By: @hifinet (c) 2023
Edited by @Tim Curtis
Updated: 2024-01-27
This document describes the ProtoDAC TDA1387 X8 Non-Oversampling (NOS) Digital to Analog Converter (DAC) including technology, component sources and instructions for building the DAC.
The information (software) in this document is distributed under the MIT license which includes the following disclaimer:
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
This means that the user of this software is responsible for any damage resulting from its use. It does not matter if the damage is caused by incorrect usage or a bug in the software.
- 1. Introduction
- 2. Printed Circuit Board (PCB)
- 3. Component parts
- 4. Assembly
- 5. moOde audio player
- 6. Appendix
The ProtoDAC TDA1387 X8 [ProtoDAC] is a DIY DAC based on the vintage Philips TDA1387 multibit DAC chip in an eight chip module as pictured below. The chips are configured in parallel with decoupling capacitors and pin 7 capacitors on the underside of the module.
The module 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 Dual In-line Package (DIP), and is older and more complex. The TDA1387 is a later development multibit DAC with current output, and simplified having only 8 pins.
The TDA1387 is a very interesting 16-bit design and represents the end of the multibit DAC era. It uses continuous calibration of the five most significant bit current sources, so it has 32 current sources and one spare source. Philips multibit DACs are also unique in that they do not use resistors like some other DACs, but instead use active devices to generate the currents.
The ProtoDAC is one of the easiest NOS DAC's to build. The number of components is low and the circuit design is simple since the TDA1387 directly uses I2S from the Raspberry Pi as input and passive I/V is used for the output stage.
Most importantly, the sound quality of the finished DAC is excellent, especially when using premium components.
The PCB dimensions and layout conform to the Raspberry Pi "Hardware Attached on Top" (HAT) requirements including the standard 40-pin General Purpose Input Output (GPIO) header. All components are attached using through-hole soldering.
NOTE: This is not final PCB revision
The Computer Aided Design (CAD) drawing of the PCB shows the board layout and location of the component parts. The design allows for several component variations including axial or radial output I/V capacitors, RCA jacks or direct wiring to PCB L/R channel out and 5V power from GPIO or via direct wiring to PCB.
| Reference designator | Component | Description |
|---|---|---|
| C1,C2 or C5,C6 |
Output capacitors | Polypropylene Film 4.7-10uF. Radial leads with 37.5mm LS and Axial leads with 49mm LS using RCA jacks, and up to 54mm LS without RCA jacks. |
| C3,C4 | Electrolytic capacitors | Audio grade 1000uF 6.3V, 10mm diameter and 5mm lead spacing. Nichicon FG (Fine Gold) or KA paired with a Panasonic FR-A adds clarity, with a wide open range and more air up top. Better than two Nichicons in testing. |
| H1 | GPIO Header | Female 2X20P 40 position header connector 0.100" (2.54mm) through hole gold. DigiKey S7123-ND or eBay/AliExpress |
| R1-R3 | Film Resistors | Generic metal film 430R or 470R 1/4W Stackpole RNMF14FTC430R/RNMF14FTC470R or similar. |
| R4-R5 | Foil Resistors | Audio grade Bulk Metal Foil, through hole 420R. Texas Components TX2352 or TX2575 (Vishay) https://www.texascomponents.com/store/home.asp or Charcroft in EU |
| U2 | TDA1387 Module | TDA1387 x 8 Parallel Module Substitution for TDA1541. Available on eBay/AliExpress search "tda1387 tda1541" or "hifi 8pcs tda1387" |
| L/R | RCA Jacks | CA right angle PCB mount RJ-255A. Available on eBay/AliExpress search "RCA PCB DAC" |
Below is a block diagram of the circuit.
Below are the pin mappings for the GPIO header and TDA1387 X8 Module.
| X8 Module pin | I2S function | GPIO number | Broadcom pin |
|---|---|---|---|
| 1 | WS (LRCK) | 19 | 35 |
| 2 | BCK | 18 | 12 |
| 3 | DATA | 21 | 40 |
| 4 | BCK | 18 | 12 |
The module is implemented as a 28 pin DIP and is connected only by pins 1-6, 25 and 28. Note that pins 2 and 4 are internally connected.
|
|
Component parts for the DAC are readily available from various suppliers but since the Philips TDA1387 chips are not produced anymore the 8 x Parallel Chip Module long term availability cannot be guaranteed.
The TDA1387 Integrated Circuit (IC) chips on the module are configured in parallel with decoupling capacitors and pin 7 capacitors on the underside of the board.
The chips are used and originate from the overseas chip-pull industry. Generally they are of high quality but since they are used there is a greater probability of receiving a defective part compared to new parts.
The image below shows an example chip from each of two modules. Note the orientation of the name "Thailand".
