ADAU1701 No sound (input problem)

Hello,

Attach your schematic diagram of your hardware and the SigmaStudio schematic.

Dave T

Board is freeDSP schematic can be found here.

My SigmaStudio schematic is a basic crossover:

Hello,

If you are using default resistor values and if I can believe the schematic there are no resistors connecting to the ADC inputs. R26, R28, R30, R31, R32, and R33 are all listed as "None". I think it is that way so that you can choose what voltage level you need for full scale input to the ADC. Please read the ADAU1701 datasheet's Audio ADC section on page 20 for details on choosing this resistor.

You can obtain the datasheet here: http://www.analog.com/media/en/technical-documentation/data-sheets/ADAU1701.pdf

Dave T

Sorry for missing that, but I have those resitors. They are 18k, 10.5k and 7.15k to match diferent input levels, and are configured via jumpers.

After cheking it out with a scope, I found out that there is a lot of high frequency noise present on the ADC inputs. On one side of input resistors(R26, R28, R30-R33) the signal is beutiful biased audio signal, but on the other side (connected to ADAU1701) there is a lot of noise.

Hello,

This input is a current input so you will not see much signal voltage. There is still 2K of resistance in series with the ADC current input so there will still be a little voltage but not much. It is almost like a virtual earth node of a summing input. The signal is there, it is just in current form not voltage.

Dave T

But as I described earlier, when I accidentally shorted ADC and ADC_RES, I got some sound on the output. And looking with a scope, when I short them, the voltage on the adc pin, becomes closer to the actual signal voltage.