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Improving a cheap chinese PCM1794 DAC
Improving a cheap chinese PCM1794 DAC
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Old 14th January 2019, 04:09 AM   #21
dreamth is online now dreamth  United Kingdom
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So it's not audible at all...Thank you! I still fear using 200nf capacitor to ground on I output as i have only one tda1543 at my disposal...
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Old 14th January 2019, 04:15 AM   #22
abraxalito is offline abraxalito  United Kingdom
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It could be audible if you don't choose a low enough noise opamp for the I/V. Subjectively when AD8017 is used for I/V the music is noisier without the filter than with. The noise I'm hearing when no filter's in circuit must be IMD, its not there when paused.

You have no need to worry about 200nF on your TDA1543's output, they're current sources inside and happily drive into an AC short circuit.
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Old 14th January 2019, 04:16 AM   #23
dreamth is online now dreamth  United Kingdom
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I just had a quick look to ad815 and 8017 datasheet and they seem to have huge slew rates, just like my tpa6120 (ths-fails).Do you need this filter to tame the dac or to compensate your i/v op-amps or both?I remember the article writen by Walt Jung on AD811 as i/v and he clearly mentioned that it needs a filter on the input or a compensation as it gets to oscillate easily.

Last edited by dreamth; 14th January 2019 at 04:20 AM.
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Old 14th January 2019, 04:21 AM   #24
abraxalito is offline abraxalito  United Kingdom
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I need the filter to (subjectively) enjoy the music. Unlistenable with AD8017 and no filter now. The only opamp I can listen to now without any filter is AD811.
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Old 14th January 2019, 04:25 AM   #25
dreamth is online now dreamth  United Kingdom
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Quote:
Originally Posted by abraxalito View Post
Unlistenable with AD8017 and no filter now.
What exactly do you mean by that?
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Old 14th January 2019, 04:25 AM   #26
Markw4 is online now Markw4  United States
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Quote:
Originally Posted by abraxalito View Post
I read of a very interesting comparison over on PTA a couple of days ago.
Very interesting. I noticed the same thing they described about DAC-3 and a lack of audibility or reduced audibility of low level reverb tails and ambiance. I noticed them more clear and present in Allo Katana dac when running it from linear supplies supplemented with film caps on the +-15v rails. I also hear the same low level reverb details with my modded dac during periods of time I was able to get jitter as low I ever was able to get it.

According to Allo, Katana measured lower in jitter than DAC-3 during tests performed by ASR. Katana, being a master mode dac, measured the lowest jitter ASR has found so far, according to Allo. That's a large part of the reason I am still working on reducing jitter.

Katana has ASRC and DPLL turned off, but my modded dac and DAC-3 has them turned on. I did have DPLL bandwidth adjusted to a very low value that I was able to keep stabilized for short periods of time.

Another thing I noticed is that when jitter is as low as possible on my modded dac and in normal operation of Katana dac that low level cymbal sound details approach more closely the almost perfect low level details of that sound exhibited by DAC-3.

Since I was using Katana with the 'thd' output stage, it did not have a pre I/V stage filter, nor does my modded dac. In contrast, I read somewhere that the designer of DAC-3 said there should be a filter cap before the I/V stages to filter out dac noise before the opamps. Unfortunately, I never saw a quote or blog of designer directly, so it was at best hearsay information.

Unfortunately, I did not have a dac to compare that I would consider to have a soft or warm sound. DAC-3 sounds less bright than both of the Q2M dacs I compared with it, but brightness does seem to fall off somewhat with improved jitter (per given interpolation filter). Most likely, the less bright sound of DAC-3 was mostly due to the proprietary external interpolation filter.

Lastly, I have heard what some would describe as hard and fast, or maybe cold and hard, sounding gear. I would not put DAC-3 in that class, but none of the Sabre dacs I have heard would be considered warm. I suspect that sound quality characteristic is related to its harmonic distortion profile acting on complex music signals to produce IMD. THD of the Sabre dac chips is rated down around -120dB (presumably with distortion compensation of H2 and H3 enabled). Some people don't believe distortion down at that level can be audible, but in my experience I believe it can be.

Last edited by Markw4; 14th January 2019 at 04:41 AM.
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Old 14th January 2019, 06:04 AM   #27
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by dreamth View Post
What exactly do you mean by that?
I mean that there's zero desire to listen to the unfiltered AD8017-based DAC. I always want to put the filter back in, without its just too unmusical.
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Old 14th January 2019, 02:48 PM   #28
pachy is offline pachy  Bulgaria
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Hey, thanks for the interesting discussion. I have chosen the PCM1794 after I read this article, which has in depth measurement/analysis/comparison of delta-sigma/multibit DACs and their differences. You may find it interesting: Какой звуковой ЦАП лучше? — Меандр — занимательная электроника. It is in russian so you should probably use Google Translate.

By the way, here is the whole setup in a temporary enclosure out of a Polo RL scarf until I find someone with a CNC nice enough to make me two simillar enclosures.

Click the image to open in full size.

The setup consists of:
- A DIY AC filter
- 2x15VAC+2x9VAC R-Core transformer feeding the DAC board
- 2x7,5VAC feeding the XMOS reclock and Raspberry Pi
- Raspberry Pi 3 running Volumio fed by a LT1083 + CRC filter PSU(on the black prototype PCB, painted black with a spray can)
- JLSounds XMOS, with it's reclock after galvanic barrier fed by an LM317 + CRC PSU(also on the black board)
- The modified chinese PCM1794 board
- An LCD display+MCU+rotary switch that came with the chinese board used to switch digital inputs and display current signal frequency

While still burning in, the sound of the PCM1794 is amazing. TBH I have never expected such a detailed sound that is still warm and pleasant to listen to from a delta-sigma DAC except for the most expensive Sabre pros. I don't believe the TDA1541 myths anymore.

The good thing is that the whole streamer/DAC costed less than 250$ including the trafos, raspberry, xmos, memory card, DAC board and all the components for the upgrade. It allows me to listen to music from online streaming services such as Spotify and Tidal, local HDD and I can still switch to the toslink coming from my TV with one click and use the DAC for Xbox(pass-through) and Netflix.

I still have to add the IR receiver for an Apple remote I have laying around but Volumio has a web interface so it's not mandatory.
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Old 14th January 2019, 03:12 PM   #29
dreamth is online now dreamth  United Kingdom
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I had similar perceptions of "unmusical" devices with the most linear and non-oscillating ones...or with preamplifiers that had very low impedance feedback networks or filters in the path of a signal showing less perceivable noise.

The measurements on a scope showed nothing different in two different passive riaa networks up to 20khz square wave signals for an audio application i want to show you.

You have a similar statement of mine at the end of this post :
UNU-pnono riaa mm preamp


I built a device these days and I have a similar problem with the break point of a chosen rc network where i can't easily make a choice between a noisier, but less aggressive with the highs content, opposed to a more effective network at cutting the highs.You can see here what is all about:

Best way to mod cheap cd-players-enhancing the noise



It seems that either the instability or the noise is preferable to our ears too.I realized that after a famous now video on youtube where a guy showed 4 or 5 versions of the same Pink Floyd album recordings and the reel to reel tape was preferred by most people and i personally think that was just because of the high content of noise on tape, not because it was a more accurate recording than the others.

Last edited by dreamth; 14th January 2019 at 03:15 PM.
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