Any good TDA1541A DAC kit? - Page 54 - diyAudio
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Old 11th February 2013, 07:47 PM   #531
Ben Mah is offline Ben Mah  Canada
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Quote:
Originally Posted by Ceglar View Post
Thanks, Ben.

The only question I have, how to set 74HC4040 to divide by 8?.

Here is what I plan to try once I know how to set the divider up. Hopefully it resembles accurately everything that has been suggested.

As always, any comments are welcome.

**edit - 74HC4040 CLK is supposed to be BCK and not MCK from the USB > I2S device as drawn.

Regards,
Shane
For the 74HC4040, Q1 is /2, Q2 is /4, Q3 is /8, etc.

Looking at your schematic, I treated the unused inverted outputs of the 74HC175 differently. Instead of sending the outputs to the voltage divider circuit as you have shown, I connected the outputs to inline resistors of the same value as the non-inverted outputs and then to digital ground. As I mentioned previously, this does not take into consideration for the TDA1541a circuitry impedances. I suppose measurements of the current in the inline resistors of the I2S lines could be done by measuring the voltage drop across a resistor in each line to determine the current and then adjust the resistors in the inverted outputs to match the corresponding non-inverted currents. It's a fine tuning thing I think, and I have not done that to my dac (I'm not even sure if what I suggested will work). So the current demand on the inverted outputs may be different than on the non-inverted outputs of the 74HC175 in my dac, but it's probably no worse than not loading the unused outputs at all, and hopefully better.
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Old 12th February 2013, 02:41 AM   #532
Ceglar is offline Ceglar  Australia
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Quote:
Originally Posted by Ben Mah View Post
For the 74HC4040, Q1 is /2, Q2 is /4, Q3 is /8, etc.

Looking at your schematic, I treated the unused inverted outputs of the 74HC175 differently. Instead of sending the outputs to the voltage divider circuit as you have shown, I connected the outputs to inline resistors of the same value as the non-inverted outputs and then to digital ground. As I mentioned previously, this does not take into consideration for the TDA1541a circuitry impedances. I suppose measurements of the current in the inline resistors of the I2S lines could be done by measuring the voltage drop across a resistor in each line to determine the current and then adjust the resistors in the inverted outputs to match the corresponding non-inverted currents. It's a fine tuning thing I think, and I have not done that to my dac (I'm not even sure if what I suggested will work). So the current demand on the inverted outputs may be different than on the non-inverted outputs of the 74HC175 in my dac, but it's probably no worse than not loading the unused outputs at all, and hopefully better.

Thanks again.

Using your idea to measure volt drop across the series R to get a value for load currents, if we then bias the unused outputs to the same voltage level (so 1.2V for 1/DATA, 1/WS and 1.2V for 1/BCK), a value of resistance to ground can be selected, which would have the unused outputs at the same voltage potential and with the same load currents as the used outputs.

Do you think there is any switching noise associated with these unused outputs that we dont want going to digital ground?. I note he has the inductor in the BCK voltage divider to stop something along these lines getting back into the 5V supply. It might be worth doing the same with the series resistor from 1/BCK to ground?

**(edit) 1.1V for 1/BCK

Regards,
shane

Last edited by Ceglar; 12th February 2013 at 02:59 AM.
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Old 12th February 2013, 04:39 AM   #533
Ben Mah is offline Ben Mah  Canada
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Quote:
Originally Posted by Ceglar View Post
Thanks again.

Do you think there is any switching noise associated with these unused outputs that we dont want going to digital ground?. I note he has the inductor in the BCK voltage divider to stop something along these lines getting back into the 5V supply. It might be worth doing the same with the series resistor from 1/BCK to ground?

**(edit) 1.1V for 1/BCK
I really don't know if switching noise would be an issue or not. What is definitely important is paying attention to the return paths. What I have done on my dac is keep the paths from inverted outputs to ground of the chip as short and as direct as possible.

Thorsten and others have emphasized the importance of paying attention to supply loops and signal loops, to keep them small and to keep them from crossing or overlapping. His and other people's advice on locations of power supplies relative to signal paths, and placement of chips etc. to minimise sizes of supply loops and signal loops should be followed.
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Old 12th February 2013, 07:53 AM   #534
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That I2S attenuator could (should) be impedance matched to the driven track on the PCB
That's the proper way of doing it.
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Old 12th February 2013, 08:06 AM   #535
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yes yes
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Old 15th April 2013, 03:00 AM   #536
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Question PCBs

Quote:
Originally Posted by vanofmonks View Post
Here is one based on Thorsten's 2005 schematic. The inductors are panasonic with mu metal shields. To save board space, output capacitors are external of the board.

I am extremely interested in your TDA1541A PCB board along with the Thorsten's tube stage board. Have you finished the designed stage and have the PCBs? What are the prices?

Also, at what point you are joining the digital ground to analog ground? I vaguely remember Thorsten recommended to keep two grounds separate and only joining them at one point, i.e. under pin 5.
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Old 15th April 2013, 04:12 AM   #537
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Yes what has happened with this ?
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Old 27th April 2013, 12:12 PM   #538
Aronier is offline Aronier  Germany
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Me too interested?

regards
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Old 27th April 2013, 12:35 PM   #539
regal is offline regal  United States
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Old 27th April 2013, 01:29 PM   #540
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