Is this quite a simple thing to do?
Do you just wire up two DAC chips in the same way and then connect the outputs together and reduce the gain in the I/V stage to account for the larger output current?
If this is the case then could I just place another DAC chip on top of the first one? With the SSOP adaptors ive got I think you can just piggy back them on top of each other, so it would be quite simple to add on another chip.
Cheers for any input Matt
Do you just wire up two DAC chips in the same way and then connect the outputs together and reduce the gain in the I/V stage to account for the larger output current?
If this is the case then could I just place another DAC chip on top of the first one? With the SSOP adaptors ive got I think you can just piggy back them on top of each other, so it would be quite simple to add on another chip.
Cheers for any input Matt
I cant see how this is worth doing. Linearly can be affected when the lower order bit from different DAC turn on when at different times. This also can affect the input impedances of the part. One part could current hog on another. Voltage references in the DAC can be affected implementation and degraded. You can end up with more noise and less dynamic range.
Konnichiwa,
Well, it seems the Engineers at BB/TI do not share your sentiments. Here some notes from their "Theory of operation" section:
"Superior performance and sound quality are produced by
combining the parallel connection of 4 DACs per channel.
This parallel connection technique produces very low THD+N
performance (up to –100dB) and wide dynamic range (up
to 112dB)."
EVM-1702 PCM-1072 EVALUATION MODULE Manual
With all due respect, you seem to have a very limited understanding of converters and how they work, and what important in their design and implementation.
Sayonara
jewilson said:
Well, it seems the Engineers at BB/TI do not share your sentiments. Here some notes from their "Theory of operation" section:
"Superior performance and sound quality are produced by
combining the parallel connection of 4 DACs per channel.
This parallel connection technique produces very low THD+N
performance (up to –100dB) and wide dynamic range (up
to 112dB)."
EVM-1702 PCM-1072 EVALUATION MODULE Manual
With all due respect, you seem to have a very limited understanding of converters and how they work, and what important in their design and implementation.
Sayonara
Sorry, that's not me. I forgot to place the link.
http://www.dddac.de/ma_dac21.htm
I found this projet very fine. Like an old tube amp... What will apen, if we use 256 chips!!!
http://www.dddac.de/ma_dac21.htm
I found this projet very fine. Like an old tube amp... What will apen, if we use 256 chips!!!
Parallel dacs.
Have a look at Accuphase www.accuphase.com They seem to think it is worth the effort.
Have a look at Accuphase www.accuphase.com They seem to think it is worth the effort.
I just looked at the accuphase web site - in one of their CDplayers (didnt look at more pdf files are rather large and even on DSL i cant be bothered ) they use 12 DAC chips
, six per channel, obviously they use a balanced output but six per channel seems a bit OTT. I would have thought 4 per channel would be a sensible place to stop.
) they use 12 DAC chips , six per channel, obviously they use a balanced output but six per channel seems a bit OTT. I would have thought 4 per channel would be a sensible place to stop.
Konnichiwa,
I am not sure what you are refering to. When Mr. Wilson used the exact same phrase applied to me in another thread you did not feel any need to moderate. Surely what is allowed one way cannot be wrong the other?
Sayonara
pinkmouse said:
Jim, Thorsten, knock off the personal stuff now please.
I am not sure what you are refering to. When Mr. Wilson used the exact same phrase applied to me in another thread you did not feel any need to moderate. Surely what is allowed one way cannot be wrong the other?
Sayonara
Konnichiwa,
I have thought about this too. What you get is an improvement in dynamic range of 3db per doubeling the number of DAC chip's in parallel. BTW, Voltage output DAC's can also operate parallel but they cannot be "stacked" the way it is possible with current output DAC's.
So, if lets start with a single PCM 1704 which is a notional 24 Bit DAC but has only -110db Noisefloor yet all the neccesary parts to have the LSB at (theoretically) -144db. So the DAC's possible performance at low level drowns in noise. Using 4 DAC's per channel will give us -116db Noisefloor, still 4db worse than 20 Bit equivalent performance. So, if we use 8 DAC's per channel we now have -119db for the noisefloor, nearly 20 Bit equivalent performance.
If we do further to 16 or even 32 DAC's per channel we could extend possible performance past -120db THD & N and thus would reap the full dynamic range from high resolution Digital Recordings. The fact that such recordings are few and far inbetween makes this of course largely academic.
And of course in the context of CD Standard audio with a limit of -93db on the recording (due to the 1/2 lsb uncertainty) all this is past academic. Hence one needs to understand what one wants to achieve.
