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julian  
#1 Posted : Thursday, October 14, 2010 6:38:11 AM(UTC)
julian

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Hi,

I am just testing my COD module. I decided to quickly solder in the resistors to use the integrated passive resistive I/V state. Am I right that I should be able to measure the output signal between GND and L+ respectively GND and R+ then?
Because so far I only get a constant voltage of 1.4V on right channel and 1.6V on left channel.
Measuring GND to L-/R- gives 2.6V

Thanks,

Julian
Brian Donegan  
#2 Posted : Thursday, October 14, 2010 6:41:03 AM(UTC)
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Did you add the output capacitors as well? They are there to block the DC.
julian  
#3 Posted : Thursday, October 14, 2010 6:48:59 AM(UTC)
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Yes, the four capacitors are in there.
julian  
#4 Posted : Thursday, October 14, 2010 2:00:22 PM(UTC)
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One more note: I have to COD modules and I just connected the second module. Just with +7.5V VCC and GND. Having Va bridged to Vd.
Nothing else connected and I see the same dc voltages at the outputs.
Is this expected?
julian  
#5 Posted : Friday, October 15, 2010 11:04:39 AM(UTC)
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Ok, I recognized, that it would be a good idea to have a load on the outputs when trying to measure. So I added 10k between each output and GND. So now the output after the caps is 0V.
Measuring across the 4 resitors I have 2.6V on each - all the time. No matter what I do input to the DAC.
Another note: The ZERO pin behaves as expected. When no signal is input it is HIGH. As soon as I start to write to the DAC it becomes LOW.

Regards,
Julian
Brian Donegan  
#6 Posted : Friday, October 15, 2010 11:07:19 AM(UTC)
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This sounds perfectly normal.
julian  
#7 Posted : Friday, October 15, 2010 11:13:13 AM(UTC)
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Well what does not sound perfectly normal, is that the output stays 0 even when there is I2S input.
You can see a capture of my I2S signal (1kHz Sine wave on right channel) here:
http://jusst.de/files/i2s_plot2.png

The signal-lines have 5V peak, the data line (blue) only 3.4V - which both is in the range the PCM1794a should accept.
BCLK is 1,536MHz
LRCLK is 48kHz

Any thoughts, what might be wrong then?
Brian Donegan  
#8 Posted : Friday, October 15, 2010 11:21:26 AM(UTC)
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You should 0VDC on the outputs, but varying VAC with music playing. Can you hear music?
julian  
#9 Posted : Friday, October 15, 2010 12:36:08 PM(UTC)
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Sorry, ouput AC is 0V a well - so no signal.
I have no loudspeaker connected, only measuring with the scope so far... But I really should be able to see a +/-1.8V with the scope.
I may try the second module I have, to be sure the DAC is not defect. But I would be rather surprised if it was...

Any other ideas?
Erlend Sæterdal  
#10 Posted : Monday, November 28, 2011 2:38:33 PM(UTC)
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Brian Donegan wrote:
Did you add the output capacitors as well? They are there to block the DC.


???????? What DC ? I do not understand it is a Current output dac so why is the caps needed ?
Brian Donegan  
#11 Posted : Monday, November 28, 2011 2:45:54 PM(UTC)
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Originally Posted by: Erlend Sæ Go to Quoted Post
Brian Donegan wrote:
Did you add the output capacitors as well? They are there to block the DC.


???????? What DC ? I do not understand it is a Current output dac so why is the caps needed ?


When the passive I/V resistors are installed, it becomes voltage out...
Russ White  
#12 Posted : Monday, November 28, 2011 2:52:55 PM(UTC)
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Are you passing in the master(system) clock?
Erlend Sæterdal  
#13 Posted : Monday, November 28, 2011 4:11:39 PM(UTC)
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Brian Donegan wrote:
Originally Posted by: Erlend Sæ Go to Quoted Post
Brian Donegan wrote:
Did you add the output capacitors as well? They are there to block the DC.


???????? What DC ? I do not understand it is a Current output dac so why is the caps needed ?


When the passive I/V resistors are installed, it becomes voltage out...


Thank you that explains what just happened.
Erlend Sæterdal  
#14 Posted : Tuesday, December 27, 2011 11:45:53 AM(UTC)
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Is the caps needed when a Legato II is used ? I/V resistors is 360 ohm and at the opamp all the resistors are 1,5 kohm.
Russ White  
#15 Posted : Tuesday, December 27, 2011 11:48:15 AM(UTC)
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When using Legato you would use jumpers instead of AC coupling caps and no I/V resistors on the COD itself.
Erlend Sæterdal  
#16 Posted : Tuesday, December 27, 2011 2:44:20 PM(UTC)
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Thank you very much.
Another place you recommended 357 ohm on the cod board and 1,5 kohm around the opamp.
Russ White  
#17 Posted : Tuesday, December 27, 2011 4:18:17 PM(UTC)
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Link? I think what I actually said was 357 at the I.V spots on the legato, and 1.5K at the CCS spots.
Erlend Sæterdal  
#18 Posted : Tuesday, December 27, 2011 10:42:44 PM(UTC)
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Russ White wrote:
Link? I think what I actually said was 357 at the I.V spots on the legato, and 1.5K at the CCS spots.


Sorry I do not understand anything I.V spots and CCS spots ?
Erlend Sæterdal  
#19 Posted : Tuesday, December 27, 2011 10:53:33 PM(UTC)
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Originally Posted by: Erlend Sæ Go to Quoted Post
Russ White wrote:
Link? I think what I actually said was 357 at the I.V spots on the legato, and 1.5K at the CCS spots.


Sorry I do not understand anything I.V spots and CCS spots ?


Ok I know I.V spots is R1 -R4 and CCS spots is R 9-16 . Boo hoo!
Erlend Sæterdal  
#20 Posted : Tuesday, December 27, 2011 11:13:39 PM(UTC)
Erlend Sæterdal

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Originally Posted by: Erlend Sæ Go to Quoted Post
Originally Posted by: Erlend Sæ Go to Quoted Post
Russ White wrote:
Link? I think what I actually said was 357 at the I.V spots on the legato, and 1.5K at the CCS spots.


Sorry I do not understand anything I.V spots and CCS spots ?


Ok I know I.V spots is R1 -R4 and CCS spots is R 9-16 . Boo hoo!


BUT .......... on the Legato 1.02 schematic R 9-16 is around the opamps . On the 3.01 R 9- 16 is at the bottom at the I/ V circuit.

So on the Legato 2 I shall change the R 20 - 27 Resistors to 1.5 kohm and the 150 ohm. resistors at the top to 360 ohm. Am I right ?

Even more confusion my Legato for the PCM 1794 is a 1.0.3 Version. Anyway the resistors around the opamp shall not be changed . Its only the resistors at the top and bottam of the I/V circuit.

Edited by user Tuesday, December 27, 2011 11:22:35 PM(UTC)  | Reason: Not specified

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