="551"/><text class="bl2" x="338" y="555">GND</text>
<line class="bw wy" x1="378" y1="551" x2="406" y2="551"/><text class="bl2" x="412" y="555">L signal</text>
<line class="bw wo" x1="474" y1="551" x2="502" y2="551"/><text class="bl2" x="508" y="555">R signal</text>
<line class="bw wg" x1="574" y1="551" x2="602" y2="551"/><text class="bl2" x="608" y="555">speaker out</text>
</g>
</svg>
<figcaption>Fig. 4 — Full stereo breadboard layout. ICs straddle the trench, notch left. Pot & jack connect via flying leads.</figcaption>
</figure>
<h3>4.3 — Pin-to-pin connection map</h3>
<p>Use this as your wiring checklist — every connection in the build, per channel. "Rail" refers to the
breadboard power strips.</p>
<pre class="code"><span class="c">## LEFT CHANNEL — U1 (repeat identically for U2 / Right)</span>
U1 pin 1 (GAIN) → <span class="v">no connection</span> <span class="c"># gain stays ×20</span>
U1 pin 2 (−IN) → <span class="k">GND rail</span> <span class="c"># black jumper</span>
U1 pin 3 (+IN) → <span class="k">C1 (+) lead</span> · C1 (−) → VR1 wiper <span class="c"># 10 µF, + faces pin 3</span>
U1 pin 4 (GND) → <span class="k">GND rail</span> <span class="c"># black jumper</span>
U1 pin 5 (OUT) → <span class="k">C3 (+) lead</span> · C3 (−) → SPK1 (+) <span class="c"># 220 µF, + faces pin 5</span>
→ <span class="k">R1 (10 Ω)</span> → C10 (47 nF) → GND <span class="c"># Zobel network</span>
U1 pin 6 (Vs) → <span class="k">+9 V rail</span> <span class="c"># red jumper</span>
→ <span class="k">C5 (100 nF)</span> → GND <span class="c"># decoupling, close to pin 6</span>
U1 pin 7 (BYPASS) → <span class="v">optional:</span> C8 10 µF (+) → GND
U1 pin 8 (GAIN) → <span class="v">no connection</span>
<span class="c">## INPUT — shared 3.5 mm jack J1</span>
J1 sleeve → GND rail <span class="c"># MUST share ground with everything</span>
J1 tip → VR1 outer terminal <span class="c"># Left audio</span>
J1 ring → VR2 outer terminal <span class="c"># Right audio</span>
VR1/VR2 other outer terminal → GND · wiper (middle) → C1/C2 (−)
<span class="c">## POWER — shared</span>
BT1 (+) → SW1 → +9 V rails (top & bottom bridged)
BT1 (−) → GND rails (top & bottom bridged)
C7 220 µF across rails, (+) to +9 V
SPK1/SPK2 (−) → GND rail</pre>
</section>
<!-- ================= 5. ASSEMBLY ================= -->
<section id="assembly">
<h2><span class="num">05</span> Step-by-Step Assembly</h2>
<p>Work with the <strong>battery disconnected</strong> throughout. Build the Left channel first, test it,
then duplicate for the Right channel — debugging one channel is far easier than debugging two at once.</p>
<ol class="steps">
<li>
<h4>Prepare the breadboard & power rails</h4>
<p>Orient the board with the long rails horizontal. Bridge the top and bottom rail pairs with two jumpers
at the far right: <strong>red jumper</strong> top + to bottom +, <strong>black jumper</strong>
top − to bottom −. Decide now and never deviate: <strong>red stripe = +9 V, blue stripe = GND</strong>.</p>
<span class="step-check">✓ Check: multimeter continuity beeps between the two + rails, and between the two − rails. No beep between + and −.</span>
</li>
<li>
<h4>Seat the two LM386 ICs</h4>
<p>Place <strong>U1 (Left)</strong> straddling the center trench around columns 12–15 and
<strong>U2 (Right)</strong> around columns 38–41, both with the <strong>notch/dot facing left</strong>.
