PCM1794 State off art DAC?? - diyAudio
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Old 5th August 2005, 07:01 PM   #1
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Default PCM1794 State off art DAC??

Hello.

I have new searched this great and informative forum for Hours, but no luck off what I am searching

I am looking for a dac kit with PCM1794 and and good reciever like CS8416 and DF1704.

I have seen K and K audio new "Baby"
I think it´s close to my wish, but a bit to costly and limited DIY
I got an analog outputstage.

So please come with your suggestions and comments for a state off the art Dac kit with pcm 1794

Best regards
Kim
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Old 6th August 2005, 12:30 AM   #2
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There used to be an evaluation board which could house 1792, 1794 + the DSD variants. I just aquired one in the secondhand market a 1792 version which I have modified to 1794 (replacing the chip seems to be the only thing you need to do).

Anyway, the unit was made by BurrBrown (now TI) and appears very user friendly in that it has jumpers between input section and DAC. Cool for prototyping.

It also has the other parts you are searching for.

The situation is pretty much like this: Chip vendors make evaluation boards that more or less get copied wholesale. Manufacturers (in the audio space who typically have limited competency in digital work) do some minor tweaking of the input receiver + do their own power supplies and typically replace the output filter with their own design. The chip guys typically have their designs optimized for measured specifications (paper), so this works pretty well. The practical upshot of this is that except for digital filter redesign (which more have started getting into now) you can do a damn decent job of your own DAC design.

The problem is building it (soldering) and costs of tight boards with thin traces. You can get adapters to DIL though, but you still need to solder that one chip + your performance will likely hurt you (by how much I have no idea).

By the way, if you look at the specs of the PCM1794, it has a digital filter built-in which looks much like the DF1704 on paper (without knowing the interals, I expect they lifted their DF assets into the chip).

Petter
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Old 6th August 2005, 12:07 PM   #3
JohnW is offline JohnW  Hong Kong
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The DSD1792/4 has a Stopband rejection of greater then -130dB, where as the DF1704 "only" has a Stopband rejection of -115dB.

I've used the DSD1794 on a couple of Pro Audio projects, and had problems with THD. There’s seems to be an issue with production variance. Depending in Chip / IC batch some channels result in ~ THD+N of 0.00035%, while other channels result in ~ 0.0025% - mostly second harmonic. The "poor" performing channels have imbalances in DC on the output of the I/V converters - I guess indicating internal miss-match of I/V currents - which would explain the non cancellation of even-order components.

I contacted TI about the problem - and after about 1 month I got a reply asking me to send to there QC department 10 good devices, and 10 poor devices - the company for who I did the design for paid about US$27 for each device - this would mean sending TI US$540 of ICs to help them investigate there own QC issues!

The "poor" performing devices I’ve used have a batch code of 48M113M.

Also watch the performance graphs – results very much depend on which mode you operate the device - the Graphs always seem to be shown in "Best" operating mode.

Cheers,

John
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Old 6th August 2005, 12:31 PM   #4
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Hey

Thank you both for your input.

As I know off the PCM 1794 has built in "DF1704" so..

Do any off you worked with upsampling circuits from 16bit 44khz to 24bit-192kHz sampling before D/A converter?

Kim
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Old 8th August 2005, 10:42 PM   #5
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Quote:
Originally posted by JohnW


[snip]

Also watch the performance graphs – results very much depend on which mode you operate the device - the Graphs always seem to be shown in "Best" operating mode.

JohnW,

Thanks for conveying your concerns re performance of some of your chips. I have a very different datecode but will try to get one of them measured soon.

If you could shed more insight into '"Best" operating mode' I would greatly appreciate it.

Petter
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