[IDEA] Upgrading my DAC Hat

[hifinet]

ProtoDAC TDA1387 X8 is a perfect project for the beginner. This is probably the easiest DIY NOS DAC HAT build. The number of parts and parts cost can be low.  The TDA1387 is very easy to implement. It directly uses I2S from the Raspberry Pi as input. This circuit is very simple due to the use of passive I/V.  Please refer to the schematic diagram below. The sound quality of the finished DAC is excellent, especially when using premium components. 

There is this proto board version described below, which a seasoned DIYer could assemble in less than an hour. For more updated information follow on the Moode home page and project page here and the ProtoDAC thread here .




This DAC is based on a TDA1387 x 8 module (pictured above), which is designed as a direct plug in replacement for the famous TDA1541, which is now difficult to obtain. The TDA1541 was a flagship Philips multibit 16 bit DAC in a 28 pin DIP/DIL, and is older and more complex. The TDA1387 is a later development multibit DAC with current output, and simplified. The TDA1387 has only 8 pins. The module uses eight TDA1387 chips in parallel. It also contains decoupling capacitors and pin 7 capacitors. The module can be purchased on eBay or AliExpress.

Philips Designers Guide August 1997



TDA1387 Datasheet

The TDA1387 x 8 module has only 8 active pins. Four I2S lines, pins 1,2,3,4 (pins 2 and 4 are the same: BCK). Two power supply lines, V+ pin 28 and GND pin 5. The other two pins are for right channel output pin 6 and left channel output pin 25. The other 20 pins have no connection. Eight power supply decoupling capacitors are mounted on the underside of the module, so it will remain stable with external power applied, without an external decoupling capacitor. The DAC is capable of 16 bits (LSBs over 16 are ignored) and up to 384kHz sample rate. Paralleling the TDA1387 increases the output current capability, and allows the practical use of passive I/V (passive components = fixed resistors generate voltage from current). The combination of I2S input and passive I/V allows for a very simple Raspberry Pi based NOS DAC HAT. 

Schematic


This DAC HAT is built on a GeeekPi Proto board HAT, and is designed for the Raspberry Pi with 40 pin GPIO. Hole spacing is 0.1" . Holes are plated through. The holes can pass up to 20 gauge wire (0.032" dia). GeeekPi is 52pi.com a Chinese tech company. SKU K-0335. The black board model number is X002KJBA7H . They sell the boards on Amazon and AliExpress here and here in four colors red, blue, black and green. Blue appears to be sold out.


Here is some info on the I2S inputs:

Module pin          I2S               Strip GPIO#                 GPIO pin
1                        WS(LRCK)          #19                           35
2                        BCK                  #18                           12
3                        DATA                 #21                           40
4                        BCK                  #18                           12

The GND strips connect to most of the GPIO ground pins, but not pins 6, 9 and 14.

Strip GPIO# (Broadcom I/O #) is the number on the GeeekPi Proto board. 





TDA1387 x 8 Module Pin Assignments:
1           WS (LRCK)
2           BCK
3           DATA
4           BCK
5           GND
6           Right channel audio out
7-24      N/C
25         Left channel audio out
26-27    N/C
28         Vcc +5VDC


28 pin DIP/DIL package



Bench testing the Modules:
Idle right channel voltage pin 6 with 475R I/V resistor at 5.04VDC Vcc     Number tested=9  Average=2.19V  (4.6mA)  SD=0.014
Idle left channel voltage pin 25 with 475R I/V resistor at 5.04VDC Vcc     Number tested=9  Average=2.18V  (4.6mA)  SD=0.02

This DAC can be built on a various types of prototyping boards with 0.1" hole spacing, and using jumper wires to the Raspberry Pi I2S GPIO connections indicated below. The GeeekPi Proto HATs are actually cheaper than buying perf boards + 40 pin headers + standoffs separately. 


I2S Connections on the Raspberry Pi 40 pin GPIO