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Old 3rd July 2011, 10:46 PM   #1
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Default Digital Pre-Out

Hello Dear Digital Line lovers,

I am considering adding a "Digital Pre-Out" connector on those A/V receivers :

Denon AVR-1912
Pioneer VSX-1012-K
Onkyo TX-NR690

The idea is to to hook an external 8-channel DAC, possibly a digital crossover also, on the front-left and front-right channels, still retaining the volume control function from the A/V receiver remote control. Possiby adding a low jitter clock recovery block. This way a "Red Book" CD and a SACD may be rendered using an external digital 3-way crossover, using audiophile DACs and using audiophile power amplifiers. As free bonus, when listening to a multichannel source like a Blu-ray, the same audiophile elements will be working.

Proposed HDMI "Digital Pre Out" pinout
****************************
01 TDM/I2S0_Tx
02 I2S1_Tx
03 I2S2_Tx
04 I2S3_Tx
05 TDM/I2S0_Rx
06 TDM/I2S_BitClock
07 TDM/I2S_Fs
08 TDM/I2S_MasterClock
09 TDM/I2S_SHIELD
10 SPI_Mosi
11 SPI_Miso
12 SPI_BitClock
13 SPI_Cs1
14 SPI_Cs2
15 SPI_Cs3
16 SPI_Cs4
17 SPI_SHIELD
18 GROUND

Proposed Mini-USB "Digital Pre Out" pinout
*******************************
only required in case the A/V receivers uses I2C as DAC control
01 I2C_Scl
02 I2C_Sda
03 I2C_Ground
04 I2C_+5V

Is this feasible ? I don't think so. There are going to be crosstalk issues with the HDMI cable.

What would be the complexity of a project taking all the above signals inside the A/V receiver, encoding them into a 100Mbit/s Ethernet II MAC frame synchronized on the audio sampling frequency ? This way the "Digital Pre-Out" would use a RJ45 connector on CAT5 cabling. There would be a tiny PCB containing an Ethernet microcontroller as frame encoder into the A/V receiver, and another tiny PCB containing an Ethernet microcontroller as frame decoder int the external DAC or possibly digital crossover.

The add-on to be executed by duly trained & experienced people. Possibly without losing the manufacturer's warranty.

A "Digital Pre-Out" equipped A/V receiver would have NO functionality changes. Such A/V receiver would continue working EXACTLY as usual. The add-on is only about copying digital signals and bringing them outside in a compact easy transportable form which are 100 Mbit/ Ethernet frames occuring at Fs.

Therefore, if the external audiophile DAC hooked on the "Digital Pre-Out" is only dealing with the front-left and front-right signals, the A/V receiver internal DACs and amps would still be used for delivering the center, subwoofer and rear channels.

The Pioneer VSX-1012-K A/V receiver looks cool :
Videos - Free video downloads and streaming video - CNET TV
You can control it from a Logitech Harmony, a smartphone or a tablet.

Steph
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Old 3rd July 2011, 11:37 PM   #2
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DSD signals also need to be outputted. This is a difficulty. See attached Pioneer VSX-1012-K schematics.
Actually, what is the DSD bitrate per audio channel in the Pioneer VSX-1012-K ?
Attached Images
File Type: jpg Pioneer VSX-1012-K .jpg (406.8 KB, 124 views)
File Type: jpg AK4383.jpg (181.8 KB, 119 views)
File Type: jpg AK4382.jpg (115.0 KB, 113 views)

Last edited by steph_tsf; 3rd July 2011 at 11:42 PM.
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Old 5th July 2011, 07:16 PM   #3
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Look for schematics of Denon AVR-3805 and DVD-2930... Their DenonLinkIII connection requires a CAT5E cable (for pairs - three for data from DVD to AVR, one for control/encryption of the link from AVR to DVD).
Now... to crossover the DSD it might not be at all a trivial task.
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