I am a NOOB and i want to do a 1794 DAC!! - diyAudio
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Old 7th December 2005, 04:35 AM   #1
JinMTVT is offline JinMTVT  Canada
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Join Date: Jul 2004
Location: MTL
Default I am a NOOB and i want to do a 1794 DAC!!

ok i know nothing about all that ..but i just wanna do some crazy 3d electronic scultptures, and i want it to actually do something!

So this is my next project!

With my almot NONE knowledge about electronics and DACs , i will be building a 1794 DAC for my headphone amplifier!

so i went to look out for info from TI.com

http://focus.ti.com/lit/ug/sleu037/sleu037.pdf

is this their evaluation board?

i guess that one could only use the needed parts from this and make a few simple changes ?

Is that a good design to start with ?
I want it to be as simple as possible!

so what do i need to do this ?

CS8414 ( that's the input chip ? )
PCM1794 ( a few of em, since i might just burn some )

is the output stage correct in this schematic ?

wtf are UA1-7 supposed to be ?
i guess that they arne't just sockets right ?
the triangle pointing right with +- are op amps right?
what to put there?

So you guys think that i can do it or not ?

should be a nice project for a noob as me
hehe

What do you recommend to do for output if i want to use this with Peranders QVR-02 or 07 headphone amplifier?

i'll start ordering chips as soon as someone can tell me what should i use for UA1-7

also why they do 2 output ? 4.5VRMS and 2VRMS?
what to use ?

thanks all
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Old 7th December 2005, 01:14 PM   #2
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Some of us here are fairly new too.

I will also be doing the same, although not from the evaluation board and I need to build in some design consideration to allow future expansion for external digital filters and a competely different output stage.

Where you ask questions about what things are; your assertions have been correct.

Whether you can pull it off depends on how much electronic theory, understanding of the associated calculations you can absorb in the time you have.

I would start with trying to understand basic electronic components and then start looking at how to construct basic power supplies. You will not need the top quality PSU designs from this website if you are doing a sculpture and just want something functional as opposed to out-and-out quality sonics.

From learning about PSUs, you will need to learn about DAC, binary notations, DAC clocks, jitter and associated factors with DACs such as out-of-band intermodulation distortion noise. After that, you need to learn how to remove such noise with appropriate designs in the output stage to remove it. This would involve learning op-amp theory. Again, you will not get a top quality design, but it's easy to better entry level separates hifi.

It is an awful lot to attempt as a newbie, especially if this is a college course related sculpture as you may not have enough time. However, it is possible.

I say you should try. You may find a whole new hobby/skill, since circuit design itself is a form of sculpture.

Good luck,

InfiniteGain
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Old 7th December 2005, 10:01 PM   #3
JinMTVT is offline JinMTVT  Canada
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hi infinitegain nice nick

i am not at school at all ..
and time is extremely limited for me
working 60 to 90 hours /week
( own buisness )
so i do not think that i will be able to learn much,
i will have to stick with already designed sections...

"... binary notations, DAC clocks, jitter and associated factors with DACs such as out-of-band intermodulation distortion noise"

i would certainly like to learn all that
but i am sure that i won't be able to get all that ..

heck i'll just fry a few chips , till i get something working at the end
shouldn't be that hard to copy parts of designs from fellow diy here, trying to understand a bit while doing it..

what to get for the output stage?
is the design on the ev board any good?
what voltage output to perhanders headphone amp?


i am not pointing to ULTIMATE sound quality, but i sure would like to have something better than my pc sound card, else it wouldn't have any point of building ..
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Old 7th December 2005, 10:11 PM   #4
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Location: Greenwich, London, UK
OKay.... you work too many hours. Think about your heart health.... it's no good working that many hours! You'll keel over too early to have enjoyed the fruits of your labour!

Okay... yes, I agree that is not enough free-time to do what I said. Best find somebody's transport design going to a digital output (coaxial). Then find somebody's simple external DAC design which uses a coaxial input. Marry the two circuits together in one board.. et voila!!

Not sure how it would sound, but it cannot be too bad.

Good luck!!

InfiniteGain
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Old 7th December 2005, 11:18 PM   #5
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Default Re: I am a NOOB and i want to do a 1794 DAC!!

Quote:
Originally posted by JinMTVT
I want it to be as simple as possible!
http://diyhifi.230v.dk/dac1.html

Replace the '1730 with the 1794.
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Old 8th December 2005, 04:11 AM   #6
JinMTVT is offline JinMTVT  Canada
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Join Date: Jul 2004
Location: MTL
i thank you very much for this link...

lets take a look to see if i get something out of this!
( i find cool right now that the more i look at schematics, the more i understand what does what ... i used to not even understand anything at all .. hehe )

First thing :
http://diyhifi.230v.dk/powervd.html
http://diyhifi.230v.dk/powerva.html

what is suppposed to be the difference between
digital powe supply and analogue one ?

i don't get it ..is it because we want it to be completly seperate structures ? interfence ?
i guess that digital side works at way higher speeds, so it would shoot back signal into the analogue stuff?

i have this book called" teach yourself electricity and electronics" by Stan Gibilisco

i read about half of it, all the boring part

so do have a basic understanding, but i odn't quite figure out the maths until i get it explained

I do know how PSU works, transfo -> rectifier - > filter -> regulator ... just don't need wich quality parts to get?

that will be a problem with me, i don't konw how to chose wich parts to get for quality ....are there none brands that we need to use on audio components?
are there parts wich we don't care much of the quality?


then about this schematic here :
Click the image to open in full size.
http://home.tiscali.dk/larsbnil/diagrammer/powerva.jpg

What is the difference in lets say C20 and C21 ?
are they both capacitors? why the difference in the representation ?

then i don't quite get what exactly are D12 D13 and D7
?? those are for the voltage drop ?

how to know wich side gots the correct polarity when designing all that ?

and then why is there no negative side on the digital voltage ?? not required ?

