I don't know Holo's design decisions.... But mine was made based on what I believe would sound best, not the THD mesurements at full signal level....
You're right maybe they did optimize for measurements; I don't know and I'm not really concerned.... I trust that dam1021 has a great architecture and I know it has a nice sound
Do let us know what you think about the calibration method though. It seems pretty clear to me that better matching = better sound and better measurements. On a different note, do you know if the SPDIF and COAX input circuit would stop drawing current if no input is present or if the input selection is I2S? Also would there be an imbalance in the two channels if I only use the power on one board to power the input circuits? I had a PCB made last year that takes an external 3.3V and regulates it with LM1117 to 1.2V but it ended up drawing too much current even at idle.. or maybe I screwed up the circuit. Either way maybe taking power from the board is the better route..?
soren there is one problem I have observed in the latest dam102 i think i purchased v4. Without connecting any signal to either i2s or optical or spdif or usb whatever just leaving the entire header free and powering up the dac with regulators im getting hissing and sort of very low level pop. The signal is getting locked and sound is not clean what could be wrong? I have purchased 3 dam boards and two of them have same problem. How do I solve it?
You're right maybe they did optimize for measurements; I don't know and I'm not really concerned.... I trust that dam1021 has a great architecture and I know it has a nice sound
As I said, I didn't find it worthwhile or necessary when using a sign magnitude architecture.
Sorry, I have no clue what you mean.
I have never observed something like that.... a dam1021 shouldn't lock without a solid signal.
I see. But sign magnitude doesn't help the bit errors only zero crossing right?...
Does drawing power from one board to provide SPDIF signal for both boards possibly cause imbalances between the two boards? I can't just short the 1.2V and 3.3V on two boards right....
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As I said, please read up on, and understand the sign magnitude principle.
I have a little tech note on my website at:
Soekris Engineering ApS, Products
Don't see any problems there, the power supplies are regulated. And no, you can't just short regulators...
That's a great explanatory note. I didn't realize that industrial DACs cannot take advantage of sign-magnitude. This would explain the relative inferiority of industrial R2R chips used in audio. (PCM1704 is sign-magnitude though I think... anyways) But regardless of linearity at low levels, calibrated/compensated resistor arrays would reduce distortion at all levels right?... And since it's only software perhaps it can be done at relatively low cost and greater flexibility, i.e. something that can be toggled off. Does that make sense?...
I mean to say that even when I give the signal via I2s amanero its locking but still that noise is there.
One more question. Would it compromise the I2S isolation design and contaminate signal ground if I use the same power source to power both the isolation chip and the SPDIF input circuits, i.e. GND and ISO GND both connected to external power source GND? Even though only one of I2S and SPDIF would be working at a time, presumably
Alternatively, I can take only 3.3V from external power source and hope that it's close to 3.3V relative to signal GND for the purposes of powering SPDIF input circuit?
Alternatively, I can take only 3.3V from external power source and hope that it's close to 3.3V relative to signal GND for the purposes of powering SPDIF input circuit?
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Industrial DACs are more about absolute precision, while the Sign Magnitude principle only really matters for Audio, and yes, the PCM1704 was the last Burr-Brown (later TI) Sign Magnitude DAC, too expensive to manufacture, so it got EOL'ed....
You can calibrate at any level, but more precision require more precise AD converter and more bits to store the results.... And you need to have the ADC onboard as you would need to calibrate at each power up.
A Sign Magnitude converter isn't that critical with absolute precision, we sell plenty of dam1021 uing 0.05% parts and they sound good anyway.
Right. But why not just do a "factory calibration"? Monitors get factory calibrated with good results, even though color accuracy drifts non-negligibly over time. Still, it's worthwhile and done by the better manufacturers. Also, perhaps it's possible to allow user calibration using specific high quality ADC/AP to battle aging etc.? It seems a very interesting possibility to me.
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If no off-the-shelf AP can do the job on its own, maybe a "Soekris DAC calibrator" would sell well on the market. Again similar to how professionals buy expensive colorimeters to tune their monitors every now and then.
Also, did you see my last post...? I'm trying to fix my SPDIF input helper board but not quite sure about the GND connections...
Also, did you see my last post...? I'm trying to fix my SPDIF input helper board but not quite sure about the GND connections...
Seeing that TOSLINK receiver takes 3-5V and LM1117-1.2 has a wide range of operating input voltage, maybe it's feasible to only take 3.3V from the external power source and take signal and GND from dam1021. The external power source 3.3V and GND are also connected to ISO 3.3V and ISO GND. Would this prevent the noise in isolation circuit from entering the clean side?
Also, the TOSLINK receiver has an additional recommended 30pF between GND and Vout. Would it be objectionable to implement it? I'm paralleling two dam1021 with the SPDIF input circuit so according to Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz I probably should leave out the 330R. I'll keep the pads for the resistor on the PCB just in case. Does this sound like a reasonable implementation? Thanks so much!
Also, the TOSLINK receiver has an additional recommended 30pF between GND and Vout. Would it be objectionable to implement it? I'm paralleling two dam1021 with the SPDIF input circuit so according to Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz I probably should leave out the 330R. I'll keep the pads for the resistor on the PCB just in case. Does this sound like a reasonable implementation? Thanks so much!
@soekris I'm a bit confused about coax transformer selection. In the implementation thread it says that you recommended PE-65612NL. But does it work at the 192Khz that dam1021 supports up to? Is DA101C a better choice? I can grab a couple of the latter if it means a higher sampling rate. Thanks!
Decided to use external 3.3V, leave external GND disconnected and connect input board GND to SPDIF GND. The external 3.3V is similarly regulated as the onboard 3.3V. Plus, the TOSLINK receiver takes 3-5V, and LD1117-1.2 takes an even wider range of Vin. I don't see how there can be power instabilities... Only concern is when I2S is in use, whether the noise would leak into the clean side via 3.3V -> idle SPDIF circuit -> SPDIF signal and GND (the 0.1uF between 3.3V and GND might just allow all HF noise to flow right through?). The 3.3V GND is floating and connected to Amanero GND, so 3.3V may carry the noise as well. I'll test it next week, but any comments?...
EDIT: maybe I can use the 5V in the AZ Lite kit instead that's probably isolated from the 3.3V used for the isolation chip? Hmmm....
EDIT2: Unlikely that they're perfectly isolated but maybe better than using 3.3V directly... Plus 5V has more current capacity...From the manual:
EDIT3: reading the datasheet of ADP151 (used in AZ Lite kit), I shouldn't have used LD1117...
EDIT: maybe I can use the 5V in the AZ Lite kit instead that's probably isolated from the 3.3V used for the isolation chip? Hmmm....
EDIT2: Unlikely that they're perfectly isolated but maybe better than using 3.3V directly... Plus 5V has more current capacity...From the manual:
EDIT3: reading the datasheet of ADP151 (used in AZ Lite kit), I shouldn't have used LD1117...
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It's a little confusing, all your posts. But just connect all dam1021 GND's together and all the isolated GND's together too. They each need to be connected together so the signals have the same GND reference.
You can use any transformer designed for SPDIF audio.