Staggered parallell units
I have looked at staggering units before, but came up short on the theory. My thinking was that this would constitute the equivalent of a low pass filter + that the spiking would be staggered as well.
So I looked at it some more -- what happened if I staggered by 1 MCLK? What happened if I modulated a set of four: 1 pause 2 in parallell pause 1 etc.
Clearly there is an optimal pattern. Who remembers enough of signal theory from school to set up an "optimal" pattern/sequencing/timing? I would guess that about 4-8 units in sequence is relatively practical, and I am assuming that staggering is a good thing.
Petter
I have looked at staggering units before, but came up short on the theory. My thinking was that this would constitute the equivalent of a low pass filter + that the spiking would be staggered as well.
So I looked at it some more -- what happened if I staggered by 1 MCLK? What happened if I modulated a set of four: 1 pause 2 in parallell pause 1 etc.
Clearly there is an optimal pattern. Who remembers enough of signal theory from school to set up an "optimal" pattern/sequencing/timing? I would guess that about 4-8 units in sequence is relatively practical, and I am assuming that staggering is a good thing.
Petter
sonnya said:
Sonny, this is current-output DAC, I think, just like the other modern and better-quality sigma-deltas. The voltage output of 9Vrms is at the post-amp, they specify it an case of the 1mA->1V conversion, I suppose.
BTW: Why in fact will I need 130dB of DR, I actually will be quite happy with 120dB, then it will be possible to arrange a quality, residual noise and distortion-free DIGITAL VOLUME COTROL. I dare if any human can hear more than 100dB of Dynamic Range without pain and hear-loosing
Best Regards to everyone
Direction of Currents
Petter,
I'm not sure if you are right with the bias currents you describe in your post ...
There seems to be some confusion about the direction of currents if you look at the AD1955 datasheet where it is stated " The AD1955 audio outputs sinks a current proportional to the input signal, superimposed on a steady bias current." This current is specified as -3.24 mA. This is where it goes wrong. If a current is sinked it is positive (from the DAC's perspective). AD recommends to compensate this current with a pull-up resistor to a positiv voltage.
Now if you look at the PCM1792 datasheet there is a specification for a center current of -6.2 mA at BPZ. I think TI has got the direction issue right which means the DAC sources a bias current. There is no recommendation from TI to do so but you can compensate this current with a pull-down to a negative voltage.
Is that right or have I mixed things up?
Best regards,
Norbert
Petter,
I'm not sure if you are right with the bias currents you describe in your post ...
There seems to be some confusion about the direction of currents if you look at the AD1955 datasheet where it is stated " The AD1955 audio outputs sinks a current proportional to the input signal, superimposed on a steady bias current." This current is specified as -3.24 mA. This is where it goes wrong. If a current is sinked it is positive (from the DAC's perspective). AD recommends to compensate this current with a pull-up resistor to a positiv voltage.
Now if you look at the PCM1792 datasheet there is a specification for a center current of -6.2 mA at BPZ. I think TI has got the direction issue right which means the DAC sources a bias current. There is no recommendation from TI to do so but you can compensate this current with a pull-down to a negative voltage.
Is that right or have I mixed things up?
Best regards,
Norbert
Norbert,
I know for a fact that the 1853 has a steady state current as well as a DC offset from which it lies. I don't know about the other Analog Devices chip. In their applicaiton note, this is "fixed" by the following op-amps (common mode input = zero output)
What is a bit painful is the DC levels at that point.
I am not going to argue with the Analog Devices application engineers who surely are a lot smarter and better versed in these issues than me (I know, I have spoken with one of them
), but it seems to me that if you place a pull up/down resistor at the output, you have essentially created the IV conversion at that point which as far as I know is a total no-no for current output DAC chips in the eyes of application engineers.
Regarding the PCM1792: Whether I got the current directions right or wrong is something that I was unable to be conclusive about from the datasheet. In my book, a source is a generator or driver if you wish, and a sink is a receiver. Thus I am in disagreement with you. I might very well be wrong though
Petter
I know for a fact that the 1853 has a steady state current as well as a DC offset from which it lies. I don't know about the other Analog Devices chip. In their applicaiton note, this is "fixed" by the following op-amps (common mode input = zero output)
What is a bit painful is the DC levels at that point.
