• Status: Draft / requirements review
• Production-intent compact 5.1-channel Class-D audio amplifier for a Kickstarter launch.
• Target retail price: approximately US$350.
• Initial planning quantity: 100 units, with architecture and sourcing suitable for scaling after crowdfunding.

• Indoor home speaker systems using passive 4–8 ohm speakers.
• Compact, externally powered unit with retro styling and modern digital inputs.
• First build will be a validation prototype followed by a 100-unit pilot run.

• Drive front left/right, rear left/right, center, and passive subwoofer channels.
• Accept stereo audio from RCA, 3.5 mm AUX, Bluetooth, optical PCM, and Tape Play inputs.
• Create selectable multichannel playback from stereo sources; licensed Dolby/DTS decoding is not required.
• Provide both an amplified passive-subwoofer output and a line-level RCA output for a powered subwoofer.
• Provide intuitive input, volume, and playback-mode controls.

• Six amplified outputs targeting 50 W/channel into 4 ohms, compatible with 4–8 ohm speakers.
• Six insulated panel-mounted 5-way binding-post pairs (banana/spade/bare-wire compatible) for FL, FR, RL, RR, center, and passive subwoofer. No verified binding-post library footprint is currently available, so the PCB retains 14 A two-pin terminal symbols as the internal harness landing points; production panel binding posts connect to these terminals.
• Stereo RCA input.
• Stereo Tape Play In and fixed-level Tape Record Out RCA connections.
• Optical TOSLINK input supporting stereo PCM.
• Bluetooth audio input.
• 3.5 mm stereo AUX input.
• Powered-subwoofer RCA line output.
• Amber-tinted display with animated twin digital VU meters, volume, input, Bluetooth, and playback-mode indication.
• Retro-modern controls, including a prominent physical volume control.

Diagram

• Low-noise analog input switching for RCA, AUX, and Tape Play.
• Optical S/PDIF receiver limited to supported stereo PCM formats.
• Bluetooth audio module or certified radio module to reduce RF certification risk.
• Tape Record Out should follow the selected analog/audio source at fixed line level and remain independent of the main volume setting.

• Stereo-to-multichannel modes: stereo front-only, all-channel stereo, and synthesized surround.
• Center-channel generation and adjustable subwoofer low-pass filtering.
• Per-channel trims, mute, master volume, startup ramp, and configurable speaker protection behavior.
• No Dolby Digital or DTS licensed decoding in the initial product.

• Efficient Class-D architecture.
• Design target: 6 × 50 W into 4 ohms under defined test conditions.
• Must remain stable with 4–8 ohm nominal loads and include overtemperature, overcurrent, undervoltage, and output fault protection.
• Thermal design and honest simultaneous-power rating must be validated before marketing claims are finalized.

• Amber-tinted graphical display styled as twin analog VU meters.
• Large physical master-volume control.
• Input and playback-mode selection controls.
• Display brightness control or dimming mode recommended.

• Rear insulated 5-way binding posts are the production user interface. The schematic's existing 14 A two-pin terminal blocks are retained only as internal harness/PCB landing points because no verified usable binding-post library part was found.
• Reverse-polarity and surge protection at the DC input.
• ESD protection on externally accessible low-voltage signal connectors.
• Service/debug access retained internally for production testing and firmware updates.

• Powered from a certified external DC adapter; no mains voltage on the amplifier PCB.
• Preliminary adapter range: approximately 36–48 V DC.
• Peak adapter capability may need to be approximately 8–10 A, subject to amplifier topology, crest factor, thermal limits, and the finalized continuous-power specification.
• “Portable” means compact and movable between locations; battery operation is not currently included.

Diagram

• Six channels at 50 W equals 300 W of theoretical audio output; sustained all-channel output would require substantial adapter and thermal capacity.
• Consumer audio normally has lower average power than sine-wave bench testing. The final specification must separately state per-channel test power and all-channels-driven continuous power.
• Detailed rail-by-rail budget is required before selecting the adapter, connectors, protection components, and regulators.

• Initial pilot target: 100 units; design must use readily sourced, assembly-friendly components and avoid unnecessary hand wiring.
• Kickstarter demand is uncertain, so the BOM should support alternative approved sources and scalable procurement.
• Prefer a certified Bluetooth module and certified external power adapter.
• Production PCB assembly with test points, programming access, serial-number support, and a repeatable functional test fixture.
• Connectors and controls should be mechanically secured for consumer use rather than relying only on solder joints where practical.

• Control master volume, mute, input selection, playback mode, display, VU animation, channel trims, and subwoofer settings.
• Save user settings in nonvolatile memory.
• Manage pop/click suppression and amplifier enable sequencing.
• Provide a protected firmware programming/debug interface.
• Firmware update method and remote-control support remain to be decided.