A reason why one may parallel multibit converters for CD Audio is the use oif inexpensive DAC's with poor low level linearity, such as TDA1543. If you use one you have according to the datasheet -83db THD & N (@ -60dbfs) guaranteed and -90db as "typhical" performance. If we take -83db then using 8 DAC's in parallel will get us to -92db THD & N inherently and -99db for the "typhical" case, which would suggest that the recording becomes the limiting factor.
One might argue that using the TDA1543 in a DAC is retrograde and daft, however, if correctly applied the TDA1543 can produce a full scale output similar to any other CD player with only a Resistor as I/V Converter and at reasonable linearity. So there is good sense for using this obsolete DAC Chip with multiples in parallel.
Another reason to use multiple DAC's with CD is that many older DAC's as well as "economy" type DAC's tend to have a large variation of the exact (absolute) level produced at the lower and upper Bit's. This adds ceratain added non-linearity. As making DAC Chip's is a process that is goverend by the classic gaussian "bell" curve using one DAC chip will result in a performance that is all over the place, using multiple chip's in parallel will in effect place the result pretty reliably in the vicinity of the "peak" of that bell curve, making performance more consistent at very low and very high levels.
Now how any of the above sounds is a debatable issue. Whenever DAC Chip's are paralleled (and no matter how this is done either) I percieve some losses, especially in the are Id calle "immedicay". This is the key quality displayed by SE (and good PP) Valve Amplifiers and full range driver speaker display a great ofr and which is invariably lacking in systems using Multiway Speakers.
On the plus side, using multiple DAC's can sound smoother, more relaxed and refined. I found parallels here to using multiple other devices (Valves, Transistors, Op-Amp's) in parallel, in subjective terms you gain in some areas and loose in others.
Personally I'd say that the use of paralleled DAC's or not is governed by a number of parameters and depends entierly on the goals desired. To simply dismiss the use of multiple DAC's in parallel as stupid illustrates a deplorble lack of understanding of rather basic principle in Digital Audio, equally the blanket recommendation of paralleling up DAC's as cure for all digital evils shows a lack of understanding.
Sayonara
5th element said:
I have thought about this too. What you get is an improvement in dynamic range of 3db per doubeling the number of DAC chip's in parallel. BTW, Voltage output DAC's can also operate parallel but they cannot be "stacked" the way it is possible with current output DAC's.
So, if lets start with a single PCM 1704 which is a notional 24 Bit DAC but has only -110db Noisefloor yet all the neccesary parts to have the LSB at (theoretically) -144db. So the DAC's possible performance at low level drowns in noise. Using 4 DAC's per channel will give us -116db Noisefloor, still 4db worse than 20 Bit equivalent performance. So, if we use 8 DAC's per channel we now have -119db for the noisefloor, nearly 20 Bit equivalent performance.
If we do further to 16 or even 32 DAC's per channel we could extend possible performance past -120db THD & N and thus would reap the full dynamic range from high resolution Digital Recordings. The fact that such recordings are few and far inbetween makes this of course largely academic.
And of course in the context of CD Standard audio with a limit of -93db on the recording (due to the 1/2 lsb uncertainty) all this is past academic. Hence one needs to understand what one wants to achieve.
A reason why one may parallel multibit converters for CD Audio is the use oif inexpensive DAC's with poor low level linearity, such as TDA1543. If you use one you have according to the datasheet -83db THD & N (@ -60dbfs) guaranteed and -90db as "typhical" performance. If we take -83db then using 8 DAC's in parallel will get us to -92db THD & N inherently and -99db for the "typhical" case, which would suggest that the recording becomes the limiting factor.
One might argue that using the TDA1543 in a DAC is retrograde and daft, however, if correctly applied the TDA1543 can produce a full scale output similar to any other CD player with only a Resistor as I/V Converter and at reasonable linearity. So there is good sense for using this obsolete DAC Chip with multiples in parallel.
Another reason to use multiple DAC's with CD is that many older DAC's as well as "economy" type DAC's tend to have a large variation of the exact (absolute) level produced at the lower and upper Bit's. This adds ceratain added non-linearity. As making DAC Chip's is a process that is goverend by the classic gaussian "bell" curve using one DAC chip will result in a performance that is all over the place, using multiple chip's in parallel will in effect place the result pretty reliably in the vicinity of the "peak" of that bell curve, making performance more consistent at very low and very high levels.
Now how any of the above sounds is a debatable issue. Whenever DAC Chip's are paralleled (and no matter how this is done either) I percieve some losses, especially in the are Id calle "immedicay". This is the key quality displayed by SE (and good PP) Valve Amplifiers and full range driver speaker display a great ofr and which is invariably lacking in systems using Multiway Speakers.
