DualMono - Why?

• two DAC boards, each running in Mono mode - provides +3dB SNR (on DAC)
• better heat dissipation - Amp TPA6120 used for one channel only (less heat, higher margin)
• higher stereo channel separation - each channel with not shared signal path
• could be used for Mono applications, with 132dB SNR on DAC

How does it sound?

This Dual-Mono DAC sounds really great. Impressive, never heard all the details.

I think it is not due to fact that two DACs as Dual-Mono (one DAC drives one channel with sum of a single DAC output). It is more related to the fact, that entire system was optimized, the signal chain was trimmed for best performace (e.g. let run the OpAmp and Headphone Amp in better operation mode).

Digital Audio Conversion

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

Two of the Mono DAC boards are used for a stereo Dual-Mono setup. It will make use of the PCM1794A DAC features, e.g. with additional +3dB SNR.

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.

One DAC drives one channel. The DAC runs in Mono mode and the DAC output is combined to one signal. One board is used for one stereo channel.

Block Diagram - Dual Mono DAC

Schematics - Dual Mono

PCB - Top

PCB - Bottom

Remark: two of these PCBs are needed for a stereo setup. The connectors are designed in a way that all can be stacked directly with male and female connectors, without flying wires, including to use the RPi-DAC SPS

BOM

Design files and docs

BOM_RPi-DAC_DualMono.pdf (69K)

RPi-DAC_DualMono_parts.pdf (458K)

RPi-DAC_DualMono_soldering.pdf (148K)

UltraDAC_RPi_mono.zip (80K) ExpressPCB file (ZIP)

Pictures

References

[1] see detailed circuit datasheets of original manufacturers

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