ProtoDAC TDA1387 X8 project

[wolf7250]

I have been down a bit of a rabbit hole. Wanted to share some of this to see what you think and also on the off chance it would help.

Been doing quite a bit of reading and watching videos on Audio Science Review and Amir seems quite convinced that RPi noise etc has no impact on the noise and quality of output from a USB DAC Do USB Filters Make DACs Sound Better? He also has done some analysis as to whether Linear Power Supplies make a difference here Do you need linear power supply for DACs?

This has also led me to a website called Archimago's Musings where he also supports this: MEASUREMENTS: Raspberry Pi 3 as USB Audio Streamer (with recommended CRAAP config & TIDAL/MQA arrives).

Now I know that this is all related to USB DACs, but he (Archimago) also did an analysis of the HiFiBerry DAC+ Pro with a SMPS PSU vs a battery PSU. There was no difference in any of his tests between these two power options. And the HiFiBerry with a standard SMPS power supply performed just as well as high end DACs. MEASUREMENTS: Raspberry Pi 3 & HiFiBerry DAC+ Pro (Audio Streaming).

@hifinet you use a RPi Zero W with an Allo Kali reclocker and the ProtoDAC correct? Are you happy with the output from this setup?


My readings are really making me consider going with just a RPi 3B+/3A+ -> FiFoPi MA -> ProtoDAC. I was considering getting an IsolatorPi from Ian Canada as well for galvanic isolation. But I just don't know that this is needed (and frankly I just don't want to spend money if I don't need to). Especially given Archimago's findings with the HiFiBerry DAC+ Pro which didn't have any galvanic isolation.

Interested in comments and if any of the links above help anyone else then great  .

[hifinet]

ProtoDAC is NOS (nonoversampling) and it also does not have an output filter. The frequency response graph would look similar to the Pono Player. However, I think you would only experience the high frequency roll off (called the sync droop) if you can hear over 22.05kHz (for 44.1kHz recordings).  Using a sharp reconstruction filter with a corner frequency of 22.05kHz there would be no sync droop. This seems very counterintuitive.  Just like the other DACs with oversampling. Wouldn't normal human hearing provide for an adequate reconstruction filter? If the sample rate was 48kHz, you would need hearing > 24kHz to appreciate the sync droop. Subjectively, I have not been able to hear the sync droop. ProtoDAC does not seem to have rolled off high frequencies, but I am old and my hearing is no where near normal.

My own experience with power supplies. The Allo 5V 3A SMPS is clearly noisier subjectively than the 5V ultracapacitor supply in the PurePi.

[hifinet]

There is a difference with a multibit DAC like the TDA1387 in ProtoDAC and a Delta Sigma DAC. There might be a much greater dependence on the power supply quality with a multibit DAC. From my experience and others, the power supply makes a big difference in the sound quality of ProtoDAC.

[wolf7250]

Could it be that DACs like the HiFiBerry DAC+ Pro have a Ultra-low-noise linear voltage regulator (or similar in the case of USB DACs) and the ProtoDAC doesn't and that could be making a difference? (apologies if the ProtoDAC does have something similar, put that down to a lack of understanding of the specs)

[wolf7250]

Apologies, I didn't refresh the page and you had already answered/responded to my previous question.
OK. So it seems as though with the ProtoDAC improvements will be seen through having either a SMPS with noise filtering or a low noise PSU, an IsolatorPi (to remove galvanic noise) and a FiFoPi MA to reclock.

[Tim Curtis]

@wolf7250, a good approach with the ProtoDAC is to just build one, put it right on top of a Raspberry Pi, use a good quality SMPS power supply and start listening to your favorite music. its as low cost as it gets.

Then experiment with reclockers, other power supples, cap rolling etc and see what happens. Its the essence and beauty of DIY :-)

[hifinet]

Excellent advice, Tim.

ProtoDAC is simple and no on-board voltage regulators, so it is very dependent on the power supply. I have used linear supplies, various SMPS, LiPO with LT1963, ultracap supply. They all sound different in terms of noise, bass, dynamics and soundstage.  Describing sound is metaphorical and imprecise. Personal taste and music is different. In the end, experiencing the options for yourself is often the only way you can really know.

A ProtoDAC customer recently told me that he is using a beefy 12V linear power supply with a 5V LT1963 (this with a DIR9001 SPDIF to I2S board as a CD DAC), and it sounds very close to his Audio Note AD1865 tube DAC. Link

[wolf7250]

Agreed. Thanks @Tim Curtis and @hifinet.

This is absolutely spot on. I have been approaching this project as something that needs to be done 'right' from the beginning or else I have failed (or wasted money).
A quirk of my personality I suppose.
And I have gotten very hung up on the definition of 'right'.

I think I will take your advice @Tim Curtis and just start with the ProtoDAC on top of a Raspberry Pi and then go from there and keep learning along the way.

[OnkelPH]

Agreed. Thanks @Tim Curtis and @hifinet.

This is absolutely spot on. I have been approaching this project as something that needs to be done 'right' from the beginning or else I have failed (or wasted money).
A quirk of my personality I suppose.
And I have gotten very hung up on the definition of 'right'.

I think I will take your advice @Tim Curtis and just start with the ProtoDAC on top of a Raspberry Pi and then go from there and keep learning along the way.

I'm using ths regulator inspired by Gabster, Cheap way of getting low noice power. A 5vdc for the ProtoDAC is no in the making.
I'm also using pinconnectors on my board for easy swap out capasitors and other parts that i want to upgrade.                 

[hifinet]

What are your plans for the 5V ProtoDAC supply?

The low noise 3.3V adjustable supply uses the LM317 regulator. There are many different ways of lowering the noise of the LM317, by adding a cap on the adjust pin or active circuits (D noizinator). I am not sure exactly how they are doing it on that board yet. Usually to get low noise from the LM317, you sacrifice transient response. That's fine for powering the Q7, which probably has relatively constant current requirements.