So I ran into this list of R2R DACs from TI that have very good INL and DNL specs. They are not typical 'audio' dacs but they are still afterall a classic r2r dac. I'd imagine they would be the NOS DAC builder's dream dacs?! Or even os dacs following an oversampling filter or asrc, for the matter of fact.
But I have never seen any mention of these types of dacs around here. Am I missing anything ? Do you see any reasons why these dacs cannot be used for audio purposes ?
Some of them are -
DAC8811/2
DAC8830
DAC8871
But I have never seen any mention of these types of dacs around here. Am I missing anything ? Do you see any reasons why these dacs cannot be used for audio purposes ?
Some of them are -
DAC8811/2
DAC8830
DAC8871
I have not looked at these specific DAC's, but in general non-audio DAC's will not work. Audio DAC's have input sections for decoding standard audio data streams like I2S. Sometimes there are also issues with linearity and resolution.
-David
-David
All those dacs have standard serial interfaces. Are you aware of any spdif receivers that do not have a serial interface output ?
And what "issues with linearity and resolution" are you talking about exactly when a 16bit dac has ±0.5LSB DNL and ±1LSB INL and 16bit monotonicity ?
And what "issues with linearity and resolution" are you talking about exactly when a 16bit dac has ±0.5LSB DNL and ±1LSB INL and 16bit monotonicity ?
doubt these are classic r2r dac-s , once we suppose a classic r2r dac has glitch . Looks like you only look at the numbers. These arent even I out or i cant find specs?
tritosine said:
DAC8871, for example, has output impedance specified (having voltage rather current output).
I looked at those R2R DAC's a long time ago and decided against using them because of how much they cost (>$13 each). Since they only provide one channel each, you have to buy two of them to get stereo audio. That suddenly prices these parts beyond high end audio DAC chips, while limiting you to only 16-bit audio. Then the question becomes, why would you want to use these DAC chips for audio when audio DACs can do more for less?
hifimaker has a point that these chips do not implement support for standard I2S audio streams. These use something more like an SPI interface, which could probably be hacked into accepting I2S audio by having some supporting logic chips or a microcontroller to arbitrate data signals. But at this point, why bother?
Instead, why not wire up a set of hand selected, matching resistors in R2R fashion against a cheap 16-bit microcontroller? Resistors are super cheap and you can buy a pair of PIC24FJ64GA004 16-bit microcontrollers for way less than a pair of those TI R2R DAC chips. Plus you've got some room for extra features, like re-clocking internally, etc.
Another idea I'd like to see someone try is using a microcontroller with a ton of PWM outputs like dsPIC33FJ64GP206 in a PWM/Resistor Hybrid DAC configuration. In theory, with enough PWM pins and properly selected resistors, this design could achieve greater bits of resolution while using fewer components. I did it using two PWM pins per channel to get to 16-bit audio, but never had time to try anything further.
I was using a clock source that was not an exact multiple of the audio playback frequency. I think that resulted in muddy high frequency sounds. I would definitely try to use a clock source that is a perfect multiple of the audio playback frequency if I were to try this stuff again.
hifimaker has a point that these chips do not implement support for standard I2S audio streams. These use something more like an SPI interface, which could probably be hacked into accepting I2S audio by having some supporting logic chips or a microcontroller to arbitrate data signals. But at this point, why bother?
Instead, why not wire up a set of hand selected, matching resistors in R2R fashion against a cheap 16-bit microcontroller? Resistors are super cheap and you can buy a pair of PIC24FJ64GA004 16-bit microcontrollers for way less than a pair of those TI R2R DAC chips. Plus you've got some room for extra features, like re-clocking internally, etc.
Another idea I'd like to see someone try is using a microcontroller with a ton of PWM outputs like dsPIC33FJ64GP206 in a PWM/Resistor Hybrid DAC configuration. In theory, with enough PWM pins and properly selected resistors, this design could achieve greater bits of resolution while using fewer components. I did it using two PWM pins per channel to get to 16-bit audio, but never had time to try anything further.
I was using a clock source that was not an exact multiple of the audio playback frequency. I think that resulted in muddy high frequency sounds. I would definitely try to use a clock source that is a perfect multiple of the audio playback frequency if I were to try this stuff again.
tritosine said:yeah and with 2nV of glitch its anything but classic
but you realize that the glitch is only a 'carry over' glitch - i.e. only when the input code changes from 32767 to 32768 and vice versa, right ?
zilym said:
thats hardly an argument against it when the purpose is solely personal/diy/hobby. lets ignore cost for now.
why complicate it ? unless you are talking about slaving the source via i2s, I see no point in using an i2s connection. I'd rather rely on my own clock than on the one coming over an i2s from 'xyz' source. And with jitter rejection abilities of an spdif receiver like that of the wm8804, spdif to spi becomes even more viable.zilym said:
To be honest, I have considerd that.zilym said:
ultra low glitch is a feature and definately not in a "classic" way. Perhaps invest some time and read what they mean with "segmented" architecture.
rfbrw,
at this point its more of a concept than a design. A feasibility study so to speak. Those chips that I listed in my original post are just examples. I am sure there are similar products from other manufacturers.
I want to find an argument convincing enough to scare the idea of this dac out of my mind.
The idea is simple - use the 3-wire/serial interface from the spdif receiver to such a dac. Thats it. That essentially gives you a nos dac.
I believe oversampling filters like the npc sm5842/7 also have serial input/output so you could put that filter in the middle and make an 8x oversampling dac.
at this point its more of a concept than a design. A feasibility study so to speak. Those chips that I listed in my original post are just examples. I am sure there are similar products from other manufacturers.
I want to find an argument convincing enough to scare the idea of this dac out of my mind.
The idea is simple - use the 3-wire/serial interface from the spdif receiver to such a dac. Thats it. That essentially gives you a nos dac.
I believe oversampling filters like the npc sm5842/7 also have serial input/output so you could put that filter in the middle and make an 8x oversampling dac.
"I want to find an argument convincing enough to scare the idea of this dac out of my mind."
small geometry ?
If you try and succeed getting some unpackaged "classic" r2r die, now that would be interesting ( plastic packaging hurts laser trim >14bit level and degrades time stability).
small geometry ?
If you try and succeed getting some unpackaged "classic" r2r die, now that would be interesting ( plastic packaging hurts laser trim >14bit level and degrades time stability).
Ok I see what you're saying. The serial interface is only for 'control' and not for 'data'. You also made a point about the binary data type.
Looks like this is going to become a 'microcontroller' project then 😉
Looks like this is going to become a 'microcontroller' project then 😉
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