Why NOT to use these DACs for audio ?

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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
 
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 ?
 
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.
 
tritosine said:
yeah and with 2nV of glitch its anything but classic :clown:

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:
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....


thats hardly an argument against it when the purpose is solely personal/diy/hobby. lets ignore cost for now.

zilym said:
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?
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:
Instead, why not wire up a set of hand selected, matching resistors in R2R fashion against a cheap 16-bit microcontroller?
To be honest, I have considerd that.
 
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.
 
percy said:


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.


When you find a SPDIF rx with SPI and straight binary, do let us know.
 
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