Drive NOS AD1865/62,PCM1704/02/63,TDA1541 from FIFO: Universal I2S-PCM driver board - Page 21 - diyAudio
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Old 12th January 2013, 10:20 PM   #201
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Default TDA1541 offset binary solution, please confirm

1. “Offset binary may be converted into two's complement by inverting the most significant bit.” So, to get an offset binary data format on both DL and DR which were two's complement format, I just need invert the MLB if the corresponding jumper is set for TDA1541. Is that OK?

2. To run NOS DAC’s at differential mode, we need a group of the reversed left and right data. For an I2S format (which is two’s complement), this usually can be done by just inverting the data line.
So, nDL=~DL; nDR=~DR;
The only problem is that will result in adding 1 LSB DC offset on the DAC output. Because the real reversed data should be equle to ~data +1.
Is there any problem on the 1 LSB DC offset? Or, it’s not an issue?

3. Method 2 will apply to data in offset binary format the same way as two’s complement to get the reversed data.

If all answers are yes, the offset binary mode would be no difficult to achieve.

Ian
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Last edited by iancanada; 12th January 2013 at 10:28 PM.
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Old 14th January 2013, 08:53 AM   #202
noizas is offline noizas  Lithuania
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Default TDA1541 offset binary solution

Quote:
Originally Posted by iancanada View Post
1. “Offset binary may be converted into two's complement by inverting the most significant bit.” So, to get an offset binary data format on both DL and DR which were two's complement format, I just need invert the MLB if the corresponding jumper is set for TDA1541. Is that OK?

2. To run NOS DAC’s at differential mode, we need a group of the reversed left and right data. For an I2S format (which is two’s complement), this usually can be done by just inverting the data line.
So, nDL=~DL; nDR=~DR;
The only problem is that will result in adding 1 LSB DC offset on the DAC output. Because the real reversed data should be equle to ~data +1.
Is there any problem on the 1 LSB DC offset? Or, it’s not an issue?

3. Method 2 will apply to data in offset binary format the same way as two’s complement to get the reversed data.

If all answers are yes, the offset binary mode would be no difficult to achieve.

Ian
Hi Ian,

thank you for your time and efforts used for such DIY gems.

In my humble opinion inverted I2S or offset binary stream for differential TDA1541 DAC is ok.
Because 1 LSB DC offset is permanent and really small (about 60nA),
such DC offset can be simply ignored, especially in cases if there are 2mA current injection circuits on the TDA1541 outputs.
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Old 14th January 2013, 11:41 AM   #203
erin is offline erin  Australia
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Most circuits have compromises of one sort or another. In this situation we have to accept a little DC offset for (IMO) reduced jitter. I don't think its a problem. But looking forward to these boards.
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Old 15th January 2013, 03:17 AM   #204
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Hey all.
Quick question about using this with a PCM1704.

As PCM1704 kits are few and far between, are there any DACs out there that are easy enough to modify to incorporate this driver (as well as the reclock kit) ? There are a few "cheap" dacs on ebay, as well as the audio-gd dacs, all in the sub $1000 bracket.

Last edited by lordvader; 15th January 2013 at 03:23 AM. Reason: replace audio-dedign with audio-gd
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Old 15th January 2013, 08:21 AM   #205
erin is offline erin  Australia
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If you already have a PCM1704 DAC you could use this board to replace your oversampling filter.
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Old 15th January 2013, 09:20 AM   #206
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What about a good I/V stage for the 1704? Now that Mr.Borbely is no longer providing kits what would be a good(read best ever) option? Asking because Peter who created the Phasure NOS1 DAC once said that you must die a thousand deaths to make it right and has stuck in my head paralyzing me to make a decision...
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Old 15th January 2013, 10:58 AM   #207
regal is offline regal  United States
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Quote:
Originally Posted by iancanada View Post
1. “Offset binary may be converted into two's complement by inverting the most significant bit.” So, to get an offset binary data format on both DL and DR which were two's complement format, I just need invert the MLB if the corresponding jumper is set for TDA1541. Is that OK?

2. To run NOS DAC’s at differential mode, we need a group of the reversed left and right data. For an I2S format (which is two’s complement), this usually can be done by just inverting the data line.
So, nDL=~DL; nDR=~DR;
The only problem is that will result in adding 1 LSB DC offset on the DAC output. Because the real reversed data should be equle to ~data +1.
Is there any problem on the 1 LSB DC offset? Or, it’s not an issue?.


Yes it is a problem, must run two's compliment at 32fs, see original 16 bit Phillips I2S standard. Makes a CD a 15 bit system which is already "hurting" for resolution. (See the other place for a good discussion about the issue.)

Last edited by regal; 15th January 2013 at 11:07 AM.
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Old 15th January 2013, 11:05 AM   #208
regal is offline regal  United States
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Quote:
Originally Posted by Nikola Krivorov View Post
What about a good I/V stage for the 1704? Now that Mr.Borbely is no longer providing kits what would be a good(read best ever) option? Asking because Peter who created the Phasure NOS1 DAC once said that you must die a thousand deaths to make it right and has stuck in my head paralyzing me to make a decision...
Here you can still buy Erno's I'V stage, but its really just a discrete opamp.
LB-437IVL - A WebsiteBuilder Website.

There are many other solutions and opinions, Euvl on here has a good one called the Sen.

I like simply passive I/V + jfet or tube gain (w/filtering.).
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Old 15th January 2013, 01:03 PM   #209
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Quote:
Originally Posted by regal View Post
Yes it is a problem, must run two's compliment at 32fs, see original 16 bit Phillips I2S standard. Makes a CD a 15 bit system which is already "hurting" for resolution. (See the other place for a good discussion about the issue.)
regal,

The I2S to PCM daughter board will precess and output data in true 16bit word format if you set the jumper for TDA1541.

The 1 LSB DC offest issue is only connected with data reversing for differential mode or dual mono mode. To reverse the data, it will invert all bits within a word.
I didn't see the reversing has anything to do with 32/16 bit word length issue.

Let me know what your are concerned about.

Regards,

Ian
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Last edited by iancanada; 15th January 2013 at 01:06 PM.
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Old 16th January 2013, 12:22 PM   #210
regal is offline regal  United States
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Quote:
Originally Posted by iancanada View Post
regal,

The I2S to PCM daughter board will precess and output data in true 16bit word format if you set the jumper for TDA1541.

The 1 LSB DC offest issue is only connected with data reversing for differential mode or dual mono mode. To reverse the data, it will invert all bits within a word.
I didn't see the reversing has anything to do with 32/16 bit word length issue.

Let me know what your are concerned about.

Regards,

Ian
I see what you mean know. Couldn't you convert from i2s to two's compliment at 32 bit then truncate down to 16 bit, that way the LSB would be preserved ?

There are three advantages to 2's compliment with the tda1541a:
1. dual differential
2. dual mono
3. 8xfs (prior to fifo).

Any of three would be negated should we lose the LSB, so I guess I am in the all or nothing camp as far as two's compliment conversion for tda1541 goes (its a touchy subject for many.)

You wouldn't want your design to be less than the best if it is offering this mode I think. The TDA1541A's LSB is its claim to fame in a way, it was developed at a time when there were only 14 bit DAC's, and phillips did a huge amount of engineering to get that 16 bit resolution to match a RBCD standard. Best not offer it on this design if its only 15 bit resolution maybe rev 2 things will fall into place, just my opinion.
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