• Compact tabletop enclosure with retro-modern visual treatment.
• Amber display and prominent volume knob on the front.
• Signal inputs, external DC power, and speaker outputs arranged clearly on the rear.
• Ventilation and heatsinking must be designed from measured thermal results.
• Exact dimensions, enclosure material, remote control, and connector layout remain open.

• External certified DC power brick instead of an internal mains supply.
• Stereo PCM optical processing instead of licensed Dolby/DTS decoding.
• Stereo sources are converted to selectable multichannel modes in DSP.
• Both passive and powered subwoofer outputs are included.
• Digital VU display selected over mechanical meters to reduce cost and share the display with status information.
• One general stereo RCA input plus a traditional tape loop; no six-channel direct analog input.

• The 50 W/channel target applies primarily at 4 ohms; output into 8 ohms will normally be lower unless a higher-voltage or bridged architecture is selected.
• The passive subwoofer channel has the same nominal 50 W target as the other channels, though a higher-power sub channel may be evaluated later.
• Bluetooth codec requirements, remote control, headphone output, USB audio, EQ depth, enclosure dimensions, and detailed compliance markets are not yet specified.
• Product is intended for indoor consumer use.

• The feature set is feasible near the $350 retail target, but BOM discipline is important due to six power channels, the high-power adapter, enclosure, display, connectors, and certification costs.
• Thermal performance, EMC from multiple Class-D channels, Bluetooth/radio compliance, and truthful power labeling are primary engineering risks.
• A 100-unit pilot favors modular/certified wireless and power solutions; custom tooling should be minimized until Kickstarter volume is known.

• All inputs operate without audible switching pops or objectionable noise.
• Stable operation with specified 4–8 ohm test loads.
• Protection safely handles shorts, overheating, undervoltage, and abnormal loads.
• Six channels and powered-sub output follow configured DSP modes and volume behavior.
• Tape loop behaves as a conventional fixed-level record/send and playback/return interface.
• Product passes defined audio, thermal, safety, EMC pre-compliance, and production functional tests.

• Primary adapter target: certified 48 V / 8 A; 36 V operation is reduced-power.
• Six outputs implemented as three stereo BTL Class-D stages suitable for a 48 V rail.
• Dedicated audio DSP and multichannel converter provide front stereo, all-channel stereo, synthesized surround, center generation, sub low-pass, trims and master volume without licensed Dolby/DTS decoding.
• Certified Bluetooth module, dedicated optical S/PDIF receiver, control MCU, graphical display interface, rotary encoder, buttons, debug/programming and nonvolatile settings are included.
• Detailed calculations are maintained in the separate Power Budget project file.

• Initial specification created from product-definition discussion.
• Captures 6 × 50 W target, input set, tape loop, dual subwoofer support, external power, amber digital meters, $350 retail goal, and 100-unit pilot plan.
• Added production architecture, 48 V / 8 A adapter target, realistic 6 × 35 W all-channels continuous design target, and explicit per-channel versus simultaneous-power distinction.
• Selected primary parts: 3 × TI TPA3255DDVR, ADI ADAU1467, TI PCM3168A, Microchip BM83, STM32G0B1R, TI DIR9001, and MPS MP4572 rails.
• Added datasheet-based 12 V, 5 V, and 3.3 V rail support; three TPA3255 BTL blocks with 33 nF bootstrap capacitors, 10 uH + 1 uF output filters, differential codec coupling, shared fault/reset/mute sequencing nets, and floating BTL speaker pairs.
• Binding-post library search found no verified 5-way binding-post footprint; retained PCB terminal symbols and documented panel wiring strategy.
• Open optical item (does not block unrelated circuitry): no active-production PLR237/T10BK-class TOSLINK optical receiver module with a verified usable symbol/footprint was found in the Flux library. JOPT1 is an electrically valid internal 3V3 / GND / SPDIF_RX header feeding DIR9001 RXIN, so a later documented production optical-receiver board/module can be connected without a mock part.
• Input protection open item: F1 provides an 8 A time-delay fuse position and the 6,000 uF/63 V bulk bank is populated, but the 48 V/7.5 A path still requires a verified ≥80 V, ≥15 A reverse-polarity ideal-diode stage, surge clamp, and active or relay-bypassed inrush limiter. No verified complete library solution was found; direct connection of the final production bulk bank without this stage is not approved.
• Current schematic is an architecture population only and is not electrically complete: support passives, external I/O connectors, protection, wiring, no-connect markings, and ERC remediation remain required.