IS this design a good ? average? super PSU design?

i'll study all this for now, the more i look at it
the easier it gets to understand
( i guess that it is a good sign )
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Old 8th December 2005, 10:50 AM   #7
guzzler is offline guzzler  Scotland
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Personally, I wouldn't use this design, just go with the usual LM317/LM337 combination for analogue, and LM317 followed by low-noise LDO regulator on the digital side (I like the REG102s from TI). This would be a nice, clean power supply, very easy and tolerant.

C20 and C21 are both capacitors; the difference is convention. The curled one with a polarity indicated is an electrolytic, whereas the straight one is a film of some type (I would use polyester in a PSU, and ceramic for bypassing)

The diodes you mention are zener diodes, and set the output voltage of the supply, plus the voltage drop across the transistors (around .7V)

Digital only needs to swing between +Vcc and 0V, so no need for positive and negative halfs like the analogue ones. In most DAC designs you'll see some form of DC blocking after a voltage output, as the output from the DAC sits at usually 1/2 Vcc
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Old 8th December 2005, 10:58 AM   #8
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Join Date: Oct 2001
Location: .
Quote:
Originally posted by JinMTVT
i thank you very much for this link...

lets take a look to see if i get something out of this!
( i find cool right now that the more i look at schematics, the more i understand what does what ... i used to not even understand anything at all .. hehe )

First thing :
http://diyhifi.230v.dk/powervd.html
http://diyhifi.230v.dk/powerva.html

what is suppposed to be the difference between
digital powe supply and analogue one ?

The analogue and digital sections require different voltages.

Quote:

i don't get it ..is it because we want it to be completly seperate structures ? interfence ?
i guess that digital side works at way higher speeds, so it would shoot back signal into the analogue stuff?
Something along those lines, yes.

Quote:

i have this book called" teach yourself electricity and electronics" by Stan Gibilisco

i read about half of it, all the boring part

so do have a basic understanding, but i odn't quite figure out the maths until i get it explained

I do know how PSU works, transfo -> rectifier - > filter -> regulator ... just don't need wich quality parts to get?

that will be a problem with me, i don't konw how to chose wich parts to get for quality ....are there none brands that we need to use on audio components?
are there parts wich we don't care much of the quality?
If you go with the power supplies linked to above then your scope for rash overspending is limited. Anything you get from Digikey/Farnell/RS will probably do.

Quote:

then about this schematic here :
Click the image to open in full size.
http://home.tiscali.dk/larsbnil/diagrammer/powerva.jpg

This is a Capacitance multiplier with a diode added to provide some regulation.

Quote:

What is the difference in lets say C20 and C21 ?
are they both capacitors? why the difference in the representation ?
They are both capacitors with C20 being a film cap for high frequency bypass duties and C21 an electrolytic performing the bulk of the work of suppressing whatever ripple is left after the C-multiplier.

Quote:

then i don't quite get what exactly are D12 D13 and D7
?? those are for the voltage drop ?
The C multiplier is not a regulator. Adding the diodes provides some regulation. Which begs the question, is it still a C- multiplier? But I digress.

Quote:

how to know wich side gots the correct polarity when designing all that ?
The datasheets.

Quote:

and then why is there no negative side on the digital voltage ?? not required ?
Some dacs require a negative supply, the PCM1730 and PCM1794 do not.

Quote:

IS this design a good ? average? super PSU design?
It is as good a place to start as any. From here on things get more complicated and the potential pitfalls increase accordingly.
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Old 8th December 2005, 01:54 PM   #9
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As a "good place to start" is this design any better than the DAC I am likely to find in my run of the mill CDP or receiver? (thinking of 2 PCM1794s in mono mode to get balanced outs)

Would my money be better spent upgrading my CDP's clock?

Thanks
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Old 8th December 2005, 04:12 PM   #10
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Quote:
Originally posted by BobEllis
As a "good place to start" is this design any better than the DAC I am likely to find in my run of the mill CDP or receiver? (thinking of 2 PCM1794s in mono mode to get balanced outs)

Would my money be better spent upgrading my CDP's clock?

Thanks

With balanced '1794s I'd be minded to put a bit more effort into the power supplies and the output stage but the odds are it would be better than the run of the mill player/receiver as is.
You could upgrade the clock for as lot less than the cost of a twin PCM1794 dac. Adding a Tent canned oscillator is a fairly simple and inexpensive upgrade.
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