I worked with diyAudio user @stellarelephant, and we listened to many types of I/V resistors. We concluded that Metal foil are superior by a wide margin.
Vishay naked bulk metal foil are unsurpassed, and sound very transparent with excellent detail. This may be due to the very low noise or non-inductive design. The improvement in detail compared to other resistor types is dramatic.
Bulk metal foil can be ordered to spec, but they are expensive. Metal film sound OK, and have the advantage in that they are abundant and cheap. I would recommend starting with metal film to hear the possibilities of the DAC, and then move up to Vishay metal foil resistors (if not Z-foil, then S-foil) if you think the DAC shows promise.
The resistor value is critical to avoid clipping at 0dB. The I/V resistor should be no larger than 430R for Vcc of 5 VDC. I measured THD with 0 dB 1kHz sine wave input to the DAC with various I/V resistances. See the chart below. Distortion at 223.5R is measured at 0.0080% and at 322R it is 0.0097%, and THD increases linearly with resistance up to just past 430R. Then distortion starts to increase exponentially, indicating clipping.
Excessive distortion is created when the DAC is clipping. Fortunately, the TDA1387 has a high voltage compliance of 3.5V at 5V Vcc. Clipping occurs if the AC signal exceeds +3.5V or 0V. The final calculation depends on the I/V resistance and the module with its particular characteristics (DC current at idle, and the peak to peak current at full signal). The I/V resistor should be no larger than 430R for Vcc of 5 VDC.
The Vishay Z-foil resistors from Texas Components (TX2575) come in either 470R (too high) or 390R (possibly too low) as a standard resistance, but not 430R. They sell custom values for the same price. Charcroft does sell a Z-foil resistor in 430R. Note the tolerance is +/- 0.1%.
The output signal voltage decreases with a lower I/V resistor, and this may be a factor to consider in your particular system. Do you have a preamplifier that can amplify a weak signal from the DAC?
The source of Vishay S and Z-foil resistors in the US is Texas Components, and in Europe it is Charcroft . TX2575 are about $13 each without shipping. The TX2352 or S-foil is the "original" foil naked audio resistor, and are about $9 each. The Vishay S and Z foil resistors are vastly better performing in this DAC than other types.
Use 430R or 470R generic 1/8 or 1/4W metal film. The purpose is to limit high frequency noise on the I2S lines. I have used unshielded 10cm jumpers to an outboard proto board without a problem. Mount close to the module.
The choice of Vcc electrolytic decoupling capacitor depends on the value of the I/V resistor in an inverse relationship.
As the I/V resistor decreases, the capacitor needs to increase. If the capacitor is too low in value for the I/V resistor, the sound with be anemic, with weak bass and dynamics, but more 3D with deep soundstage. If the capacitor value is too high for the I/V resistor, the depth of soundstage will decrease.
For a 430R I/V resistor, 1800-2200uF is about right.
These capacitors can vary considerably in size, quality and price. You may want to press fit these in place to try different types before soldering.
The value should be around 10 uF, but can be as low as 4.7 uF. With standard 10k impedence, 10 uF will give a low frequency -3dB of 1.59 Hz. 4.7 uF will give a low frequency -3dB of 3.38 Hz. You want the low frequency cutoff to be well below 20 Hz, ideally less than 2 Hz.
A metal foil and film capacitor will be the highest quality, but physically larger and more expensive.
A basic polypropylene metallized film capacitor is a WIMA MKP4 or MKP10 with radial leads. Digi-Key has MKP4D046806F00JSSD which is a 6.8uF 100VDC currently in stock. WIMA MKP are commonly available, competent sounding and are a good choice for this project. Generally, most polypropylene capacitors will be satisfactory. Panasonic ECW and EZP PP caps are good, and relatively small for capacitance. PP caps can also be purchased from speaker components suppliers, where they are used as crossover caps. For example, Parts-Express, Madisound, Speaker City USA, etc. It is best to get the lowest voltage rating available, which will reduce the size. Panasonic, Solen and WIMA PP caps tend to be neutral sounding without any annoying qualities. Humble Homemade Hifi has some capacitor ratings.
Boutique film capacitors can be very expensive and are often too large for the available space on the HAT. Metallized polypropylene tend to be the best value.
Assembly consists of installing and soldering the components to the PCB. Use a high conductivity, 60/40 (Tin/Lead), rosin core, fast melting solder for example Kester 0.031 inch diameter steel-based solder.
- Mount the 40 pin female header (H1) to the bottom, and solder to the pads on the top. Double check the solder joints on pins 2,4,6,12,35,40.
If you are planning to use ProtoDAC with one of the Ian Canada reclockers, please note that these reclockers have a nonstandard GPIO. View this thread for more information https://moodeaudio.org/forum/showthread.php?tid=5531&pid=51530#pid51530
If connected to the GPIO of these reclockers, ProtoDAC will only receive 3.3V and not the required 5V power. This may result in ProtoDAC producing no sound or degraded sound. Here are two options to remedy this.
