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Old 7th May 2006, 01:28 PM   #1
cviller is offline cviller  Denmark
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Question Comments on my cs8416 pcm1730 dac project

Hi

I would like to get some comments on my schematics. I have tried to follow the directions in the datasheets, but it would be great to if someone spotted potential mistakes before I start making the pcb. The cs8416 is configured in hardware mode and using I2S encoding for transfer to the pcm1730. I have tried it before, but I used too thin traces, so I guess the board had lots of opens and did not work. I think I'll use smd for the 47k resistors this time, because there are so many!

Should I consider adding a src4192 between the two to get better jitter performance?

How does 1730 sound compared to pcm1792/3?).

Is my power on reset too simple?

I have used the recommended decoupling - is that enough?
What are the most critical power nodes? I guess it would be VA on cs8416 and the 5V on the output of pcm1730.

If I decided to add a usb interface too, how could I mux in the signal?

I think I'll use Lars Nielsen's design for current-voltage conversion:
http://www.diyhifi.dk/DA_A1.pdf
When this works, the next step in my project is to make the line stage using tubes.


Thanks,

Christian
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Old 7th May 2006, 03:43 PM   #2
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Hey, I'm also working on a design using CS8416, which is a work in progress. I have a few questions. Why do you use the 47K resistors on pins 10-13? I didn't see that in the data sheet. Also, why do you pull pin 15 to gnd? Isn't it better to have the emphasis match on? Finally, I've been told to put 100 ohm resistors on pins 26-28, and don't you need a 47K pulldown resistor on SDOUT to put the receiver in HW mode (p. 44 data sheet)? Of course, I'm learning as well, so I beg you not to take my word as law. I just wanted to point these things out, so maybe someone can tell us who is correct. Good luck!
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Old 7th May 2006, 11:14 PM   #3
cviller is offline cviller  Denmark
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Thanks for your comments.
I was not sure about the 100 resistors, I guess it depends on what the load is. I know I need to connect sdout->47k->ground, but I guess I was too tired last night.
I don't understand your point with pin 15, because you connect it just like I do. You might be talking about pin 16, in that case I'll have to dig into the datasheet again.
Maybe I have misread the information in section 13.2 regarding pull up/down resistors, to me it just sounded like it needed to be done for all selections. But I guess you are right because pin 10-13 are not "start-up" option pins.

I have attached a version with a corrected sdout.
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Old 8th May 2006, 11:42 AM   #4
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You're right, I meant pin 16 (96 kHz). Now, I'm thinking you must be right about it though, because it is an output (after reset).
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Old 10th May 2006, 10:27 AM   #5
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I actually don't really know what the de-emphasis filter does and if it should be on or off. It sounds to me like it doesn't really matter because it is has something to do with selecting datatype and I'll only use it for audio.

I think you are right about the rxsel and txsel, so I have removed the resistors. I read that TX(pin 20) has it's own internal resistor, so should it just be connected directly to ground without a 47k resistor?

Any ideas on how to mux in another i2s signal? I guess it's a bad idea to use a hardware switch.

I was thinking about making the IV circuit on another pcb, is that possible, or are the current signals from the dac too sensitive to travel a few centimeters to another board? That way I can test different IV's later.
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Old 12th May 2006, 07:08 PM   #6
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I think you can make a separate PCB for the I/V. Look, for example, at the RAKK DAC, which uses that approach. I'm thinking about going with a balanced I/V on the same board using either AD8065 or AD8610 (which are pin compatible). It's hard to decide which op amp, because there are so many, but I think if the design is simple enough, I will be able to try several different ones, as long as they are pin compatible. I don't want to have to make different boards.
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Old 23rd May 2006, 04:13 PM   #7
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Promiteus makes a nice board w/power supply for the I/V output stage based on the Pass Labs DI. I bought a set without a dac design fleshed out with the intention of using a dac chip with differential outputs to drive balanced interconnects. I am new to this digital stuff and have yet to put together a pcb but was thinking of the same chipset with an iso150 digital coupler between chips for isolation. It seems like a easy addition but have not heard of any disadvantages. I will also post a couple of links to messages about input transformers for the digital input. Again, this seems like an easy addition and people seem to think that it helps clean up the signal. I am not in a position to start any new projects right now but have been reading everything on dacs that i can get my hands on and would be interested in following this conversation.
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Old 24th May 2006, 12:44 AM   #8
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I think I'll try the Pass Labs DI I/V stage as well. I have read some very positive reviews, but I still haven't found the schematics. My focus is finishing the digital part, but when that is done, I'm free to experiment with discrete I/V's based on bjt, jfet, mos and tubes. I have a schematics for balanced I/V using opamps, which I will also put in the comparison.

What are you gaining by inserting a digital coupler between the chips (I assume you are talking about receiver->dac)?

IMHO it will make more sense to do re-clocking, if you want to improve jitter performance. I have been playing with the idea of a src4192 between the devices, but it adds a lot of complexity and I would rather get a working board now than the perfect one.

Are you planning to etch your own pcb?
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Old 24th May 2006, 01:08 AM   #9
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I've attached an updated version of my design, which uses AD1896 for reclocking. That seems to be the most popular ASRC, as far as I can tell. From the data sheet, it really isn't that difficult to design a schematic. I'm going to try to prototype this thing within the next couple of months, if time permits. I'll keep you posted on my progress.
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Old 24th May 2006, 01:42 AM   #10
cviller is offline cviller  Denmark
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Looks quite simple.... maybe I should reconsider.
I thought you needed a clock source (oscillator) for reclocking - is that what you have connected to MCK on ad and pcm? What device do you use to make the clock and at what frequency?
Are you oversampling in ad1896? If you hardwire that stuff don't you have a problem when playing dvds (44.1 vs 46)?

EDIT: Oh, I didn't look at the last page. Is U7 a stock component? Is it really necessary with the tps3809? But, I think I'll see if my supplier something similar, because it might be more reliable than something I do with caps and resistors...
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