On the plus side, using multiple DAC's can sound smoother, more relaxed and refined. I found parallels here to using multiple other devices (Valves, Transistors, Op-Amp's) in parallel, in subjective terms you gain in some areas and loose in others.
Personally I'd say that the use of paralleled DAC's or not is governed by a number of parameters and depends entierly on the goals desired. To simply dismiss the use of multiple DAC's in parallel as stupid illustrates a deplorble lack of understanding of rather basic principle in Digital Audio, equally the blanket recommendation of paralleling up DAC's as cure for all digital evils shows a lack of understanding.
Sayonara
Hello to all:
Is some ways, paralleling DAC chips could be compared to
the technique of "stacking" digital camera images to produce
a better image.
If you were to take 8 consecuitve frames of a still life image
with, say, a 2 mega pixal camera on a tripod, the 8 frames
could be aligned, summed and averaged using a suitable
program like "Registax" (free on the web). I have tried this
and note the following improvements:
1. Less noise in picture
2. Better dynamic range (light to dark)
3. Better details in dark or shadow areas
4. Better clarity
5. Improved color accuracy
Its like trading up to a digital camera with an improved
sensor chip. The improvement is not linear, so going with
an extremely large number of images (in most cases) does
not greatly improve on the technique.
Aside from the improvements of paralleling DAC chips (and
note that some of the Burr Brown chips already have 2
paralleled internal DAC circuits!), it is interesting to note
that at least Burr Brown grades some of their DAC chips.
The highest grade chips have the best S/N, lowest distortion,
and better linearity. And the sound that the highest grade
chips produce can be better than the average versions. I
once talked to an engineer at Wada, and he said that they
were using 4 BB1704 DAC chips in parallel (select grade)
at that time. And he said that it was well worth seeking
out the highest grade chips.
Fastcat
Is some ways, paralleling DAC chips could be compared to
the technique of "stacking" digital camera images to produce
a better image.
If you were to take 8 consecuitve frames of a still life image
with, say, a 2 mega pixal camera on a tripod, the 8 frames
could be aligned, summed and averaged using a suitable
program like "Registax" (free on the web). I have tried this
and note the following improvements:
1. Less noise in picture
2. Better dynamic range (light to dark)
3. Better details in dark or shadow areas
4. Better clarity
5. Improved color accuracy
Its like trading up to a digital camera with an improved
sensor chip. The improvement is not linear, so going with
an extremely large number of images (in most cases) does
not greatly improve on the technique.
Aside from the improvements of paralleling DAC chips (and
note that some of the Burr Brown chips already have 2
paralleled internal DAC circuits!), it is interesting to note
that at least Burr Brown grades some of their DAC chips.
The highest grade chips have the best S/N, lowest distortion,
and better linearity. And the sound that the highest grade
chips produce can be better than the average versions. I
once talked to an engineer at Wada, and he said that they
were using 4 BB1704 DAC chips in parallel (select grade)
at that time. And he said that it was well worth seeking
out the highest grade chips.
Fastcat
fastcat95
Increasing the dynamic of multiple stacked images for audio or video signals.
You can add multiple converted images together, the process is called stacking. Stacking can improve the Dynamic range and S/N of a signal however it is different than paralleling Dac’s on top of each other.
The process of stacking requires a filter algorithm that can process arrays of data. These arrays of data images or then stacked one on top of another what happen then is an a processor subtracts the noise that is random in the signal. The signal should repeat but the noise can jump around
so the algorithm remove the noise that does not totalize to the highest value.
Example: using an 8 bit word to simulate the signal you can see how this process works.
10101001
10101101
10101011
10101000
------------
10101001 signal
One of the issue with paralleling DAC’s is the decision points where the lower order bits turns is not always the same. When this happens, and it will in lower cost DAC’s it is possible for several types of errors to happen, depending on the DAC type being used. We can have offset bit error, a gain error, a differential nonlinearity error, and possibly create a non-monotonicity error in the bit we are converting.
Depending again on the DAC topology that being used it is possible to increase the current noise in the output. If we take two transistors and parallel them we get an increase in both current and current noise. If the noise is filtered out by the aliasing filter and there are no bit linearity issues it is possible to improve performance. However, I don’t believe you can keep getting a 3dB improvement while you adding noise currents in the output.
Thorsen, I looked over the BB EVM-1702 and the measurements described don’t match the methods used in the data sheets for the PCM 1702. In fact
the specifications for the data sheet or better in many cases. Maybe you know is the EIAJ filter the same as the A weighted filter?
fastcat95,
You mentioned, Wadia used the best grade parts for this application. However, to assure your getting the best performance from the DAC they should be graded for bit linearity to realize a performance improvement.
