Background

Always fighting for the best audio solution, trying other nice DACs such as Weiliang DAC 3 [1], Weiliang DAC5 [2], loving the Wolfson WM DACs [3], experienced in audio electronics, SoC etc. - I have checked out existing solutions: Is it really possible to build a real 24-bit DAC, to get out all the 24-bit?

Is there a way to make it even better?

Yes, there is, but no way to get out all 24-bits, neither by purchasing commercial products.

T-DAC, RPi-DAC is a modular concept and allows to combine with several interfaces such as Bluetooth, USB, S/PDIF, TOSLINK etc.

Requirements

I have defined the following requirements when designing my solution:

• select a DAC with: best SNR, lowest THD+N - try to get out 24-bit, I need 144dB
• select opamps with lowest noise, supporting high SNR - try to get out 24-bit, lowest noise
• use a headphone amp, usually listen with headphone - keep it small, use SMD
• headphone amp with specs. supporting high SNR and low THD+N - do not jeopardize later
• design power supply with low noise, especially high Power Supply Ripple Rejection (PSRR) - avoid any hum and noise injection
• have a high channel separation: use separated, dedicated power rails
• design system for the best performance (entire signal path) - check the weakest circuit in path

The goal was to achieve at least 120dB SNR (20-bit resolution). Knowning the fact, for a real 24-bit output I would need 144dB SNR (6 dB per bit as rule of thumb) I was pretty sure: all solutions offered as 24 or even 32-bit are just marketing jokes. There cannot be a real 24-bit DAC. But reasonable to fight for the best performance, I did.

Solution

I thought first: Dual-DAC, as offered as the best way. But why? Do I get out really the additional +3dB SNR just by designing a Dual-DAC? No.

Is my headphone, even using the best one of class, Sennheiser HD800, capable to let me listen to? No.

OK, design a Single-DAC but still with the best performance possible, even I would not be able to realize the improved quality (Blue Book audio CDs as main sound source do not provide the quality I could process). The worst part in the system is the headphone. It will never be able to make use of additional +3dB SNR.

I deciced to design a prototype, using the state-of-the-art curcuits, to solder on a professional PCB and bring it up on XynergyXS FPGA [4] platform.

If you want to start smart: RPi-DAC-RCA. It is a cost-effective alternative for HifiBerry and provides more options, including to have the P1 on PRi still fully available.

How and where to use

The T-DAC should be connected to an FPGA board, e.g. the XynergyXS [2] and also to a Raspberry Pi. The interface is I2S.

A microcontroller, e.g. the Cortex-M4 as STM F4 on XynergyXS, or the BCM2835 on Raspberry Pi should be able to drive it. It gives the opportunity to use it as USB Sound Card or as a Media Center Solution.

T-DAC, RPi-DAC Block Diagram

T-DAC Block Diagram

T-DAC, RPi-DAC and SPDIF/TOSLINK/USB

T-DAC, RPi-DAC with S/PDIF, TOSLINK

RPi-DAC and TOSLNK, S/PDIF, e.g. for iMAC

T-DAC, RPi-DAC and USB

T-DAC, RPi-DAC with USB, S/PDIF, TOSLINK

RPi-DAC and USB, TOSLNK, S/PDIF, e.g. for PCs

T-DAC, RPi-DAC and XMOS USB

T-DAC, RPi-DAC with XMOS USB (eval board)

T-DAC and XMOS USB

T-DAC, RPi-DAC and XynergyXS FPGA

T-DAC, RPi-DAC with FPGA board XynergyXS

T-DAC and XynergyXS FPGA

T-DAC, RPi-DAC and Raspberry Pi

T-DAC, RPi-DAC DualMono with Raspberry Pi (RPi)

T-DAC and Raspberry Pi

RPi-DAC for Raspberry Pi

T-DAC, RPi-DAC and STMF4 Discovery

RPi-DAC with STMF4 Discovery (STMF4 Disco)

T-DAC, RPi-DAC and STMF4 Discovery

RPi-DAC with STMF4 Discovery (Disco)

T-DAC, RPi-DAC and FPGA

RPi-DAC DualMono with STMF4 Discovery (STMF4 Disco) and CmodS6 FPGA

T-DAC, RPi-DAC, STMF4 Discovery and CmodS6 FPGA

T-DAC, RPi-DAC and Bluetooth

RPi-DAC with RN52 Bluetooth module

T-DAC, RPi-DAC and Bluetoothi: stream audio from your smartphone

T-DAC - Module System

The T-DAC is a highly modular system

• as SingleStereo (1 DAC) or DualMono (2 DACs, better SNR)
• with interface modules, Switched Power Supply Unit
• modules with same form factor, directly stackable

RPi-DAC with all modules

Customize the RPi-DAC for your needs. Combine modules and have a great flexibility.

T-DAC Kit - flexible options

There are several options in oder to combine the RPi-DAC modules:

• with Raspberry Pi (RPi) as Network Player, SingleStereo or DualMono, or use with Volumio [5]
• with XMOS USB eval module as USB Sound Card
• with RPi-SPDIF as S/PDIF, TOSLINK or (with XMOS Module) as universal sound card
• with RN52 Bluetooth receiver module for wireless audio from smartphone
• with FPGA module for I2S filtering, upsampling
• T-DAC-IF interface module for several input/output interface and enclosure

Combine the RPi-DAC for your needs

Pictures

References

[1] Weiliang DAC3

[2] Weiliang DAC5

[3] AudioCodec

[4] Bayer DSP XynergyXS

[5] Volumio

[5] HiFiBerry - another Raspberry DAC