Press down evenly with a fingertip (or rock gently with pliers) until each chip sits flush — bent-under
pins are the #1 rookie failure.</p>
<ul>
<li>Pins 1–4 are on the lower row (left→right), pins 5–8 on the upper row (right→left).</li>
</ul>
<span class="step-check">✓ Check: view each IC from the side — all 8 legs enter holes, none folded underneath.</span>
</li>
<li>
<h4>Wire power & ground to each IC</h4>
<p>For each IC: <strong>red jumper</strong> from pin 6 (<kbd class="pin">Vs</kbd>) column to the
+9 V rail; <strong>black jumpers</strong> from pin 4 (<kbd class="pin">GND</kbd>) and pin 2
(<kbd class="pin">−IN</kbd>) columns to the GND rail. Grounding pin 2 sets the amplifier's reference —
don't skip it.</p>
<span class="step-check">✓ Check: continuity from each pin-6 column to the + rail; pin-4 and pin-2 columns to the − rail.</span>
</li>
<li>
<h4>Add the decoupling & bulk capacitors</h4>
<p>Place a <strong>100 nF ceramic (C5, C6)</strong> from each pin-6 column directly to the GND rail —
keep the leads as short as possible; these caps only work when they're close to the chip. Then add the
<strong>220 µF bulk cap (C7)</strong> straight across the power rails: long lead (+) into the + rail,
striped lead (−) into the GND rail.</p>
<span class="step-check">✓ Check: C7 stripe faces the blue (GND) rail. Ceramics have no polarity — either way is fine.</span>
</li>
<li>
<h4>Install the input coupling capacitors</h4>
<p>For each channel, place a <strong>10 µF electrolytic (C1, C2)</strong> in the row area below the trench:
the <strong>(+) lead into the pin-3 column</strong>, the (−) lead into a free row a few columns to the left.
That free row becomes your "volume in" node for the pot's wiper.</p>
<span class="step-check">✓ Check: cap stripe (−) points AWAY from the IC, toward the incoming signal.</span>
</li>
<li>
<h4>Wire the volume potentiometers</h4>
<p>Each 10 kΩ pot has three terminals. Connect per channel:</p>
<ul>
<li><strong>Outer terminal A</strong> → audio signal from the jack (tip for VR1/Left, ring for VR2/Right).</li>
<li><strong>Outer terminal B</strong> → GND rail.</li>
<li><strong>Wiper (middle)</strong> → the (−) lead of the input cap (C1 or C2).</li>
</ul>
<p>If the pot won't grip the breadboard, attach three short flying leads (solder, or wrap tightly and tape).
Turned toward terminal B = silence; toward terminal A = full volume.</p>
<span class="step-check">✓ Check: with the pot fully counter-clockwise, continuity between wiper and GND.</span>
</li>
<li>
<h4>Connect the 3.5 mm stereo input jack</h4>
<p>Identify the three jack contacts: <strong>tip = Left</strong>, <strong>ring = Right</strong>,
<strong>sleeve = ground</strong>. Wire sleeve → GND rail, tip → VR1 terminal A, ring → VR2 terminal A.
If unsure which lug is which, plug in a cable and beep the lugs against the plug's tip/ring/sleeve with
your multimeter.</p>
<span class="step-check">✓ Check: sleeve lug beeps to the GND rail. Tip and ring do NOT beep to ground (pot at mid-position).</span>
</li>
<li>
<h4>Add the Zobel networks (stability)</h4>
<p>Per channel, from the <strong>pin-5 column</strong>: a <strong>10 Ω resistor (R1/R2)</strong> in series
with a <strong>47 nF ceramic (C10/C11)</strong> down to the GND rail. Use a free row to join the resistor
and capacitor. This tiny RC network stops the LM386 from bursting into ultrasonic oscillation with real
speaker loads.</p>
<span class="step-check">✓ Check: pin-5 → R → C → GND, in that order. Order of R and C doesn't matter electrically, but keep it tidy.</span>
</li>
<li>
<h4>Install the output capacitors & speakers</h4>
<p>Per channel: <strong>220 µF electrolytic (C3/C4)</strong> with the <strong>(+) lead in the pin-5
column</strong> and the (−) lead in a free row. From that free row, run a wire to the speaker's
<strong>+ terminal</strong>; run the speaker's <strong>− terminal</strong> to the GND rail. Alligator clips
are fine for speakers with bare tabs.</p>
<span class="step-check">✓ Check: both output caps have stripe (−) facing the speaker, (+) facing pin 5. Pin 5 idles at ≈ half the supply voltage, so polarity matters.</span>
