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Building the ultimate NOS DAC using TDA1541A
Building the ultimate NOS DAC using TDA1541A
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Old 15th November 2018, 07:37 AM   #6771
levelUP is offline levelUP
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Join Date: Dec 2016
Hi, John
I read this forum since the very beginning. Thank you for sharing you brilliant ideas with us.
Sorry for offtopic, but I have few questions. I planing to build dac with pcm1704, can I use smaller film coupling capacitors in analog part, lets say 10-20uf wima instead of 50uf or 20-40uf insted of 100uf BPO DC? I will use LT3045 voltage regulators Click the image to open in full size.
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Old 17th November 2018, 05:12 AM   #6772
Alexandre is offline Alexandre
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John, thanks for the excellent info, as always.

It makes perfect sense: tda1543 is very sensitive to clocking method and jitter, tda1545 and 1387 less so. The latter use "symmetric offset decoding", which is similar to sign magnitude / segmented summing. BTW, the ad1862 is also done this way.

Thanks,
Alex

Quote:
Originally Posted by ecdesigns View Post
The zero order hold output signal of a DAC in combination with timing fluctuations can lead to a PWM effect where the energy level (v * i * t) of each sample can fluctuate so we could end up with timing related bit errors. The higher the weight of the bit, the more impact a given timing fluctuation will have. As long as we don't use any of the MSBs for low level generation we would be fine ..... oh we do use the MSBs for low level generation (MSB trimming remember?).

No wonder we have jitter issues with D/A converters that use the MSBs for low level signal generation.

If we would only use the bits we actually need (only the LSBs for low level signal generation) the audible impact of jitter on a zero order hold signal would be far less.

Last edited by Alexandre; 17th November 2018 at 05:17 AM.
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Old 17th November 2018, 07:46 AM   #6773
batteryman is offline batteryman  United Kingdom
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Quote:
Originally Posted by Alexandre View Post
. BTW, the ad1862 is also done this way.
Thanks,
Alex
The AD1862 does not mention Sign Magnitude data format.
It states:

"A serial 20-bit, 2s complement data word is clocked into
the DAC, MSB first, by the external data clock."

So is the conversion done internally?
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Old 17th November 2018, 08:44 AM   #6774
ecdesigns is offline ecdesigns  Netherlands
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Hi batteryman,

Quote:
The AD1862 does not mention Sign Magnitude data format.
It states:

"A serial 20-bit, 2s complement data word is clocked into
the DAC, MSB first, by the external data clock."

So is the conversion done internally?
AD1862 Datasheet page 5

quote:

The design of the AD1862 uses a combination of segmented decoder, R-2R topology and digital offset to produce low distortion at all signal amplitudes. The digital offset technique shifts the midscale output voltage (0 V) away from the MSB transition of the device. Therefore, small amplitude signals are not affected by an MSB change. An extra DAC cell is included to avoid clipping the output at full scale.
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Old 17th November 2018, 08:54 AM   #6775
batteryman is offline batteryman  United Kingdom
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Quote:
Originally Posted by ecdesigns View Post
Hi batteryman,
AD1862 Datasheet page 5
quote:

The design of the AD1862 uses a combination of segmented decoder, R-2R topology and digital offset to produce low distortion at all signal amplitudes. The digital offset technique shifts the midscale output voltage (0 V) away from the MSB transition of the device. Therefore, small amplitude signals are not affected by an MSB change. An extra DAC cell is included to avoid clipping the output at full scale.
Thanks, I did read that but I didn't think of it as the dac having in effect, converted the TWC input to SM.
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Old 17th November 2018, 10:07 PM   #6776
maxlorenz is offline maxlorenz  Chile
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Quote:
Originally Posted by hopkins View Post
I have the UV as well (great DAC) so I'll answer - yes, you can hear small clicks when you use the build in volume control, whether through the remote or through software control.

Best
Thanks!
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Old 21st November 2018, 02:04 PM   #6777
batteryman is offline batteryman  United Kingdom
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Quote:
Originally Posted by batteryman View Post
Koldby, tried your suggestion of bypassing Ian's board for WS - no difference to the distortion.

