ProtoDAC TDA1387 X8 project

[kLOkUIS]

Hello everyone, I build this digital to analog converter and it also converted me… Thank you so much to @hifinet for this project! I knew a good converter made a difference in listening music, but not to this extend

This is such a wholesome project. Especially because it’s upgradable. I would recommend for audiophile novices to take on this project and to not start with all the greatest components and additions. I’m already enjoying mine so much in its configuration. Literally rediscovering music. And I can stay excited about it because the moment I get used to this listening experience I can try out another resistor, build a clean power source, add a ground wire , add a reclocker,…

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[kaffeereibn]

Quick question to the polarity setting in the audio settings:

If I enable that, since the ProtoDAC needs that setting it doesn't stick...
I can turn it on, but after refreshing the screen it is off again...

Try this fix.
https://moodeaudio.org/forum/showthread....8#pid49028

Thank you Tim!

[Tim Curtis]

Hello everyone, I build this digital to analog converter and it also converted me… Thank you so much to @hifinet for this project! I knew a good converter made a difference in listening music, but not to this extend

This is such a wholesome project. Especially because it’s upgradable. I would recommend for audiophile novices to take on this project and to not start with all the greatest components and additions. I’m already enjoying mine so much in its configuration. Literally rediscovering music. And I can stay excited about it because the moment I get used to this listening experience I can try out another resistor, build a clean power source, add a ground wire , add a reclocker,…

[img]<a href=[/img]" />[img]<a href=[/img]" />[img]<a href=[/img]" />[img]<a href=[/img]" />

Coolness. 

Is that copper shielding between the ProtoDAC and the Pi?

[hifinet]

I would recommend for audiophile novices to take on this project and to not start with all the greatest components and additions. I’m already enjoying mine so much in its configuration. Literally rediscovering music. And I can stay excited about it because the moment I get used to this listening experience I can try out another resistor, build a clean power source, add a ground wire , add a reclocker,…

Thank you for the kind words, and thank you for pointing this out. Very impressive custom chassis work on your build!

For anyone sitting on the fence about building this DAC, because you don't have much experience soldering, this is a very good beginner project. You don't need the expensive Z-foil I/V resistors, fancy power supplies or reclockers to appreciate the sound quality of this DAC. If soldering the GPIO header seems to be a daunting task, then just solder five jumper wires for power and I2S. The DAC will work at up to 384kHz sampling with simple, unshielded jumper wires. See the Gaspar74 build here for an example of using jumper wires. The rest of the soldering is minimal. The PCB is easy and inexpensive to obtain from JLCPCB, or other PCB manufacturers, using the Gerber files provided. Just upload the zip file and select the basic options.

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The first working prototype.

[kaffeereibn]

UPDATE:

I'm sorry, I found the mistake. I had as a Device setting "ProtoDAC" but I needed to set "HifiBerry DAC+ PRO per Ian Canadas manual.

Now it is working and I have to say I'm completely blown away..
I basically followed the video from "Gabster" for the DAC build.

The only thing left to do is to try the other (red) Caps, Mark sent me with the resistors and maybe add the PurePi power supply if I'm feeling rich. I'm not sure though if my ears can hear a power supply :-)

Hi kaffeereibn and hi all,
Very nice built but  I have a question: interesting the shield but I am afraid about the termal dissipation. What is the cpu temperature?
You can use the command :

Code:

moodeutl -m

to monitor it.
Best regards,
Francesco

Hi Francesco,
I'm not too concerned with CPU temp as the tasks at hand are not very challenging for a Raspberry 3B+ (And raspis can take a beating ;-))
After about one hour of operation (playing FLAC) the CPU temp reads 50.5 degC
BR
Martin

[kLOkUIS]

Hello everyone, I build this digital to analog converter and it also converted me… Thank you so much to @hifinet for this project! I knew a good converter made a difference in listening music, but not to this extend

This is such a wholesome project. Especially because it’s upgradable. I would recommend for audiophile novices to take on this project and to not start with all the greatest components and additions. I’m already enjoying mine so much in its configuration. Literally rediscovering music. And I can stay excited about it because the moment I get used to this listening experience I can try out another resistor, build a clean power source, add a ground wire , add a reclocker,…

Coolness. 

