AVR With Best Digital Volume Control For Digital Output Mod

[robinasu]

I would like to point out that while a schematic is always very helkpful, it is by no means a requirement if you are familiar with various DAC part numbers or are willing to spend some time with Google in order to identify the DAC on your AVR's DSP board. Datasheets are readily available for almost all DACs.

Thanks for the inspiration, btw. Just need to find some info on some AVR digital volume implementation, so maybe set and forget the modded AVR and find a HDMI-CEC to RS-232 bridge. The meridians have RS-232 control.

 

[robinasu]

The simplest approach in that case would be to make use of a cheap ADAU1701 board such as the APM2 in slave mode. He could feed the I2S clocks and all four data lines directly to it and then out to a few SPDIF encoders. The 1701 would handle digital volume control and has GPIO to spare. At 48KHz, this would introduce only one millisecond of additional latency.

I will look into this option before I pull the trigger on these:

Digital Interface I2S to SPDIF AES EBU XLR 110 Ohm for Amanero WM8805 - Audiophonics

Voici une Interface I2S avec sortie soudable vers une SPDIF 75Ohm (coaxial, BNC) ou AES EBU XLR 110 Ohm

www.audiophonics.fr

Also, need to make sure the candidate AVR doesn't have some custom SOIC for cost saving that integrates the DAC. The Denon AVR-X1700H looks interesting.

 

[robinasu]

Update from my side. I bought some I2S to SPIDIF converter boards and a Denon AVR-X1700H. The converters arrive in a couple months. The Denon arrived today and I was a little concerned about the PCB layout compared to my plans but after some time I think it will be ok. I also found some nice pads around the codec, but haven’t had time to decode them. I haven’t been able to find the datasheet for the codec or AVR; even emailed Denon and they said engineering hadn’t released it yet. Trial and error might be the way forward. I'll probably try to ohm the pads out to the DAC, which is a TI PCM5102A, and I have the pinout.

 

[voodooless]

Nice to see you taking the plunge Looks indeed like the datasheet of the DSP (it's not the codec) is under lock and key for some reason. Possibly another point where you can find the I2S lines is right where the DAC board is. The ribbon cable should carry all the needed signals. With a bit of luck, you can just disconnect it and make some new PCB with the same connector to harvest the signals from. This would be neet solution for such a board (if you need only 6 channels):

- Multichannel I2S connector -> ADAU1701
- uC to listen to I2C interfaces of volume control chips (I assume that they are I2C and with a bit of luck it's on the same connector)
- uC connected to ADAU1701 to control volume based on what the AVR send to it
- ADAU1701 to 3x SPDIF

If one were to adopt various connectors on there (and support for multiple I2C volume control chips), one could make a kit to retrofit various AVRs this way. Might be a nice project

 

[robinasu]

I was hoping it had a good digital volume control, but after the DACs there is an I2C controlled analog volume control IC. My speakers have volume control and RS-232, so I will just try to tap the digital stream and then find a HDMI-CEC to RS232 bridge.

 

[voodooless]

I was hoping it had a good digital volume control, but after the DACs there is an I2C controlled analog volume control IC. My speakers have volume control and RS-232, so I will just try to tap the digital stream and then find a HDMI-CEC to RS232 bridge.

Alternatively, you can use the web interface of the AVR: just have a service scrape the volume, and from there set your speakers to the equivalent volume via serial.

 

[Vincentponcet]

The simplest approach in that case would be to make use of a cheap ADAU1701 board such as the APM2 in slave mode. He could feed the I2S clocks and all four data lines directly to it and then out to a few SPDIF encoders. The 1701 would handle digital volume control and has GPIO to spare. At 48KHz, this would introduce only one millisecond of additional latency.

Volume control at the spdif level, so over 24 bits, will crush the distortion.
A good digital volume control should be done in 32 bits, and using a DAC chip having a 32 bits input, so a digital volume control before an spdif interface is not great.
Or using a DAC chip with integrated digital volume control, like ess dac chips, then even if the input is spdif 24 bits, the volume control is internally made in 32 bits to the Delta sigma modulator.

http://www.esstech.com/files/3014/4095/4308/digital-vs-analog-volume-control.pdf

 

[Weeb Labs]

Volume control at the spdif level, so over 24 bits, will crush the distortion.
A good digital volume control should be done in 32 bits, and using a DAC chip having a 32 bits input, so a digital volume control before an spdif interface is not great.
Or using a DAC chip with integrated digital volume control, like ess dac chips, then even if the input is spdif 24 bits, the volume control is internally made in 32 bits to the Delta sigma modulator.

http://www.esstech.com/files/3014/4095/4308/digital-vs-analog-volume-control.pdf

In the aforementioned scenario, volume control would be handled at 32 bit by the ADAU1701.

 

[Vincentponcet]

In the aforementioned scenario, volume control would be handled at 32 bit by the ADAU1701.

How does it connect to an external DAC chip ?

 

[Weeb Labs]

How does it connect to an external DAC chip ?

Either via I2S or SPDIF.

 

[Vincentponcet]

Either via I2S or SPDIF.

I thought SPDIF only supported 24 bits, and not 32 bits.

 

[Weeb Labs]

I thought SPDIF only supported 24 bits, and not 32 bits.

That is correct. The ADAU1701 can output any required word length but gain control will always be performed internally at 32-bit precision.