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Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
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Old 24th July 2014, 12:17 PM   #91
Kastor L is offline Kastor L  Europe
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LME49724 looks nice!

0.02% resistor alternative with Silver design and zero EMI? - Take this DAC to the heavens -

"Firstly, nickel limits the working temperature to 160°C and tin has a peak temperature of 230°C. Therefore, by using an inner terminal made from silver/palladium and an outer terminal of platinum/silver, Riedon is able to offer devices that operate up to 300°C. Nickel is also magnetic, so resistors with nickel/tin terminals cannot be used in applications such as magnetic resonance imaging (MRI) where there are strong magnetic fields."

Link --- digikey.com/en/articles/techzone/2013/sep/power-rating-is-just-one-resistor-parameter-to-consider
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Last edited by Kastor L; 24th July 2014 at 12:21 PM.
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Old 24th July 2014, 01:01 PM   #92
doctormord is offline doctormord  Germany
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Quote:
Originally Posted by soekris View Post

Don't really understand what you mean there, but no need for anything, there is just a simple capacitor at the output of the DAC's resistor chain, making a 270 Khz Bessel low pas filter.
I mean compensation of capacitive resistance caused by stray capacitance. When I.e. switching at 3Mhz and 1pf stray capacitance this will render to 50kOhm capacitive resistance. This must be compensated somehow, otherwise the voltages at the netpoints aren't right.
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Old 24th July 2014, 01:16 PM   #93
soekris is offline soekris  Denmark
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Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
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Originally Posted by doctormord View Post
I mean compensation of capacitive resistance caused by stray capacitance. When I.e. switching at 3Mhz and 1pf stray capacitance this will render to 50kOhm capacitive resistance. This must be compensated somehow, otherwise the voltages at the netpoints aren't right.
No problem here, thanks to the very clean and compact SMT design and 4 layer PCB, any stray capacitance are too low to matter much. I even choose to use only 7 bit from each shift register, as the 8th bit are located on the other side of the chip...
And the 470 pF capacitor at the output of the R-2R resistor chain take care of anything coming though.

The results can be seen at the FFT plots, so clean....
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Old 24th July 2014, 01:22 PM   #94
HpW is offline HpW
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Originally Posted by soekris View Post
I decided on 28 bit, to have headroom for a perfect digital volume control..
How do you feed 28bit to the DAC?

Hp
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Old 24th July 2014, 01:30 PM   #95
HpW is offline HpW
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Originally Posted by soekris View Post
No problem here, thanks to the very clean and compact SMT design and 4 layer PCB, any stray capacitance are too low to matter much.
How low is your stray capacitance between your traces? In my old I/V DAC design some x pF have mattered.

Also take care after time, where some dirt comes over/between the soldering SMD's..

Quote:
Originally Posted by soekris View Post
The results can be seen at the FFT plots, so clean....
on your second given FFT plot, there are some spurious power harmonics...

Hp
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Old 24th July 2014, 01:44 PM   #96
esgigt is offline esgigt  Netherlands
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Originally Posted by HpW View Post
Also take care after time, where some dirt comes over/between the soldering SMD's..
If I understood Jean-Paul well, those connections ought to be insulated from the environment.
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Old 24th July 2014, 01:45 PM   #97
bmwparts is offline bmwparts  United States
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Originally Posted by HpW View Post
How do you feed 28bit to the DAC?

Hp
You don't, 28 bit means it has 4 bits of headroom for digital volume control that doesn't distort the signal. You still feed it a 24 bit signal.
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Old 24th July 2014, 01:55 PM   #98
esgigt is offline esgigt  Netherlands
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Originally Posted by Kastor L View Post
LME49724 looks nice!

0.02% resistor alternative with Silver design and zero EMI? - Take this DAC to the heavens -

"Firstly, nickel limits the working temperature to 160°C and tin has a peak temperature of 230°C. Therefore, by using an inner terminal made from silver/palladium and an outer terminal of platinum/silver, Riedon is able to offer devices that operate up to 300°C. Nickel is also magnetic, so resistors with nickel/tin terminals cannot be used in applications such as magnetic resonance imaging (MRI) where there are strong magnetic fields."

Link --- digikey.com/en/articles/techzone/2013/sep/power-rating-is-just-one-resistor-parameter-to-consider
Kastor, can you please explain to me the relevance, for this confuses me? In my opinion the DAC won't be operated in ambient temperatures higher than 50 Celsius... So I guess the temperatures of any component will not exceed 75 degrees.. So what's the need of components with much higher operating temperatures?
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Old 24th July 2014, 02:00 PM   #99
soekris is offline soekris  Denmark
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Reference DAC Module - Discrete R-2R Sign Magnitude 24 bit 384 Khz
Quote:
Originally Posted by HpW View Post
How low is your stray capacitance between your traces? In my old I/V DAC design some x pF have mattered.

Also take care after time, where some dirt comes over/between the soldering SMD's..

on your second given FFT plot, there are some spurious power harmonics...

Hp
Haven't calculated trace stray capacitance, just did my best to keep things separated at layout and have the analog signals on the top side, with digital signals to the shift registers on the bottom side.
Again, the advantage of the sign magnitude R-2R dac is that MSB bits are NOT switching when not used, so you don't have large signals straying into low levels analog signals. That's also why you don't need de-glitching on a sign magnitude DAC, there simply aren't any glitches....

Those "spurious power harmonics" are more than -140 db down and mostly likely from the EMU-0404, as my initial testing are powered from my lab power supply....

I also really need better test equipment, the choice seems to be between real audio analyzers starting at $10K, or inadequate low cost AD/DA boxes like the EMU-0404. Something in between are needed, that might be my next project :-)
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Old 24th July 2014, 03:04 PM   #100
Kastor L is offline Kastor L  Europe
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Originally Posted by esgigt View Post
Kastor, can you please explain to me the relevance, for this confuses me? In my opinion the DAC won't be operated in ambient temperatures higher than 50 Celsius... So I guess the temperatures of any component will not exceed 75 degrees.. So what's the need of components with much higher operating temperatures?
No relevance for temperature, only for EMI or Silver if you believe in Silver.

A transformer has EMI, R-core transformers have the least EMI. Silver has the least electrical resistance, the electron transmission is akin to a direct pathway.

If Silver and EMI are overkill, yes, very likely, but if the price is not an issue then it's an alternative.

I think soekris can use any resistors he desires, this is his project and we are his disciples, any resistor will still be perfect.
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