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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
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Did you add the output capacitors as well? They are there to block the DC.
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Yes, the four capacitors are in there.
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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?
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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
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This sounds perfectly normal.
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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.pngThe 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?
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You should 0VDC on the outputs, but varying VAC with music playing. Can you hear music?
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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?
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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 ?
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Originally Posted by: Erlend Sæ  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...
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Are you passing in the master(system) clock?
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Brian Donegan wrote:Originally Posted by: Erlend Sæ 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.
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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.
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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.
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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.
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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.
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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 ?
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Originally Posted by: Erlend Sæ 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 . 
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Originally Posted by: Erlend Sæ Originally Posted by: Erlend Sæ 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 . 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)
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