</li>
<li>
<h4>Wire the power switch & battery snap</h4>
<p>Battery snap <strong>red lead → SW1 terminal 1</strong>; <strong>SW1 terminal 2 → +9 V rail</strong>;
snap <strong>black lead → GND rail</strong>. Leave the switch OFF and the battery unclipped for now.</p>
<span class="step-check">✓ Check: with switch ON (battery still disconnected!), continuity from the snap's red lead to the + rail.</span>
</li>
<li>
<h4>Pre-flight inspection — do not skip</h4>
<ul>
<li>All four electrolytic stripes point the right way (C1/C2 stripe → jack side; C3/C4 stripe → speaker side; C7 stripe → GND rail).</li>
<li>Multimeter on continuity: <strong>+ rail to GND rail must NOT beep.</strong> A beep means a short — find it before powering up.</li>
<li>Both pots fully counter-clockwise (zero volume).</li>
<li>No component lead accidentally bridging two adjacent rows.</li>
</ul>
</li>
<li>
<h4>Power up & first sound</h4>
<p>Clip in the battery, flip SW1 on, and immediately touch each LM386 — they should be
<strong>cool or barely warm</strong>. Measure DC volts: <strong>pin 6 ≈ 9 V</strong>,
<strong>pin 5 ≈ 4.2–4.7 V</strong> (half-supply) on both chips. Plug your audio source into J1, press play,
and slowly raise each volume pot. Stereo sound! 🎉</p>
<span class="step-check">✓ Success criteria: clean audio from both speakers, independent L/R volume, no hiss-free-squeal, cool ICs.</span>
</li>
</ol>
<div class="callout">
<div class="co-title">Optional upgrades</div>
<ul class="list">
<li><strong>More gain (×200):</strong> add a 10 µF cap between pins 1 (+) and 8 of each LM386. Useful for
very quiet sources; expect more hiss.</li>
<li><strong>Quieter supply:</strong> add the pin-7 bypass caps (C8/C9, 10 µF, + to pin 7, − to GND) to
suppress hum from a tired battery.</li>
<li><strong>Bass boost:</strong> a 10 kΩ resistor + 33 nF cap in series between pins 1 and 5 adds a gentle
low-frequency shelf — a classic LM386 datasheet trick.</li>
</ul>
</div>
</section>
<!-- ================= 6. TESTING ================= -->
<section id="testing">
<h2><span class="num">06</span> Testing & Troubleshooting</h2>
<h3>Safe power-up procedure</h3>
<ol class="list">
<li><strong>Cold checks first (no battery):</strong> continuity from + rail to GND rail must be open.
Verify pin 6 → + rail and pin 4 → GND rail on both ICs.</li>
<li><strong>Volume at zero, no audio source connected</strong> for the very first power-up.</li>
<li>Power on and <strong>measure before you listen</strong>: pin 6 ≈ battery voltage; pin 5 ≈ half the
battery voltage. If pin 5 reads near 0 V or near 9 V, power off — something is miswired.</li>
<li>Feel the ICs after 30 seconds. Warm is fine; too-hot-to-touch means a short or reversed part.</li>
<li>Only then connect the source and raise the volume gradually.</li>
</ol>
<div class="table-wrap">
<table>
<thead><tr><th>Measurement point</th><th>Expected (9 V battery)</th><th>If wrong, suspect…</th></tr></thead>
<tbody>
<tr><td>Pin 6 (Vs) to GND</td><td class="mono">8.5 – 9.5 V</td><td>Dead battery, open switch, wrong rail, IC in backwards</td></tr>
<tr><td>Pin 5 (OUT) to GND</td><td class="mono">4.2 – 4.7 V</td><td>Floating pin 4/2, bent-under leg, damaged IC</td></tr>
<tr><td>Pin 4 to GND rail</td><td class="mono">0 V / continuity</td><td>Missing ground jumper</td></tr>
<tr><td>Battery current draw (idle)</td><td class="mono">8 – 20 mA total</td><td>>100 mA idle = short or reversed electrolytic</td></tr>
<tr><td>Across speaker terminals (DC)</td><td class="mono">≈ 0 V</td><td>Leaky/reversed output cap C3/C4</td></tr>
</tbody>
</table>
</div>
<h3>Common problems & fixes</h3>
<details class="trouble" open>
<summary>No sound at all (one or both channels)</summary>
<div class="body">
<p><strong>Trace the signal path backwards:</strong> speaker → C3 → pin 5 → pin 3 → C1 → pot wiper → jack.</p>
<p>• Verify pin 5 sits at ~4.5 V DC — if not, the IC isn't powered or is seated badly.<br>
• Confirm the pot wiper (middle pin) — a very common mistake is wiring the wiper to ground instead of an outer terminal.<br>
• Push the 3.5 mm plug in <em>fully</em>; half-seated plugs give mono or nothing.<br>