Another improvement is possible if we have missing codes in one dac and none in the other. We will find that most of the converters never meet their maximum linearity spec’s, it difficult to get true 18-20bit but after that all bet’s or off. What to look for in a dac is guarantee bit performance. I just have not seen consumer grade parts guarantee bit performance. Of course we still have not mentioned the noise and performance needed in a power to get to this level as well as the grounding. I Do like the ISO isolators used in the BB EVM-1702 that should help reduce the digital noise.
Increasing the dynamic of multiple stacked images for audio or video signals.
You can add multiple converted images together, the process is called stacking. Stacking can improve the Dynamic range and S/N of a signal however it is different than paralleling Dac’s on top of each other.
The process of stacking requires a filter algorithm that can process arrays of data. These arrays of data images or then stacked one on top of another what happen then is an a processor subtracts the noise that is random in the signal. The signal should repeat but the noise can jump around
so the algorithm remove the noise that does not totalize to the highest value.
Example: using an 8 bit word to simulate the signal you can see how this process works.
10101001
10101101
10101011
10101000
------------
10101001 signal
One of the issue with paralleling DAC’s is the decision points where the lower order bits turns is not always the same. When this happens, and it will in lower cost DAC’s it is possible for several types of errors to happen, depending on the DAC type being used. We can have offset bit error, a gain error, a differential nonlinearity error, and possibly create a non-monotonicity error in the bit we are converting.
Depending again on the DAC topology that being used it is possible to increase the current noise in the output. If we take two transistors and parallel them we get an increase in both current and current noise. If the noise is filtered out by the aliasing filter and there are no bit linearity issues it is possible to improve performance. However, I don’t believe you can keep getting a 3dB improvement while you adding noise currents in the output.
Thorsen, I looked over the BB EVM-1702 and the measurements described don’t match the methods used in the data sheets for the PCM 1702. In fact
the specifications for the data sheet or better in many cases. Maybe you know is the EIAJ filter the same as the A weighted filter?
fastcat95,
You mentioned, Wadia used the best grade parts for this application. However, to assure your getting the best performance from the DAC they should be graded for bit linearity to realize a performance improvement.
Another improvement is possible if we have missing codes in one dac and none in the other. We will find that most of the converters never meet their maximum linearity spec’s, it difficult to get true 18-20bit but after that all bet’s or off. What to look for in a dac is guarantee bit performance. I just have not seen consumer grade parts guarantee bit performance. Of course we still have not mentioned the noise and performance needed in a power to get to this level as well as the grounding. I Do like the ISO isolators used in the BB EVM-1702 that should help reduce the digital noise.
Konnichiwa,
I know few DAC's where this could be expected. All multibit DAC's known to me are SUPPOSED to update the current output on the change of WS/LE. Now if they do not settle their current very quickly they would not be able to provide any kind of performance. I will agree that there may a minimal difference in the slope time between chip's, but with the same FAB and methodes this again should be minimal and small enough to avoid any notable glitches.
I would severely question that. Most DAC's settle their output current extremely quickly, the amount of time spend setteling compared to the amount of time at "steady state" MUST be MINIMAL and resonably CONSISTENT sample to sampel for the darn thing to work at all....
Virtually anything is possible in this universe, but most things are HIGHLY unlikely.
Yes, the absolute current and the absolute noise current both rise. BUT the relative noisecurrent (compared to tho the operating current) goes DOWN.
Based on a variety of published measurements - you can.
The EIAJ specification of dynamic range etc. is more stringent (IIRC) but also remember that the EVM is charaterised as complete system, the 1702 per datasheet as "chip only".
Ciao T
jewilson said:
I know few DAC's where this could be expected. All multibit DAC's known to me are SUPPOSED to update the current output on the change of WS/LE. Now if they do not settle their current very quickly they would not be able to provide any kind of performance. I will agree that there may a minimal difference in the slope time between chip's, but with the same FAB and methodes this again should be minimal and small enough to avoid any notable glitches.
jewilson said:
I would severely question that. Most DAC's settle their output current extremely quickly, the amount of time spend setteling compared to the amount of time at "steady state" MUST be MINIMAL and resonably CONSISTENT sample to sampel for the darn thing to work at all....
jewilson said:
Virtually anything is possible in this universe, but most things are HIGHLY unlikely.
jewilson said:
Yes, the absolute current and the absolute noise current both rise. BUT the relative noisecurrent (compared to tho the operating current) goes DOWN.
jewilson said:
Based on a variety of published measurements - you can.
jewilson said:
The EIAJ specification of dynamic range etc. is more stringent (IIRC) but also remember that the EVM is charaterised as complete system, the 1702 per datasheet as "chip only".
Ciao T
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.