Discrete Class D Amplifier DIY Kit

The Discrete Class D Amplifier DIY Kit is a complete, working audio power amplifier you build from fundamental building blocks — with no dedicated amplifier chip anywhere on the board. A 555 timer generates a ~188 kHz carrier, an LM393 comparator turns your audio into pulse-width-modulated pulses, an IR2113 gate driver and a pair of IRLZ44N MOSFETs switch the power, and a simple LC filter reconstructs it all back into clean, amplified sound. Feed it any 3.5 mm audio source, power it from a 12–20 V supply, connect a 4 Ω or 8 Ω speaker, and hear a Class D amplifier whose every stage you can point to. Labelled test points at each node turn the board into a live map of the signal chain — ideal for probing with an oscilloscope. This is an intermediate-level kit combining through-hole (THD) and surface-mount (0805) components — a great project to practise both techniques on a single board. 📚 Prerequisites You'll need some previous knowledge to get the most out of this kit: ► Ohm's Law and basic voltage-divider intuition ► A feel for how capacitors charge and block DC ► Some experience with SMD passives (0805) recommended — the through-hole parts are beginner-friendly ✨ Key Features No Amplifier Chip — Fully Discrete Every stage is built from fundamental parts: a 555 carrier, a comparator, a gate driver and two MOSFETs. You get to see every stage that a commercial amplifier hides inside a single package. 188 kHz PWM Modulator A 555 timer generates the carrier and an LM393 comparator continuously compares your audio against it, turning quiet line-level sound into high-speed pulses whose width follows the music. Bootstrapped High-Side Gate Drive An IR2113 half-bridge driver and a bootstrap capacitor solve the classic high-side MOSFET problem, switching an IRLZ44N half-bridge cleanly with matched dead time — no shoot-through. Automatic Standby A second comparator and a second 555 detect silence and put the output stage to sleep to save power, then wake the amplifier the instant music returns. A Complete Switch-Mode Lab Labelled test points at every node — Audio IN, carrier, PWM, switch node and filtered output — let you watch audio become pulses and be reconstructed again, stage by stage, on an oscilloscope. 🔧 Required Tools Soldering iron — temperature-controlled (320–350 °C) recommended for the mixed SMD and through-hole parts. DC power supply — 12–20 V (ideally current-limited), connected through the barrel jack. Audio source — a phone, laptop or signal generator with a 3.5 mm output. Test speaker — a 4 Ω or 8 Ω speaker you're happy to experiment with. Multimeter — for continuity checks and verifying the 5 V rail and 2.5 V offset. 🔧 Recommended Tools Oscilloscope — turns this project into a full switch-mode lab: watch the 188 kHz carrier, see the pulse width breathe with the music, and observe the half-bridge switching node. Flux, fine tweezers and a magnifier — make the 0805 passives and SOIC ICs far easier to place and inspect. ⚠️ IMPORTANT: Soldering Safety Soldering irons operate at extreme temperatures (often over 300 °C), posing a severe burn risk. Always use a secure stand and never touch the tip. Ensure you work in a well-ventilated area or use a fume extractor to avoid inhaling fumes. Wear safety glasses to protect your eyes. Wash your hands after handling materials, particularly leaded solder. This board also carries power: never exceed 20 V on the barrel jack (the limit is set by the IR2113 gate driver). At high output power the MOSFETs and the L7805 regulator can get warm — avoid touching them while the board is powered. 📦 What's Included ✓ PCB — high-quality printed circuit board ✓ Electronic Components — 2 × 555 timers, LM393 comparator, 74HC14 Schmitt-trigger inverter, IR2113 gate driver, 2 × IRLZ44N MOSFETs, L7805 regulator, 22 µH inductor, and all supporting SMD and THD passives ✓ Documentation — full assembly, circuit-theory and troubleshooting guide, plus a printable Assembly Print sheet ⚡ Technical Specifications 🔹 Topology: Discrete Class D (PWM switch-mode) — no amplifier IC 🔹 Output: Mono (stereo input summed to mono) 🔹 Supply voltage: 12–20 V DC via barrel jack (20 V max, set by the IR2113) 🔹 Speaker impedance: 4 Ω or 8 Ω 🔹 Switching frequency: ~188 kHz (555 carrier oscillator) 🔹 Output filter: LC low-pass, ~34 kHz cutoff 🔹 Key ICs: NE555 / LM555 ×2 · LM393 dual comparator · 74HC14 hex Schmitt inverter · IR2113 half-bridge driver · L7805 regulator 🔹 Power devices: 2 × IRLZ44N logic-level N-channel MOSFETs (half-bridge) 🔹 Component type: Through-hole (THD) + SMD (0805)