Option 1: Remove header pins 2 and 4 from the ProtoDAC GPIO prior to soldering so it no longer receives power from the reclocker GPIO, then use the GND and 5V solder pads between the RCA jacks on the ProtoDAC to power it with a 5V supply.
Option 2: This option leaves the ProtoDAC GPIO header unchanged by using a stacking header with pins 2 and 4 removed. Like option 1 the GND and 5V solder pads are used to power ProtoDAC with a 5V supply. If at a later point you want to attach ProtoDAC directly to a Raspberry Pi GPIO (which provides 5V) then simply remove the stacking header.
-
Test the connections after soldering the 40 pin header. Using a DMM, be sure there are no shorts between 5V power (pins 2 and 4) and ground (pin 6) and also 3.3V (pin 1). Consider not soldering pin 1 (or just remove pin 1 from the header), since it is unused. A short between 3.3V pin 1 and 5V pin 2 can damage the RPi. Finally, clean flux from the top of the PCB with flux remover.
-
Mount the three I2S resistors R1-R3 to the top of the PCB, and solder leads to the pads on the bottom.
-
Mount the module to the top of the PCB, and solder pins 1-3, 5, 6, 25 and 28 to the pads on the bottom.
-
Install capacitors C1, C2 or C5, C6 to the top of the board and use convenient pads (for example, an axial capacitor could use the left C5 pad for one lead and the right C2 pad for the other lead).
-
Install the I/V resistors R4 and R5 on the top with the labeled (pretty) sides facing away from the TDA1387 module for both, and solder leads to the bottom pads. Handle with care. Use the C1, C2, C5 or C6 capacitors to physically protect the resistors i.e. mount the resistors below the top of the capacitors. Use clip on heat sinks (alligator clips or test leads) to protect the resistors during soldering.
-
Install the RCA jacks to the top of the PCB and solder to the pads on the bottom.
-
Install electrolytic capacitors C3 and C4 to the top of the board and solder to the pads on the bottom. Be sure to double check the polarity.
Perform a final quality check and inspect all soldered joints for any obvious flaws or defects, such as cracks, gaps, discoloration, or excess solder. Finally, clean off any flux residue on the PCB.
Since the DAC is connected to the GPIO, any assembly errors could not only damage parts on the DAC, but could also permanently damage the Raspberry Pi. Pay particular attention to the polarity markings on the electrolytic capacitors C3 and C4.
The following sections contain the steps necessary to configure the ProtoDAC in moOde. Note The ProtoDAC does not have any configurable chip options, driver options or "hardware" volume and thus these settings will not be available in the configuration screens.
Click Menu, configure Audio to configure the I2S driver and Advanced Linux Sound Architecture (ALSA) output mode. The driver is configured in the "Audio Output" section. The output mode is configured in the "ALSA Options" section.
Select "ProtoDAC TDA1387 X8" from the "Named I2S device" dropdown list and then Restart the system. After restarting the "Volume type" setting should show "Software".
Select "Direct (hw)" from the "Output mode" dropdown list.
Click the "Home" button at the top left to return to Playback view. Set volume to a low level, scroll to the end of the Queue and click the Stereo Test track. Raise the volume to a suitable level and verify that the Left/Right channel and Phase tests produce correct results.
The ProtoDAC output polarity is inverted and thus a Polarity Inversion operation must be performed on the input signal so that correct +/- polarity is output to the loudspeakers.
Two polarity inversion options are included in moOde. The first is ALSA based which is available in the Music Player Daemon (MPD) section of the Audio Configuration screen. The second is CamillaDSP based which is available in the CamillaDSP Configuration screen.
- Menu, configure Audio
- Scroll down to the "MPD Options" section
- Scroll down to "DSP options"
- Turn "Polarity inversion" on
This assumes at least CamillaDSP version 2.0.1 and the sample configs have been updated to version 2. The "V2-ProtoDAC" configuration used here has the following description: ProtoDAC TDA1387 X8 Non-oversampling DAC. Invert +/- signal polarity on both channels and apply Flat dither to 16 bit samples.
- Menu, Configure, CamillaDSP
- Turn "Default device" on
- Set "Signal processing" to V2-ProtoDAC
- Click SAVE
Playback at the native bitrate of the source audio is recommended but sometimes if specific types of distortion are audible, resampling to a higher bitrate can be used to help reduce this distortion.
One type of distortion that may be reduced by resampling is Intermodulation (IM) distortion. IM distortion is caused by the presence of ultrasonic sample images. Resampling to 384 kHz will push these ultrasonic images past 192 kHz at which IM distortion would likely be inaudible.