• Wiggle each jumper gently — breadboard spring contacts wear out. Replace suspicious wires.</p>
</div>
</details>
<details class="trouble">
<summary>Loud hum or buzz (50/60 Hz)</summary>
<div class="body">
<p>Almost always a <strong>ground problem</strong>. Confirm the jack's sleeve is tied to the same GND rail
as everything else. Check that both rail pairs are bridged. Keep input wires short and away from the power
wiring. If powering from a cheap wall adapter, switch to a battery — many adapters have terrible ripple;
the pin-7 bypass cap (C8/C9) also helps.</p>
</div>
</details>
<details class="trouble">
<summary>Squealing, motorboating ("putt-putt-putt"), or radio-like whistles</summary>
<div class="body">
<p>The amplifier is <strong>oscillating</strong> — classic LM386 behavior when decoupling is missing.<br>
• Verify C5/C6 (100 nF) sit close to pin 6 with short leads.<br>
• Verify the Zobel network (R + 47 nF) is present on pin 5.<br>
• Separate input wiring (pot, jack) from output wiring (speaker) — output signal coupling back into the
input creates a feedback loop.<br>
• Motorboating with a weak battery: replace the battery and make sure bulk cap C7 is installed.</p>
</div>
</details>
<details class="trouble">
<summary>Distorted / crackling sound</summary>
<div class="body">
<p>• Source volume too high — set your phone to ~70% and use the circuit's pots for level.<br>
• Battery sagging under load (measure pin 6 <em>while playing</em>; below ~7 V, replace it).<br>
• A 9 V battery + LM386 is a ~0.5 W amp — asking for more causes clipping. That's a physics limit, not a fault.<br>
• Intermittent crackle: a loose breadboard contact. Re-seat the ICs and jumpers.</p>
</div>
</details>
<details class="trouble">
<summary>IC gets hot / battery drains fast</summary>
<div class="body">
<p><strong>Power off immediately.</strong><br>
• Check for a reversed electrolytic — especially C7 across the rails and C3/C4 on the outputs.<br>
• Check the IC orientation: notch left in this layout. An LM386 inserted backwards puts +9 V on the output pin.<br>
• Look for a stray wire or lead bridging + and GND, or a speaker wire touching the + rail.</p>
</div>
</details>
<details class="trouble">
<summary>Only one channel works / channels swapped</summary>
<div class="body">
<p>• Swap the working channel's input wire to the dead channel's pot — if sound follows the wire, the dead
amp channel is at fault; if not, the jack wiring (tip vs ring) is at fault.<br>
• L/R reversed is harmless: just swap the tip and ring wires at the pots.<br>
• Check the dead channel's pin-2 ground — a floating pin 2 mutes or garbles the output.</p>
</div>
</details>
<details class="trouble">
<summary>Sound is very quiet even at full volume</summary>
<div class="body">
<p>• Input cap C1/C2 reversed or making poor contact.<br>
• Pot wired as a rheostat instead of a divider (outer terminal B must go to GND).<br>
• Quiet source (some phones limit line-out) — add the gain-boost cap between pins 1 and 8 for ×200 gain.</p>
</div>
</details>
<div class="callout warn">
<div class="co-title">Golden debugging rule</div>
<p>Change <strong>one thing at a time</strong>, then re-test. Ninety percent of breadboard faults are:
a wire in the wrong row (off-by-one), a reversed electrolytic, a bent-under IC pin, or a ground that
isn't actually connected. Check those four before suspecting the chip.</p>
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<div class="co-title">Where to go next</div>
<p>Once it sings: try the bass-boost mod, swap in a TDA2822 or PAM8403 module for comparison, transfer the
circuit to perfboard with a soldering iron, or add a TL072 preamp stage in front for microphone-level
signals. You now understand the amplifier block that hides inside almost every piece of audio gear ever made.</p>
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<p>Breadboard Stereo Amplifier Build Guide · <span class="mono">LM386 ×2 · 9 V · Class-AB</span></p>
<p>Educational content — always double-check polarity and datasheets before powering any circuit.</p>
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