Audiophile, High Quality T-DAC, RPi-DAC

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T-DAC, RPi-DAC - what is it based on?  [1]

  • 1x PCM1794A - 24bit DAC
  • 4x LME4999 - opamp (soldered)
  • 1x TPA6120A - headphone amp
  • 6x TPS7A4700 - LDOs, power supply
  • 6x Schottky bridge rectifiers, 2A
  • small PCB: double layer, single sided SMD equipped, 3.8 * 2.5 inch (9,6 x 6,4 mm)
  • optional: pre-power-supply with LT317/LT337 or TPS7A4501 (recommended)

Digital Audio Conversion

The DAC is a TI PCM1794A. It is used with I2S format which supports 24bit (only) and 48..192 KHz.

If we would use the Right Justified format we could support also 16bit samples.

A single DAc should be enough. The additional +3dB SNR we cannot process anyway: the headphone audio apmplifier does not provide the needed SNR value.

The schematic is based on the suggestions provided in the manufacturers datasheets [1].

Opamp - I/V Conversion and Filter

For the I/V conversion a high quality OpAmp is used, as LME 49990. It has an amazing SNR parameter and a very low noise figure.

Headphone AMP

A headphone speaker is commonly used. If we use a high quality amplifier it should be possible also to connect a main amplifier with unbalanced input. We would need a voltage divider at the audio output!

The TI TPA6120A seems to have a high SNR parameter and acceptable noise figure.

Power Supply/LDOs

The Power Supply is based on:

  • separate high quality LDOs for every voltage (6x)
  • keep the power rails separate for right and left channel on the +/-15V supplies, for a high channel separation
  • use the TPS7A4700 which has an excellent PSRR parameter and a very low noise
  • use the same TPS7A4700 also for the negative -15V rail. This is possible if we use a transformer with a separate coil and separate full bridge rectifiers. A negative LDO might not have similar parameters.

Schematics - DAC

DAC schematics

Schematics - PSU

PSU schematics

Please, see the datasheet how to ground the control pins in order to have the +3.3V output voltage.

Schematics - Pre-PSU

If you want to reduce the heat dissipation on the PCB or improve the PSRR then you could use such a Pre-PSU

Pre-PSU schematics

PCB - Top


PCB - Bottom

T-DAC PCB Bottom


[1] see detailed circuit datasheets of original manufacturers

T-DAC collection - drawings, schematics, drafts (PDF)