I am not going to argue with the Analog Devices application engineers who surely are a lot smarter and better versed in these issues than me (I know, I have spoken with one of them
), but it seems to me that if you place a pull up/down resistor at the output, you have essentially created the IV conversion at that point which as far as I know is a total no-no for current output DAC chips in the eyes of application engineers.Regarding the PCM1792: Whether I got the current directions right or wrong is something that I was unable to be conclusive about from the datasheet. In my book, a source is a generator or driver if you wish, and a sink is a receiver. Thus I am in disagreement with you. I might very well be wrong though
Petter
Petter,
I think in fact we agree: "a source is a generator (-, current flows out of device) if you wish, and a sink is a receiver (+, current flows into device)", that's the same way SPICE works ...
;-)
About the pull-up/pull-down resistors we don't have to worry because they are much bigger than the input impedance of the I/V-converter which should be close to zero in best case.
AD in fact does recommend to use them in the AD1955 datasheet.
Best regards,
Norbert
I think in fact we agree: "a source is a generator (-, current flows out of device) if you wish, and a sink is a receiver (+, current flows into device)", that's the same way SPICE works ...
;-)
About the pull-up/pull-down resistors we don't have to worry because they are much bigger than the input impedance of the I/V-converter which should be close to zero in best case.
AD in fact does recommend to use them in the AD1955 datasheet.
Best regards,
Norbert
Norbert,
I bow my head and agree that the PCM1792 has quiescent current coming out of all analog pins
It does make sense that if the voltage at the output of the 1792 is near minimum supply voltage that current has to come out of that point. It is not as if the analog ground by itself can perform magic pull ...
Analog devices can go both ways if they place the output in between rails
Petter
I bow my head and agree that the PCM1792 has quiescent current coming out of all analog pins
It does make sense that if the voltage at the output of the 1792 is near minimum supply voltage that current has to come out of that point. It is not as if the analog ground by itself can perform magic pull ...
Analog devices can go both ways if they place the output in between rails
Petter
Have anyone tried the Volume control on These DACs??
Have anyone of you Tried to do a volume control changing the reference current is such DACs, AD1853, AD1955, PCM1730, PCM1738, PCM1792?? Analog devices Says something about this in their 1853 or 1955 datasheet.... But how does it sound and measure?? I'm going to try it sometimes, but not so soon...
Regards
Have anyone of you Tried to do a volume control changing the reference current is such DACs, AD1853, AD1955, PCM1730, PCM1738, PCM1792?? Analog devices Says something about this in their 1853 or 1955 datasheet.... But how does it sound and measure?? I'm going to try it sometimes, but not so soon...
Regards
I considered doing this for the 1853, but was adviced against it (or adviced myself against it) after hearing what Analog Devices had to say about the performance.
DAC design is very complex, and the units are actually optimized against a particular current. I suggested using a more accurate current source as well, but again in discussions received signals that this would probably "not help much".
In terms of audiohile experience, I would thus advice against it. Now, some of these DAC chips have built in volume control but they require programming through the SPI port which is a bit cumbersome for us mere mortals without a framework to build on.
Petter
DAC design is very complex, and the units are actually optimized against a particular current. I suggested using a more accurate current source as well, but again in discussions received signals that this would probably "not help much".
In terms of audiohile experience, I would thus advice against it. Now, some of these DAC chips have built in volume control but they require programming through the SPI port which is a bit cumbersome for us mere mortals without a framework to build on.
Petter
The Volume Ctrl
thanks, Peter, this seems to sound logical; I am on a close oppinion about this.
Mostly, these are audiophile parts and degrading the quality is prohibited
The internal chain of switches is more likely to prefer a constant rather than a variable current sourse. But I have heard bad things about the digital Control also, otherwise it is possible to be achieved. Also, I do not prefer the analog volume because of it's high noise and hum /over -105..-110dB/ which is worse than these DACs' SNR, and because of the high price of the better "Relay Volume" Conception also they are too big to be easily attachable ...
Regards
thanks, Peter, this seems to sound logical; I am on a close oppinion about this.
Mostly, these are audiophile parts and degrading the quality is prohibited
The internal chain of switches is more likely to prefer a constant rather than a variable current sourse. But I have heard bad things about the digital Control also, otherwise it is possible to be achieved. Also, I do not prefer the analog volume because of it's high noise and hum /over -105..-110dB/ which is worse than these DACs' SNR, and because of the high price of the better "Relay Volume" Conception also they are too big to be easily attachable ...Regards
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.