NeXT: SoundBox mini

Frank Gregor
Frank Gregor

Interactive technical showcase of the NeXT SoundBox mini, presenting 3D model visualization, complete circuit schematics, and detailed component documentation with full Bill of Materials and part specifications.

Functional Overview

This is a replica of the NeXT SoundBox on a scale of 1:2 with a custom USB-Audio controller board, which drives a mono speaker. The circuit converts digital audio data from the USB port into an analog signal, amplifies it, and outputs it to a speaker. The following diagram shows the path from data to sound.

Component Blocks in Detail

The circuit is divided into four main functional groups.

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flowchart LR
   USBInput("**USB Input**") --> USBDAC("**USB DAC**")
   USBDAC --> StereoMono("**Stereo to Mono**")
   StereoMono --> MonoAmp("**Mono Amplifier**")

   USBInput:::usbinput
   USBDAC:::usbdac
   StereoMono:::stmono
   MonoAmp:::monoamp

   classDef usbinput fill:#9fe4c1,stroke:#00b11e,stroke-width:2px,color:#00b11e
   classDef usbdac fill:#d4c1e7,stroke:#972edf,stroke-width:2px,color:#972edf
   classDef stmono fill:#b3d1e6,stroke:#005eb1,stroke-width:2px,color:#005eb1
   classDef monoamp fill:#e2b7ba,stroke:#dc002b,stroke-width:2px,color:#dc002b

   style StereoMono stroke-width:1px,stroke-dasharray: 0
   style MonoAmp stroke-width:1px,stroke-dasharray: 0

USB Input

This part of the circuit is the interface to the outside world. It receives power and data from the USB port, filters the voltage, and protects the entire circuit from electrostatic discharge.

USB1: USB Type-B Jack

Physical interface to the host. Provides +5V (VBUS), Ground (GND), and the differential data lines D+ and D-.

L1: Ferrite Bead

Filters high-frequency noise from the USB power supply before it reaches the circuit.

U1: USBLC6-2P6 (ESD Protection)

The USBLC6-2P6 protects the sensitive data lines (D+, D-) and the VBUS line from damage caused by electrostatic discharge.

LED1 & R1: Power Indicator

A green LED connected directly to the 5V line to indicate that the USB port is supplying power.

USB DAC (PCM2706PJT)

The PCM2706PJT is a USB audio codec that integrates a complete stereo digital-to-analog converter (DAC) with USB interface functionality on a single chip. It appears as a standard USB audio device to any host computer, requiring no custom drivers, and converts digital audio data received over USB into high-quality analog stereo output signals. The chip includes an integrated USB transceiver, digital audio processing, and stereo DAC with built-in headphone amplifier, supporting sample rates up to 48kHz at 16-bit resolution.

U5: PCM2706PJT

The heart of the circuit. This chip is a stereo audio DAC with an integrated 3.3V LDO. It is powered by the 5V VBUS and generates its own internal supply voltages.

X2, C30, C31, R13: Oscillator Circuit

A 12MHz crystal with appropriate circuitry generates the precise clock signal required by the PCM2706 for USB communication and audio synchronization.

C24, C26, C27, C28, C29: Decoupling Capacitors

These capacitors are placed directly at the power supply pins of the DAC to stabilize the internally generated voltage and filter high-frequency noise, which is crucial for good audio quality.

Stereo to Mono

This simple passive circuit combines the left and right audio channels from the DAC into a single mono signal and prepares it for the mono amplifier.

R3, R4, C4: Passive Mixer

Resistors R3 and R4 (10kΩ each) mix the left and right channels from the DAC into a single mono signal. Capacitor C4 couples this signal to the amplifier and filters out any DC component.

Mono Amplifier (PAM8302A)

The PAM8302A is a Class-D mono audio amplifier integrated circuit that converts low-level audio signals into amplified output capable of driving small speakers directly. It delivers up to 2.5W of power into a 4Ω speaker while maintaining high efficiency of up to 90%, making it ideal for battery-powered portable devices. The chip features built-in thermal and overcurrent protection, requires minimal external components, and operates from a single 2.5V to 5.5V supply.

U3: PAM8302A

An efficient Class-D mono audio amplifier. It takes the weak mono signal at the input (Pin 3) and amplifies it to drive a speaker.

Full Schematic

Bill of Materials

| Reference | Value/Designation | Package | Description | LCSC Part # |
|-----------|-------------------|---------|-------------|-------------|
| USB1 | USB-B01 | THT | USB 2.0 Type-B Jack | [C498173](https://lcsc.com/product-detail/C498173.html) |
| LED1 | KT-0805G | 0805 | Standard green LED | [C2297](https://lcsc.com/product-detail/C2297.html) |
| R3 | 10kΩ | 0402 | Mixing/Pull-down resistors | [C25744](https://lcsc.com/product-detail/C25744.html) |
| C30 | 22pF | 0603 | Load capacitors for crystal | [C105620](https://lcsc.com/product-detail/C105620.html) |
| C24 | 1uF | 0603 | Decoupling capacitors for DAC | [C15839](https://lcsc.com/product-detail/C15839.html) |
| C3 | 100nF | 0805 | Decoupling/Coupling Capacitor | [C1525](https://lcsc.com/product-detail/C1525.html) |
| C28 | 100uF | TAJB | Bulk bypass capacitor | [C16133](https://lcsc.com/product-detail/C16133.html) |
| C32 | 220uF | RVT | Bulk bypass capacitor | [C2887273](https://lcsc.com/product-detail/C2887273.html) |
| H1 | KF128-5.08-2P-AA | 5.08mm | 2-Pin Screw Terminal Block | [C474952](https://lcsc.com/product-detail/C474952.html) |
| L1 | BLM18PG121SN1D | 0805 | Ferrite Bead for noise suppression | [C14709](https://lcsc.com/product-detail/C14709.html) |
| R1 | 220Ω | 0805 | Current limiting resistor for LED | [C25951](https://lcsc.com/product-detail/C25951.html) |
| R13 | 1MΩ | 0603 | Parallel resistor for crystal | [C105578](https://lcsc.com/product-detail/C105578.html) |
| R14 | 1mΩ | 0603 | Pull-down for DAC Pin 1 | - |
| U1 | USBLC6-2P6 | SOT-666 | ESD protection for 2 data lines and VBUS | [C15999](https://lcsc.com/product-detail/C15999.html) |
| U3 | PAM8302AASCR | SOP-8 | 2.5W Class-D Mono Audio Amplifier | [C113367](https://lcsc.com/product-detail/C113367.html) |
| U5 | PCM2706PJT | TQFP-32 | USB Stereo Audio DAC | [C1519999](https://lcsc.com/product-detail/C1519999.html) |
| X2 | 12MHz | 3225 | Crystal Oscillator | [C9002](https://lcsc.com/product-detail/C9002.html) |