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Old 29th June 2004, 10:17 PM   #1
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Default My first DAC hurrah.

Yay! Ive been wanting to make one for ages and have now finally completed the thing!

Basically lots of thanks go the MWP for the use of his DAC schematic as guidance, I had no idea whatsoever what was required to build a DAC before this. Anyway.

My version uses the DIR1703 SPDIF receiver coupled with a PCM1798 DAC chip. OPA627 perform the first pair of opamps after the DAC and then Analog devices AD797's for final shunt.

The IV stage has metal film 1% resis and high quality polystyrene caps.

The pin configuration for the 1798 is identical to the 94, if I can get hold of one from somewhere Ill see how much the better the superior chip sounds over the 98. I cant get samples of the 94, nor can I find anywhere to buy them from? As this is meant to be TI's flagship along with the PCM1792 you'd think they'd want then to be available to people.

Anyway now on to the good stuff, sorry no pics for the moment as the camera is not working currently with my PC (USB troubles), but appart from that it sounds great! no doubt this has something to do with my other post about grounding and all the negative comments I got from my old PCB made me redo it, much better. In comparison to my TEAC T1 dac it is better, which was the object of this exercise.

The bass is noticeably more tuneful and tighter, its very smooth sounding without any spit or harshness to it. The T1 was also very smooth too but not quite as smooth as this. The noise floor is obviously lower aswell and upon trasients or climax the sound does not seem to compress as much (compress is the wrong word). Absolute detail in single instuments or voices on their own is not that much different to the T1. The big difference is in micro detail, small sounds in the background are more easily apparent and some sounds that id not heard before are now present. All in all im very pleased with the results and am hoping it will only get better the more its used. The one thing im impressed with is how quiet it is, SILENT! wonderful.

One bit of experience (appart from learning how to make a DAC) ill take away from this is the use or SSOP to DIP converters, or just soldering SSOP in general. MAKE SURE THE PINS ARE SOLDERED DOWN!. I've had much heartache over it not working well because a couple of pins were not making contact properly.
I followed someone elses guide to soldering them which invoves soldermop or wick, this works really well, no more fretting over two pins soldered together.

Oh and those who say the DIR1703 data sheet is confusing, its not that bad you just need to get your head around it. OK I cant read those digital graphs but you dont really need to, to be able to make something of the chip.

Cheers Mat
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Old 29th June 2004, 10:44 PM   #2
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Nice!

Make sure to post pics asap
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Old 2nd July 2004, 09:05 PM   #3
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OK update, still no pics... they will come when I open up the DAC unit again when I get another PCM2902 shortly arriving, I fried the first one lol.

Anyway sound update. Having let this thing run in a little and let me acclimatise to it I now realise how much better it is then the T1 DAC. Everything is just better, no more needed, the trebble is better, the midrange is better and the bass is better. Nuff said unless you have a top DAC Id strongly advise building one around the PCM179x series of chips. Ive found a source for the PCM1794 so will order one and see if its any better then the 98.

If you like a very detailed smooth and brilliantly seperated sound youll love the PCM1798.
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Old 2nd July 2004, 10:22 PM   #4
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I'm happy for you, when somthing you make by your own is sounding better then the things you buy your happy right?
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Old 3rd July 2004, 02:36 AM   #5
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Quote:
Originally posted by tobias_svensk
I'm happy for you, when somthing you make by your own is sounding better then the things you buy your happy right?
Most definately happy


My speakers sound better then ones you buy, my amps sound better then the ones I had bought and now the DAC completes the chain. All my hifi is me made! appart from the digi source which is a computer, which I think ill leave to the pros lol.
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Old 3rd July 2004, 06:41 AM   #6
MWP is offline MWP  Australia
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Well done.
Get those photos up ASAP

What other DACs are you comparing it against?
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Old 3rd July 2004, 08:59 AM   #7
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Hallo,

Is that DAC digitally filtered or NONOS?
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Old 3rd July 2004, 10:48 AM   #8
Nisbeth is offline Nisbeth  Denmark
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Hi Mat

Congratulations on your project. Will you be willing to share the schematic and board layout?


/U.
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Old 3rd July 2004, 12:13 PM   #9
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Im comparing it against a TEAC T-D1 dac which is the parter for the VRDS T1 transport. I have both but now use neither.

The DAC is digitally filtered atleast I think it is.

Ofcourse I will post schematics and board layouts if people want them. The schematic is basically MWP's DIR1703 inplementation with TI's implementation of the PCM1798. Im not entirely sure how to get the board layout in a format thats accessable to everyone. I designed this on electronics workbench ultiboard, any ideas any1?
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Old 3rd July 2004, 10:50 PM   #10
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OK I decided to whip the lid off and took a few pics in the process.

Right first pic the DAC clothed, I have not yet made a front panel so as you can just about see in the pic there are a few holes in the front. The case used to be a very high voltage PSU used for running gels which separate DNA. This was very handy as it had a filtered mains inlet with a switch and two fuses already mounted. I spray painted the lid black. The back panel hints to the origins of its original colour. Not very hifi!
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