Another TDA1541A based dac (dual differential) - Page 2 - diyAudio
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Old 7th July 2011, 05:12 PM   #11
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For what reason?

In general, it is highly debateable whether there is an advantage in a differential setup anyway.
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Old 7th July 2011, 05:33 PM   #12
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Quote:
Originally Posted by Tazzz View Post
You don't get all the benefits from running differential if you do it that way you really should split up the I2S into left and right and use separate dacs for the different channels.
Yes, I was thinking that way might be worth trying. I might try both ways and see if I can hear the difference although I can't quite see why splitting them as you suggest gives a benefit.
Perhaps you could explain in more detail.
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Old 7th July 2011, 08:38 PM   #13
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Doing it with one dac for each channel simplifies layout issues pertaining to making the signals equal and opposite and it allows one to resolve current loops locally and/or make opposite currents sum to zero which also helps minimizing unwanted potential differences from currents flowing where they should not.

Also if you look at a -60db 1Khz spectra of a 1541 you will notice that one channel usually measures worse and that this is usually tied to the same channel even between different dacs. Running one dac with inverted data would compound this error.

And there is also that that any time difference between when the different dacs latch out a new sample would translate into a level error at the output.

Last edited by Tazzz; 7th July 2011 at 08:42 PM.
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Old 7th July 2011, 08:47 PM   #14
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Quote:
Originally Posted by Tazzz View Post
Doing it with one dac for each channel simplifies layout issues pertaining to making the signals equal and opposite and it allows one to resolve current loops locally and/or make opposite currents sum to zero which also helps minimizing unwanted potential differences from currents flowing where they should not.

Also if you look at a -60db 1Khz spectra of a 1541 you will notice that one channel usually measures worse and that this is usually tied to the same channel even between different dacs. Running one dac with inverted data would compound this error.

And there is also that that any time difference between when the different dacs latch out a new sample would translate into a level error at the output.
Agree.

But why use two dacs in the first place?
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Old 7th July 2011, 09:45 PM   #15
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It cancels out even order harmonics the 1541a benefits greatly from this. With a differential implementation the -60db 1Khz spectra really looks very very good, even compared to the previous 1541a based dac I had which was not bad.

Listening with a good 1541a and the gain turned up that -60db signal still sounds like pure sine.
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Old 7th July 2011, 09:52 PM   #16
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Quote:
Originally Posted by Tazzz View Post
It cancels out even order harmonics the 1541a benefits greatly from this. With a differential implementation the -60db 1Khz spectra really looks very very good, even compared to the previous 1541a based dac I had which was not bad.

Listening with a good 1541a and the gain turned up that -60db signal still sounds like pure sine.
Mmmmm... Interesting. Can you attach a picture of the fft you refer to?
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Old 8th July 2011, 07:47 AM   #17
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Quote:
Originally Posted by Tazzz View Post
Doing it with one dac for each channel simplifies layout issues pertaining to making the signals equal and opposite and it allows one to resolve current loops locally and/or make opposite currents sum to zero which also helps minimizing unwanted potential differences from currents flowing where they should not.

Also if you look at a -60db 1Khz spectra of a 1541 you will notice that one channel usually measures worse and that this is usually tied to the same channel even between different dacs. Running one dac with inverted data would compound this error.

And there is also that that any time difference between when the different dacs latch out a new sample would translate into a level error at the output.
Thanks, that make sense so will do it that way.

I
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Old 8th July 2011, 08:34 AM   #18
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You could also argue that the added logic would introduce jitter which may have a more detrimental effect than the benefits of such a setup....

I considering a balanced setup myself, but yet need to be convinced of its merits
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Old 8th July 2011, 08:55 AM   #19
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Originally Posted by studiostevus View Post
You could also argue that the added logic would introduce jitter which may have a more detrimental effect than the benefits of such a setup....

I considering a balanced setup myself, but yet need to be convinced of its merits
The Audio Note Dacs* split the data into L & R for the AD1865 dac which doesn't have I2S input, using a 74xx02 and they aren't known for having jitter problems.

(*nos design - Cs8414 input )

In my case, the Sowter I/V transformer is designed for differential input so there is not really any extra complexity other than a 74hct02 and the 2nd 1541.
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Old 8th July 2011, 01:34 PM   #20
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Quote:
Originally Posted by studiostevus View Post
You could also argue that the added logic would introduce jitter which may have a more detrimental effect than the benefits of such a setup....

I considering a balanced setup myself, but yet need to be convinced of its merits
A simplistic view would be (using a 1541 per channel as Tazzz recommends) and considering one channel:
Inputs: L & -L (-L = L data inverted)
Ouputs L + noise and -L + noise.

Subtract in a bifilar wound I/V transformer (swap start and end of one winding to achieve this) results in:
L- -L = 2L and because the noise was added within the dac,
noise - noise = no noise (well, less noise!)

On a separate subject:
What are the consequences of inserting an LC filter with an f-3 of about 15-16kHz* between the 1541 outputs and I/V transformer?

As the impedance needs to kept very low, use of an inductor should be practicable. (Sowter suggest a 200R load resistor on the dac output)

*my ancient ears probably don't work above 12-15KHz!
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