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The Mute Audio pupDAC

Technical Highlights

Texas Instruments' Highest Quality DAC -
The mute audio pupDAC is based on the Texas Instruments/Burr-Brown's highest quality DAC, the PCM1794. (The slightly less achieving, but less-expensive, PCM1798 can also be used in the pupDAC and is fully pin-compatible.) A PCM2707 (or PCM2706) is used as a USB to I2S convertor which then feeds the signal to the PCM1794 DAC chip. One feature not commonly seen, but similar to the grubDAC, is that the PCM2707/6 is clocked by a quality crystal oscillator (Crystek C3392-12), as opposed to a simple crystal. It possesses very good performance for low cost.

(PCM1794A and PCM2707)
Low Voltage Rail-to-Rail Opamp -
Some of the newest, rail-to-rail (very nearly all supply voltage is available for output), low-voltage opamps provide conversion from the differential outputs of the PCM1794 to provide standard analog Left and Right channel signal outputs. The TI/Burr-Brown OPA2835, the new OPA2836, and the National Semiconductor (now TI) LMH6643 opamps are fully compatible and vetted to very low offset in the pupDAC. (Experimenters, have at it for other opamps!).

(TI/National Semi LMH6643)
No Output Coupling Capacitors -
The mute audio pupDAC also differs from most available DIY-DACs through the use of a charge pump voltage inverter (TI TPS60403). This provides a completely differentiated positive and negative voltage supply for the opamp. This means that the pupDAC requires no output coupling capacitors. A trivial 10 ohms resistance is provided on the output of the opamp to remove any chance of hiss if the pupDAC is used to directly feed small, highly-efficient heapdhones.
Every Voltage Source Regulated -
Finally, although completely powered through its USB-connection, every voltage source on the pupDAC is regulated. No less than five Low DropOut (LDO) regulators are provided. An additional supervisory device, the MCP100T, is provided to reset the DAC in case the proper voltages are not available.

We think you will find that the pupDAC is among the finest-sounding and most-sophisticated DIY DACs available that is USB-powered!
PCM1794 specs -
The Texas Instruments/Burr-Brown PCM1794 is a monolithic CMOS integrate circuit that includes a set of stereo DACs and support circuitry using TI's advanced segment DAC architecture. The PCM1794(A) achieves outstanding dynamic performance, signal-to-noise ratio, low distortion, and improved tolerance to clock jitter. The DAC chip uses fully-balanced current outputs. This allows complete control over optimizing the analog performance outside of the chip. Some of the primary features of the PCM1794 DAC chip are listed below:
  • 24-bit Resolution (the pupDAC uses a 16-bit USB connection)
  • Differential Current Output: 7.8 ma p-p
  • Audio Performance:
    -  132dB Dynamic Range (9V RMS, Mono)
    -  129dB Dynamic Range (4.5V RMS, Stereo)
    -  THD + Noise: 0.0004%
  • 8x Oversampling
  • All common sample rates from 10kHz to 200kHz supported
  • +3.3V Digital, +5V Analog operation

(PCM1794 Block Diagram)
PCM2707/6 specs -
Some of the primary features of the PCM2707 are listed below:
  • USB 1.0 specification compliant
  • Supports 12MHz data transfer rate
  • Accepts 16-bit stereo and mono data streams
  • 48KHz, 44.1KHz, and 32KHz sampling rates
  • Clock Generator with 12MHz clock source
  • +3.3V Digital, +5V Analog operation

(PCM2707 Block Diagram)
OPA2835/2836 specs -
  • Ultra Low Power:
    -  2.5V to 5.5V Supply Voltage
    -  250uA Quiescent Current (typ) (1mA - 2836)
  • 56MHz Bandwidth (205MHz - 2836)
  • 160V/us Slew Rate (560V/us - 2836)
  • SNR: -116.4dBc at 1 kHz (-117.6dBc - 2836)
  • THD: 0.00003% at 1 kHz
  • 40mA Output Current (50mA - 2836)
  • Rail-to-Rail Output

LMH6643 specs -
  • Low Power:
    -  2.7V to 10V Supply Voltage
    -  2.7mA Quiescent Current (typ)
  • 130MHz Bandwidth
  • 130V/us Slew Rate
  • SNR: -116.4dBc at 1 kHz
  • THD: 0.079% at 1 kHz
  • 75mA Output Current
  • Rail-to-Rail Output within 40mV

PCB Specs -
1 oz. copper, 0.062" FR4 material, electrically tested:
  • Total number of pins: 257
  • Pins in a net: 242
  • Not connected pins: 15
  • Total number of vias: 50
  • Total number of connections: 194
  • Unrouted connections: 0
  • Completion: 100%
  • Total number of parts: 88
  • Total number of nets: 48

(Production PCB)

Manufacturer data sheets:
PCM1794A PCM2707 PCM2706 (alt)
OPA2835 (alt) OPA2836 (alt) LMH6643 (alt)
TPS60403 TPS79325 TPS79333
TPS793475 TPS72325 MCP100
Crystal Oscillator PCM1798
(alt - lower performance)
file last changed:Saturday, December 8, 2012 6:00:00 AM
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