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Hello
I've a issue with the SPDIF output of this Mux, which I send to the input of my Dacmagic. The problem is that the Dacmagic can't detect the signal sended by the mux. I checked it with an oscilloscope, and it measured about 0,5Vpp, while the signal of the CD player or the computer measured about 1Vpp. It seems that the signal is too low for the DAC. Would it possible to raise the output level changing the values of R3/R2?
Thanks
Alberto
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Thank you very much. What resistor should I change, R3, R2 or both? Edit: The measured voltages was wrong. The CD signal measured at the mux input is 0.5Vpp. The mux output is 0.2Vpp, loaded with the DAC. The voltage between C5 and R3 is 2.4Vpp. will it be damaged? Edited by user Sunday, January 2, 2011 3:21:07 PM(UTC)
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I found in a Cirrus application note, 210/107 Ohm when Vl=3.3V. With 75Ohm load, and 2.4Vpp input, the output might be nearly 0.5Vpp What do you think about this values? Thanks. Edited by user Monday, January 3, 2011 7:52:06 AM(UTC)
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Anybody knows the TX output impedance of this chip? With this data, it would be easy to calculate a new voltage divider. Assuming an output impedance about 40Ohm (I can not find this data in the datasheet), 160/120 could be appropiate values. It gives a 75Ohm match for the Z, and 0.53Vpp into 75ohm load. Anyway, Is there any reason why this module outputs this very low voltage? Edited by user Monday, January 3, 2011 8:36:46 AM(UTC)
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I have tested the module with 160/120 and 210/107, and it seems to work fine. The output voltage is still a little low, 0.45Vpp, but enough for my DAC. So, I think that there is a mistake with the default values, they are not suitable for 3.3V operation.
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amr wrote:I have tested the module with 160/120 and 210/107, and it seems to work fine. The output voltage is still a little low, 0.45Vpp, but enough for my DAC. So, I think that there is a mistake with the default values, they are not suitable for 3.3V operation. Ah yes I see the problem. When we initially designed the MUX I think we were looking at 5V for VL. And since it it actually has 3.3V installed we will need to change those R values. Thank for you for spotting this issue. We will correct it. Interesting thing, I just tested mine, and the Buffalo at least has no trouble locking onto the output even at that level.
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Also, those resistor values where the suggested values from Cirrus Logic, but I think they were also assuming 5V VL.
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