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Old 11th March 2012, 05:48 AM   #411
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by s3tup View Post
This one goes to production tomorrow
Have fun.

However you realise that you have more suboptimal design features than I can cover in one post?

Have you actually read the the thread and those referenced within?

What you have will work about as well as what Philips and Marantz did in their 1980's CD-Players.

Ciao T
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Old 11th March 2012, 06:32 AM   #412
regal is offline regal  United States
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One post (well two) from Guido elsewhere:

Quote:
part 1 power supply

digital part: all logic is current mode (constant current).
most of the supply +5 to -5, lesser part +5 to dgnd.
Capacitive spike to -15V.

analog part: -15: current reference generator, dem oscillator and
ring-counter. Not to agnd, but to -5. :!:
This 10V should be as constant as possible.

Decouple all supply pins and DEM caps to agnd.

Logic before dac (e.g. for reclocking) and the caps to filter the i2s inputs (see i2s chapter) also to dgnd.

agnd - dgnd should then only be some dc current.

part2: i2s inputs

Reclocking needed on ALL inputs (to avoid disturbance due to jitter on the inputs). Output latch is clocked on BCK pulse in i2s mode (1541A).

input voltages low 1.3 min (1.2 for safety) and high 1.5V max (1.6 for safety). So instead of 'TTL levels' 1.2 and 1.6V.

Rise time not faster than 10nsec, reduce speed with 10pF cap to dgnd (RC filter: 1k resistor and 10pF cap). Drive this RC filter in such a way that 1.2 for low and 1.5 for high goes to the dac.
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Old 11th March 2012, 07:09 AM   #413
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Thorsten,
Do you refer to lack of:
- DEM clocking,
- I2S attenuation
- I2S reclocking
- Shunt regs
I'm well aware of these. I2S things will be on digital board, shunt regs is a matter of choice, and DEM clocking - i'll try without it.
Or there are more suboptimal design features?

Regal, these suggestions are from HtP, he is somehow related to Phillips:
TDA1541 info
Nice read...

Last edited by s3tup; 11th March 2012 at 07:23 AM.
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Old 11th March 2012, 08:01 AM   #414
regal is offline regal  United States
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Quote:
Originally Posted by s3tup View Post

Regal, these suggestions are from HtP, he is somehow related to Phillips:
TDA1541 info
Nice read...
So you see that there should be a cap from -15V to -5V (close to the chip), so the internal 10V reference is as good as possible ?
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Old 11th March 2012, 09:58 AM   #415
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by s3tup View Post
Thorsten,
Do you refer to lack of:
- DEM clocking,
- I2S attenuation
- I2S reclocking
- Shunt regs
Non of the above.

If you do not use any proper re-clocking and no DEM re-clocking and no I2S attenuators or shunt regulators, this is a choice, though it is severely suboptimal in itself.

I am referring to the power supply arrangements (as there is little else on the board) where you reserve the worst regulator for the moist sensitive voltage and your valiant attempt to maximise jitter resulting from the interconnection between source (Digital Filter) and DAC Chip.

Quote:
Originally Posted by s3tup View Post
I'm well aware of these. I2S things will be on digital board
Really. And you REALLY think this is a good idea? Especially with a ribbon cable connection to the TDA1541 and the impedances involved?

Of course there many ways skinning digital cat's. I just see in your design about all the various ways in which to get thing wrong faithfully implemented and what may seem a deliberate rejection of all the good information available about how the TDA1541 works, about how digital connections with known impedance connections can be optimised, etc., et al.

Anyway, you have fun your way.

However, do me one favour. If you find the results of your efforts to be less than good at delivering the sound quality you expect, do not blame the TDA1541, but the designer.

Ciao T
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Old 11th March 2012, 11:43 AM   #416
regal is offline regal  United States
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I'm not getting the ribbon cable comment, I've seen a lot of higher end DAC (albeit not tda1541) where the input section is a separate board with small (1") jumpers connecting I2S to the main board. Is impedance mismatch an issue with a tiny jumper?
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Old 11th March 2012, 12:30 PM   #417
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by regal View Post
I'm not getting the ribbon cable comment, I've seen a lot of higher end DAC (albeit not tda1541) where the input section is a separate board with small (1") jumpers connecting I2S to the main board. Is impedance mismatch an issue with a tiny jumper?
If the cable is short enough it's characteristic impedance will not matter.

How much is "short enough", depends on a LOT of factors, mostly risetime.

In general I would suggest not running digital audio through those kind of cables without taking care of impedance matching and other factors.

Ciao T
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Old 11th March 2012, 04:26 PM   #418
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Thorsten, thanks for constructive critics! That's what i'm looking for when i post some PCBs/etc.
I hate "i won't comment 'coz i don't want to be mean on poor silly DIYer for his work".
Rough, plain comments are welcome! As long as they are constructive...

I wrote severeal different posts but decided to delete em. They weren't constructive, and were theorized too much Hands-on is the best.
I'll make veroboard rig with current-sense resistors everywhere to investigate 1541 behaviour.
I know i won't get nice THD plots, but at least i'll know where the current flows, it's shape, and what affects it.
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Old 11th March 2012, 04:55 PM   #419
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Hi,

Quote:
Originally Posted by s3tup View Post
I'll make veroboard rig with current-sense resistors everywhere to investigate 1541 behaviour. I know i won't get nice THD plots, but at least i'll know where the current flows, it's shape, and what affects it.
Excellent. I did that once as well. It is important to know where current flows.

There are articles that cover most of the TDA1541 internals. Personally I have some papers (over 100 pages) that originally where Philips internal and go into even bigger detail, but they are in storage and I never scanned them.

The other part is pretty common sense. I would use a re-clocker close to the DAC (ANY DAC, not just 1541) and make sure the only current flowing in the digital ground plane between DAC and reclocker are the return currents of the signal (no supply currents etc.).

Reclockers themselves can have a fair bit of ground bounce which needs to be considered. If the MCK/Reclock Clock cannot be local I would look seriously at how we transmit it and what loading we have on the line.

PERSONALLY I would use 75R Micro Coax with correct connectors for the clock and make sure to back terminate it (if necessary use a discrete clock driver on the sending side) if it is on a separate PCB.

If having the clock on the same PCB look at rise times and consider a back-terminated strip-line.

The "big deal" with the reclocker is that gives you much more control over the whole affairs and allows you to get the jitter at the DAC to be VERY CLOSE to that of your clock.

Now if your clock is horrible bad it will not help, but if you have significant distance between source and maybe poorly terminated ribbon cables with a decent clock (say a Wolfson Micro Receiver well implemented) it can make a big difference...

BTW, I would seriously sync DEM clock and wordclock at integer multiples of four or more for the DEM Clock to wordclock ratio.

As I pointed out earlier, using the re-clocker I suggested (74...175) offers differential outputs, which incidentally can help with the ground bounce if loaded equally, so dealing with the DEM reclocking becomes easy...

Ciao T
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Old 11th March 2012, 07:12 PM   #420
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Sadly, no. But Robert Deutsch and Art Dudley will be representing Stereophile at the 2012 SSI and reporting live.

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