Next connected the board to a cheap USB to I2S interface.
Screen shots attached. Still looks like one of the clock cycles is after the rising edge of LE but no distortion heard from Youtube so far. (48Khz)

Does this mean that the I2S data from the Denon Cd player is not actually I2S?

Images: Bck + L, D + BCK, D + L
I can now answer my own question!

Yes, its 16bit right justifed MSB first. (which explains the distortion although I am surprised I got any audio at all).

To find this out, I installed a sample rate converter evaluation board - a SRC4192 in my dac and connected it to the AD1862 dac board from DIYINHK. (I2S in)

I set the output to I2S and the input to 16bit RJ, and this was the only setting that worked with the dac. (I tried all the other input data formats - I2S, 24bit LJ, 18,20, 24bit RJ)

Taking Marcelvg's advice, I set the 4192's clock generator for 24.576Mhz which gave an output bit clock of about 6.14Mhz and fs of 96k (clock/256) & 20bit compared to the input data of 16bit, 44k/2.822M.

The sound quality is nothing special, with occasional quiet clicks - like a worn LP, but I have not found the cause. Its probably due to the wiring between CD player and dac & maybe the ADUM digital isolator between them or maybe the SRC4192 itself.

This doesn't matter for now as I will be using the AD1820 with a USB to I2S converter and building a second dac powered entirely by Lifepo4 & Lipo cells
using IanCanadas Fifo II and I2S board plus my own balanced TDA1541 dac board.

So I feel a clot for accidentally feeding Ian's I2S board with the wrong data type but in my defence, no one came up with a definitive answer as to what the actual data format was.
You 'live & learn'.
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Old 22nd November 2018, 03:25 PM   #6778
xaled is offline xaled
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Quote:
Originally Posted by lcsaszar View Post
Alternatively, my DAC linearity test CD that I mentioned several post ago could be used. It toggles LSB at each bits on three DC levels (bit n-LSB, bit n, bit n+LSB). If LSB is missing, you will see only two DC levels.
Just validated the bit perfectness of rpi with moode player set to generic hifibery dac using test tracks from lcsaszar and it looks good:

Track1:
i2s-hifyberry.png

Track2:
i2s-hifyberry-2.png
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Old 22nd November 2018, 09:45 PM   #6779
xaled is offline xaled
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Now I'm trying to find the right settings to have left justified output format on rpi.
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Old 25th November 2018, 11:22 AM   #6780
koldby is offline koldby  Denmark
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Quote:
Originally Posted by batteryman View Post
I can now answer my own question!

Yes, its 16bit right justifed MSB first. (which explains the distortion although I am surprised I got any audio at all).

To find this out, I installed a sample rate converter evaluation board - a SRC4192 in my dac and connected it to the AD1862 dac board from DIYINHK. (I2S in)

I set the output to I2S and the input to 16bit RJ, and this was the only setting that worked with the dac. (I tried all the other input data formats - I2S, 24bit LJ, 18,20, 24bit RJ)

Taking Marcelvg's advice, I set the 4192's clock generator for 24.576Mhz which gave an output bit clock of about 6.14Mhz and fs of 96k (clock/256) & 20bit compared to the input data of 16bit, 44k/2.822M.

The sound quality is nothing special, with occasional quiet clicks - like a worn LP, but I have not found the cause. Its probably due to the wiring between CD player and dac & maybe the ADUM digital isolator between them or maybe the SRC4192 itself.

This doesn't matter for now as I will be using the AD1820 with a USB to I2S converter and building a second dac powered entirely by Lifepo4 & Lipo cells
using IanCanadas Fifo II and I2S board plus my own balanced TDA1541 dac board.

So I feel a clot for accidentally feeding Ian's I2S board with the wrong data type but in my defence, no one came up with a definitive answer as to what the actual data format was.
You 'live & learn'.
I think I pointed you in that direction in post 6631:
Building the ultimate NOS DAC using TDA1541A
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