Hi-Fi Wi-Fi Speaker System

Project DescriptionVideo

THE WIFI SPEAKER SYSTEM

The WiFi Speaker System is an audio system that utilizes a TI BeagleBone Black running a Debian Linux distribution and a uPnP renderer as a Plug-and-Play wireless audio system through the use of the Advanced Linux Sound Architecture (also known as ALSA) and a 32-bit stereo DAC, a Burr Brown (owned by TI) PCM5102. The amplifier uses an active crossover utilizing several TI NE5532 and two National Semi (now TI) LM3886 Class AB monolithic amplifier chips per amplifier. The amplifier is completely integrated on to a plate amp which also holds a power transformer. The crossover includes baffle step compensation for lower frequencies, and a time delay circuit to achieve the best phase performance across frequency. The power supply uses a LM317 (NS) and a LM237 (TI). The system also features a relay to protect the speaker drivers from transients from turning the speaker on or off (also known as turn-on thump). The relay is driven by a TI Darlington pair IC with integrated flyback diodes, the ULN2003. Should the speaker be used without the uPnP renderer, the input may be left channel, right channel, or balanced (which is typically used in professional settings to increase CMRR). The input is selected through the use of a switch on the board. A Burr-Brown (owned by TI) INA134 takes the balanced signal and converts it to a single ended signal for use by the amplifier. All of the signals are transformer isolated and then buffered by a NE5532 and output into another 1/4" stereo jack. This allows for paralleling as many identical speakers as desired to increase the volume. The amplifier includes circuit board mounted transformers that eliminate ground loops that can be introduced through the interfaces between audio equipment and present an annoying hum that is very difficult to eliminate. Since these transformers have a high impedance coupling from the power transformer and nearby equipment, the amplifier has a novel circuit that loads the input when it detects there is no music playing. This eliminates the hum. The board has holes along the edge to allow for mounting of the amplifier to an aluminum plate that also acts as a heatsink for the power LM3886s. Overall the WiFi speaker system is an audio system that can not only compete with other lower bitrate options like Bluetooth, but beats them in almost every way. Please refer to the PDF in the attached zip file for full documentation.


PROJECT FEATURES:

  • Full range - 25Hz to 36kHz
  • Excellent noise performance
  • uPnP - a full-featured widely-used protocol for streaming high-quality audio
  • Plug-and-Play
  • Class AB amplification - reduces switching noise apparent in Class D and other switching amplifier topologies
  • Wireless - just requires a WLAN access point or switch
  • Single ended stereo or balanced (differential) input
  • Transformer isolated inputs - reduces ground loop hum
  • Active crossover and biamp configuration - improved linearity and superior crossover performance in amplitude and phase
  • Buffered outputs - allows for paralleling multiple speakers
  • Input loading reduces coupling from external sources when no music is playing using analog audio detection
  • Relay output to speakers - eliminates turn-on thump