ADAU1701

Hello Jefffree,

The ADAU1701 is a DSP with built in stereo ADCs and Quad DACs. There could be many reasons for the noise but I suspect that the DSP is not booting up. I do not know this design if they are using the serial ports to send audio out then back in which means it could be something else internal.

Your measurement of pin 47 is a little high. On my eval board it is 1.7V.

First you need to determine if the DSP has what it needs to function and if it is being properly programmed at power up.

Power:

Pin 18, 34, 36 and 48 should all be 3.3V and look clean.

Pin 13 and 24 should have 1.8V on them.

Pin 35 should have around 1.8V on it. But this depends on the master clock frequency. This is the PLL Loop filter pin.

Pin 41 I am measuring around 1.7V

Pin 40 will be around 1.5V

Take a scope and look at pin 32. It should have the master clock on it and it is most likely 12.288MHz. It can be different so see what you got.

Now on to the communications for booting up.

Pin 22 and 23 are the I2C SDA and SCL. You should be able to see on a scope the transmission from the EEPROM to the DSP when you power up. It is rather quick but the entire DSP program must be loaded in. See if that is happening.

Dave T

Thanks Dave. I measured the voltage at the indicated pins. They correspond to what you indicated, with the exception of pin 47. Oscillation is present. Exchange on the I2C bus is also available, this is evidenced by the correct glow of the LEDs of the PIC processor. In general, the ADAU1701 works as a crossover, the amplifier also works. I also tried to change the firmware. With firmware from the RCF ART 715-A MK2, the amplifier did not work. With the firmware from the RCF ART 315A, the amplifier works, but noise is also heard like a white medium volume. I returned the native firmware to the amplifier. So, the noise problem has not yet been resolved.

Hi Dave!

By replacing the ADAU1701, I found out that the reason for the noise is the wrong voltage at the FILTA terminal 47. Can you tell me why there is an excessive voltage at terminal 47?

Hello Jefffree,

Check the output of the voltage regulator on the eval board. It is U2 and pins 1,2 & 3 are the output. You can also measure it across C23 which is a 10uf cap so it is a little larger and easier to find and probe.

If it is above 3.3V then check R6. It should be 78.7K. Some boards went out with 78 ohm resistors. I thought we had caught all of them but maybe you might have one.

What is the voltage on pin 40? and pin 41?

Thanks,

Dave T

Hello Dave. I do not have an eval board device. I have a biamp RCF ART 715-A MK4. I soldered ADAU1701 to the one that I dropped from this board earlier. After that, the voltage at pin 47 became 1.68 V and the noise became almost inaudible. I hope the problem is solved. Thank you for your help.

Hello Jefffree,

Glad it seems to be OK. This pin is there only to provide a place to filter an internal bias voltage that is generated internally. I have never seen one go bad because there are only small currents involved. I would suspect leakage from contamination on the PCB or a soldering issue? I recently was troubleshooting an old Trident console on the weekend and one channel had issues that were caused by a cap leaking and contaminating the PCB. It was a light oily film but it was enough to cause leakage of current into the reference leg of an Op amp and throw it off to cause lots of distortion.

I hope you got it.

Sorry I answered too quickly earlier without reading the entire post again.

Dave T