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I wanted to build high quality preamplifier with built-in DAC from SPDIF or USB for my power amplifier Leachamp. I had available circuit PCM2902. I tried to design DAC from USB with this circuit on one-sided PCB and I was succesful.

I needed high quality DAC convertor from USB to S/PDIF. Circuit has analog output for headphones and digital S/PDIF output with electrical and optical(TOSLINK) interface. We can use too 3 HID buttons for setting volume and mute. For USB input is used standard miniUSB connector. Headphone output uses standard 3.5" stereo jack socket. For signal conversion from TTL level to differential signal is used RS-485 bus transceiver. For optical output is used optical transmitter TOTX173 from Toshiba.

Presented here is high quality USB DAC PCM2906 with built-in headphone amplifier. To see one or more of the same sound card than this is a compact device. That acts as the computer sound card is easy to use. Just plug into a USB port on your computer. It can be used immediately within an IC in PCM 2906 Burr Brown's brand of Neu hear all agree that the sound of course. Used to convert digital signals from the USB port can adjust volume and mute the signal with Noise from the hard drive or CD player can not come to interference. Because a separate circuit from the computer. Add power to drive headphones with a Single Supply OPA2353 Opamp serves as Headphone Amp that does not reconcile the external power supply. This may be an alternative for those who are looking for sound card priced tight, but the quality of glass.

This audio amplifier uses TDA7053 which is an integrated class-B stereo power amplifier in a 16-lead dual-in-line (DIL) plastic package. Which requires minimal amount of external parts. This might be good solution to all of those who have PC with integrated sound card into motherboard. The main problem is that outputs of such sound cards are for active acoustic systems, this means that speakers must have power amplifier built in. If you decide to connect a headphones sometimes it might be not enough to provide required sound level.

This is USB sound card with PCM2902 chip. For the purpose of testing the D / A converters, I built a simple USB sound card with the circuit PCM2902. The card has analog input and output, an electrical S / PDIF output, galvanically separated input and optical input and output TOSLINK. The heart of USB sound card is PCM2902 it is a circuit connection, which is a complete USB codec. The circuit can handle up to 48kHz sampling frequency. The integrated circuit includes a USB controller for A / D and D / A converter, HID part for 3 buttons, volume control, custom converters and S / PDIF encoder and decoder.

The voice messages are recorded into the on-board microphone, then each message can be individually triggered by an external signal. The inputs can respond to simple electrical contacts, logic levels or voltages, and all inputs are debounced to prevent false triggering by electrical noise. Each message can be arranged to play once on a selected change of input state (high-to-low or low-to-high), or to repeat continuously until the trigger condition is removed. These options are selected by DIP switches.

This is a scaled-down version of Nelson Pass' Zen power amplifier for my headphones. For this use, the Zen topology is perfect excellent sound quality, simplicity, linearity and no multi-stage feedback. It is a single stage class A MOSFET design with the right gain and a low output impedance. Here we don't have the limitations of the Zen amps at least in the single-stage implementations regarding speaker compatibility. A single stage topology with correct interfacing values misses very few things in the original music message. The gain device in the original Zen amplifier is biased by fixed current source. For this amp, I employed an active current source described in Pass' patent no. 5,710,522 (see Zen Variations Part 2). The benefits of an active source include higher output current, lower distortion and 50% theoretical operating efficiency (compared to the 25% efficiency from a fixed source). This type of current source is featured in the Aleph power amplifiers from Pass Labs.