Another type of distortion that may be reduced by resampling is band-edge response droop which is commonly referred to as "sinc droop". This typically occurs at 20 kHz but may also occur with greatly reduced effect in lower bands.
The ProtoDAC supports sample rates from 44.1 kHz to 384 kHz and accepts bit-depths from 16 to 32 bits where the Least Significant Bits (LSB) over 16 are ignored.
Two resampling options are included in moOde. The first is Sound eXchange (SoX) based which is available in the MPD Configuration screen. The second is CamillaDSP based which is available in the CamillaDSP Pipeline Editor screen.
- Menu, Configure, MPD
- Set Enable to "Yes"
- Set Bit depth to "Any" or optionally to "16" if you want SoX to manage bit depth conversion instead of ProtoDAC. In this case set "Default device" to OFF in CamillaDSP Config otherwise the bit depth will default to the highest bit depth reported by ProtoDAC which is 24-bit.
- Set Sample rate to the desired rate up to 384 kHz
- Leave Channels set to "Stereo"
- Leave Quality set to "High (Default)"
- Click SAVE
- Menu, Configure, CamillaDSP
- Set Signal processing to "V2-ProtoDAC"
- SAVE
- Scroll down to the Pipeline editor section
- Set Status to "ON"
- Set Expert mode to "ON"
- Click OPEN
- Click the Devices tab
- Set samplerate to the desired rate
- Set resampler_type to "AsyncSinc"
- Set profile to "Balanced"
- Set capture_samplerate" to "Default"
- Set Playback Bit depth to to "16" if you want CamillaDSP to manage bit depth conversion instead of ProtoDAC. In this case set "Default device" to OFF in CamillaDSP Config otherwise the bit depth will default to the highest bit depth reported by ProtoDAC which is 24-bit.
- Click "Apply and save" to save the settings to the configuration file
The following are questions received from a ProtoDAC builder (with answers):
The header (plastic piece) mounts on the bottom of the PCB. The pins are soldered on top (labeled ProtoDAC TDA1387 X8).
2. You said "and then do your best job on the working GPIO pins (2,4,6,12,35,40)”. Does that mean I only solder those pins that you mentioned?
It is best to solder all of the pins for good mechanical support. Just be sure to do your best solder job on the working pins.
Yes, that is correct. The square pad is pin 1.
I personally think that two black Panasonic FR-A sound best. Some people like the Nichicon UKA. The total capacitance of the parallel capacitors C3 and C4 should be 2000uF . If you use the blue Nichicon UKA 1000uF, use it with a black Panasonic 1000uF. Later on, feel free to experiment with other capacitors with larger or smaller capacitance. It does affect the sound quite a bit.
5. When I was looking for the capacitors, "voltage rating?" was one of the questions been asked? How do I choose the correct one?
For the output film capacitors, get the lowest voltage (probably 35V). The most voltage they could possibly see is 5V. The lower the voltage, the smaller the capacitor.
For the electrolytic capacitors (the black Panasonic or blue Nichicon), they should be rated no lower than 6.3V. They see the power supply voltage of 5V, and you need a safety margin. Again, the higher the voltage rating, the larger the capacitor for a given capacitance.
6. What is the purpose to have output capacitors? instant high current (low impedance), or the last step to filter out DC offset?
They are needed to block DC voltage at the output.
The PCB is grounded through GPIO pins 6 and 14 when it is attached to the Raspberry Pi. There is also a ground pad between the RCA jacks, labeled GND.
It is possible to power ProtoDAC and the Raspberry Pi by applying power to the 5V and GND pads between the RCA jacks on ProtoDAC. Note that this bypasses protection circuitry built into the Raspberry Pi, and thus any failures in ProtoDAC can potentially damage the Raspberry Pi.
| Designator | Description |
|---|---|
| C | Capacitor |
| H | Header |
| J | Connector |
| R | Resistor |
| U | Integrated Circuit (IC) |
| Acronym | Description |
|---|---|
| ALSA | Advanced Linux Sound Architecture |
| BCK | Bit Clock |
| CAD | Computer Aided Design |
| DAC | Digital to Audio Converter |
| DOUT | Data Output |
| DSP | Digital Signal Processing |
| GND | Ground |
| GPIO | General Purpose Input Output |
| HAT | Hardware Attached on Top |
| I2C | Inter-Integrated Circuit |
| I2S | Integrated Interchip Sound |
| IC | Integrated Circuit |
| I/V | Current to Voltage |
| kHz | Kilohertz |
| LSB | Least Significant Bits |
| MPD | Music Player Daemon |
| NOS | Non-Oversampling |
| PCB | Printed Circuit Board |
| SoX | Sound eXchange |
| uF | Microfarad |
| Vcc | Supply Voltage |
| VDC | Volts Direct Current |
| WS (LRCK) | Word Select (Left/Right Clock) |
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.