Is that copper shielding between the ProtoDAC and the Pi?

Yes, kinda. I thought it was copper, but my father pointed out it’s phosphor bronze. It apparently had the advantage that it keeps its Sheen for longer. Future will tell

[marco.mosca]

Yes, correct. The easiest way is to reverse speaker leads on both speakers.

Just finished assembly. It sounds really great! One of the best DAC I have ever listened.

@hifinet thanks for sharing this project.

Marco

[hifinet]

Correction to a previous post #122 regarding obtaining a balanced output from ProtoDAC:

"Use two TDA1387 X8 modules and a 74ACT86 logic IC. One module gets DATA (from I2S) and the other inverted DATA. The analog outputs will be 180 degrees out of phase." is not correct.

According to an explanation posted in diyAudio :

"The problem is that with binary arithmetic, there is a difference between inversion and negation.
Inversion is a logical operation that is applied the each bit individually. The rule for inversion is invert every bit.
Negation is an arithmetic operation and is applied to the value of the data represented by the collection of bits. The rule for negation is invert every bit and then add 1 to the resulting binary number.

When you invert the number 0, you get -1.
When you invert the number 1, you get -2.
And so on...This is not the behavior you want to create a balanced signal.

When you negate the number 0, you get 0.
When you negate the number 1, you get -1.
And so on...This is the behavior you want to create a balanced signal.

A problem with negation is that certain input can lead to binary overflow and the wrong result. Recognizing and correcting overflow with a hardware implementation is not simple, but is easy with software.

You should also know there is no value in using a pair of DACs to create a balanced signal, even if you do the proper negation of the input. One DAC will be converting a positive number while the other is converting a negative number. It is unlikely the two DACs will be sufficient matched to make it worthwhile."

"...inverting the data introduces an undesirable offset. It's better to use a transformer to create the balanced signal from the single-ended output of the DAC chip."

[Nutul]

Correction to a previous post #122 regarding obtaining a balanced output from ProtoDAC:

"Use two TDA1387 X8 modules and a 74ACT86 logic IC. One module gets DATA (from I2S) and the other inverted DATA. The analog outputs will be 180 degrees out of phase." is not correct.

According to an explanation posted in diyAudio :

"The problem is that with binary arithmetic, there is a difference between inversion and negation.
Inversion is a logical operation that is applied the each bit individually. The rule for inversion is invert every bit.
Negation is an arithmetic operation and is applied to the value of the data represented by the collection of bits. The rule for negation is invert every bit and then add 1 to the resulting binary number.

When you invert the number 0, you get -1.
When you invert the number 1, you get -2.
And so on...This is not the behavior you want to create a balanced signal.

When you negate the number 0, you get 0.
When you negate the number 1, you get -1.
And so on...This is the behavior you want to create a balanced signal.

A problem with negation is that certain input can lead to binary overflow and the wrong result. Recognizing and correcting overflow with a hardware implementation is not simple, but is easy with software.

You should also know there is no value in using a pair of DACs to create a balanced signal, even if you do the proper negation of the input. One DAC will be converting a positive number while the other is converting a negative number. It is unlikely the two DACs will be sufficient matched to make it worthwhile."

"...inverting the data introduces an undesirable offset. It's better to use a transformer to create the balanced signal from the single-ended output of the DAC chip."

Inverting digital values should not be treated bit-by-bit, IMO, but byte-byte, or better, word-by-word (being the word a 16, 24, 32 or 64 bit), in order to get a 0 from a 0, a -1 from a +1, and a -16384 from a + 16384, and so on...
Of course, I do not know the bits and bolts at a low level, but from a software POW (a PGA one?) this is the way to go. Single bits need a context, and a positive / negative value represent such context; you cannot treat them (negate / invert) alone.

[hifinet]

I have seen the technique of inverting individual bits to get polarity inversion in a few examples of diyAudio circuits. It may not give the perfect result, but it also might be "good enough" for audio. Any offset (DC) will be blocked from the output. For balanced output, one would still need to find two matched DACs, and since a transformer will give a nearly perfect result (with other advantages of a transformer), that seems to be the best solution for balanced output with ProtoDAC.