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Old 27th April 2012, 06:50 PM   #11
ch33ta is offline ch33ta  Croatia
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Great - finally a separate thread for this DAC

And for my contribution;

High-res photos of the board:
FRONT
BACK
Those come in handy for the modifications...

And the SCHEMATIC which is a little old and it's missing D+3,3 PSU section, but the rest is ok...

Concerning higher sample rate playback (above 96kHz);
On the board above CS8416 pin 20 (TX) is set high, this enables faster Phase Detector Update Rate - you get less jitter, but it will play only up to 96kHz (108kHz according to Cirrus)...
More on the matter in the official "papers"; http://www.cirrus.com/en/pubs/appNote/AN339REV1.pdf
Some say it works with higher sample rate - possibly a different revision of the board?

All in all - a great little DAC for a few pennies
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Old 27th April 2012, 07:34 PM   #12
TheGimp is offline TheGimp  United States
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Default Schematic w/ 3.3V supply

Since there is no copyright on the schematic I'll upload it.
Oops, schematic too big. I'll downsize it and upload it.

My board has been hung up in USPS for the last four days. I was hoping to get it today but no joy.

Also in the event that someone finds this thread later on, there is another thread that has a lot of good points that should apply to this board as well ..

DAC 2496 (AK4393) DAC KIT With CS8416+AK4393+5532
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File Type: jpg LJMSchematic.JPG (112.6 KB, 826 views)

Last edited by TheGimp; 27th April 2012 at 07:54 PM.
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Old 27th April 2012, 10:16 PM   #13
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The analog stage in the schematic is not really as recomended by CL. It "works", but I have a feeling that it could do better.
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Old 28th April 2012, 01:07 AM   #14
TheGimp is offline TheGimp  United States
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It should be pretty easy to change it to the one in the data sheet. most of the component placements are the same, so it is mostly value changes. IIRC two caps and one resistor are different topologically.

I did a sim of both and they are quite different. On the other hand, I understand the values on the schematic may not be what is on the board. The same filter is shown on some other schematics (4793/6?) from what I understand, and they did not match the boards values.

ch33ta! you reversed the bottom layer so it is like an x-ray view!

I've been driving myself nuts for 10 minutes tracing out the power supplies.

Last edited by TheGimp; 28th April 2012 at 01:26 AM.
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Old 28th April 2012, 02:21 AM   #15
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The AMS1117 datasheet recomends as minimum output capacitor a 22uF tantalum.
I guess bypassing the electrolytic with 100nF is a good alternative, but I will increase the capacitor to more than 10uF. Datasheet says that bigger capacitors are not a problem due to internal reverse diodes, so I am looking to something in the 47-220uF range.
The 7812 and 7912 that take care of the OpAmp power could see some improvement too...
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Old 28th April 2012, 03:49 AM   #16
TheGimp is offline TheGimp  United States
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I'd skip the Tantalum and go with some good low ESR Al caps bypassed with film caps at 1/100 the value of the Al cap. I think I would have been better off with a kit in that regard so I wouldn't have to remove the caps and re-solder new ones. But I got the built one at the cost of the kit....

I'm not quite sure what to do with the 78/7912s. LM317s are better, but if you are going to change the topology it might be worth it to go shunt reg.

A small pc board with a shunt regulator that pin-d the same as the 7812/7912 would be neat.

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Old 28th April 2012, 06:06 AM   #17
ch33ta is offline ch33ta  Croatia
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Quote:
Originally Posted by TheGimp View Post
...
ch33ta! you reversed the bottom layer so it is like an x-ray view!
I've been driving myself nuts for 10 minutes tracing out the power supplies.
Yes, sorry, forgot to mention that
Bottom side is mirrored, it's much easier for me to trace the lines that way...

BTW. most of the datasheets for LDO regs doesn't recommend using low ESR caps (like Oscons)... In LM1117 datasheet they say that the output cap ESR should be 0.3Ω - 22Ω - so I pretty much stick to that recommendation and avoid Oscons with lower ESR after the reg...
100uF tantalum & 100nF film cap should do great...
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Old 28th April 2012, 04:08 PM   #18
TheGimp is offline TheGimp  United States
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X-ray is better for me as well. It is what I'm used to for Check-Plots of PWBs. It just threw me because it was a picture, not plots.

I just don't like Tantalum. I diagnosed a problem with them back around 1983 when I worked for TI on the 520/530 product line. The Tant caps were used for decoupling on 12 bit D/A converters. They were being degraded by either ESD during manufacturing of the boards, or transient surges after assembled. The tant caps would fail later on. Analysis with decapped parts that were imaged with a SEM allowed us to finally figure out what was happening.

Today's tant caps are better, but not good enough. Our design requirements where I work is to remove all tants from re-designs for reliability reasons, and not to use them in new designs.

For these reasons I recommend Al and film.

That said, my board arrived today. First off I measured the input caps at about 1.2Ohm ESR. I'll probably replace them with with some low ESR 4700uF caps I have, if I can find transformers that will result in input voltage not greater than 16V.

First though I'm going to run some frequency sweeps and distortion measurements to get a baseline for the changes, change the caps and run the tests again.

I'll probably run a burn-in on the board for 100hrs after that before I change anything else.
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Old 28th April 2012, 04:47 PM   #19
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I did use two Radioshack transformers (shielded). They have 2x6V and 2x12.6V AC.
I did buy a toroidal also (with all the necessary voltages), but at second thought I decided to try the regular ones first.
Frequency sweeps shouldn't show nothing special. The distortion ones are important - but they require a good ADC.
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Old 28th April 2012, 05:40 PM   #20
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Toroid transformer are worse for conducted noise from the line getting into your power supply. I suppose one could use a common mode filter on the power supply to help suppress it.

On the other hand, EI core transformers radiate more 60Hz noise. Pick your poison I guess. I probably have EI transformers that will work so I may buy a toroid for comparison later on.

I would expect the difference to show up when measuring the floor noise.
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