Micro DIR9001 + PCM1794A DAC - diyAudio
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Old 22nd November 2008, 03:51 AM   #1
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Default Micro DIR9001 + PCM1794A DAC

After not getting a response to a question I posted in this thread, I decided to see if there was any chance I could manage to get one put together myself.

Nearly 13 hours of reading, squinting, and building later I have myself the DAC I was after. Like always, my determination has overcome my ignorance and the little DAC worked the first time I powered it up. I really don't know how I do it.

The circuit is a culmination of the datasheets for the DIR9001/PCM1794A evaluation modules, the TwistedPear Audio COD, and any other info I could find.

I managed to get the thing made single sided with only one jumper (and a ground plane). There is no input buffer as I only plan to use Toslink receivers. The output is just passive I/V resistors, but I plan to build another board the same size with OPA1632/THS4131 that will sit piggyback. I have to manually reset the circuit right now, but I put a spot on the board for a TPS3809K33, I just don't have any on hand.

I'm listening to it right now using half of the balanced I/V output with a single ended amp. The gain is low, but it sounds good so far.

Here are some really bad cell phone pics (my camera is out of town for the weekend). The last pic is the micro DAC next to an Entech 203.2 PCB with a DIR9001 -> CS8412 converter board.

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Old 22nd November 2008, 04:50 AM   #2
xaudiox is offline xaudiox  Philippines
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Wow nice job.. cute dac too..
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Old 22nd November 2008, 07:08 AM   #3
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13 hours... congrats, awesome work.

I've got a DIR9001/PCM1796 (yeah, with a microcontroller) design on the back burner. One interesting thing about the DIR9001 is that the jitter of the recovered clock varies with the fs multiplier, according to a chart in the datasheet. I'm curious whether optimizing this makes an audible difference.
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Old 22nd November 2008, 07:26 AM   #4
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Quote:
Originally posted by mako1138
One interesting thing about the DIR9001 is that the jitter of the recovered clock varies with the fs multiplier, according to a chart in the datasheet. I'm curious whether optimizing this makes an audible difference.
Well, my little board doesn't have a single inductor or ferrite bead and the digital and analog grounds share the same ground plane; so I doubt it matters much for me at least.

I had to make some compromises with the design as I'm not patient enough to wait for parts to be ordered and I'm limited to 1"x5" PCB strips. I think it turned out good even with the shortcuts I took. I don't hear any strange hiss or hum coming from the speakers.

I need sleep now. I worked on this from the time I got home from a night shift at 8AM until around 9PM and I'm still up at 2:30AM . I think I will play some "TV on the Radio" through my new little DAC friend and pass out.
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Old 23rd November 2008, 02:04 AM   #5
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I threw together a p2p circuit with an INA2134 and put it on the output of the dac (with the passive I/V resistors still in place). The output signal is about 1.7VRMS now and it sounds amazing. I can't wait to try the THS4131.

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Old 23rd November 2008, 08:31 AM   #6
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Here is a schematic for anyone that might be interested.
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File Type: pdf microdac.pdf (31.9 KB, 1313 views)
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Old 23rd November 2008, 03:06 PM   #7
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There is a mistake in the above schematic, the 68nF and 4.7nF filter capacitors are switched.
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File Type: pdf microdac.pdf (39.0 KB, 1199 views)
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Old 2nd December 2008, 03:51 PM   #8
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Can anyone tell me if it would be worth the effort to shoehorn a SRC4192 into this circuit? I think the DAC sounds excellent as is; would it really make that big of a difference?
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Old 4th December 2008, 08:41 PM   #9
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Hi,

very nice work....I am Fan of tiny high end DIY work.

cheers

Alan
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Old 5th December 2008, 10:03 AM   #10
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Thank you, I like the challenge of making them small. I think I need to switch to 0603 parts, 0805 seems so big to me now after >3 years of soldering them.

When I finish the active I/V board it will stack on top of the DAC. I think I will put the +5v regulator on the I/V board so all I will need is a +/-15v supply.

So no one has an opinion on reclocking with with the SRC? I just want to know if it would be a night and day sort of thing, or if it is like comparing a polypropylene cap to "better" polypropylene cap.
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