Internal DAC upgrade in DVD player?

[Redshift187]

I recently fried the DAC chip in my DVD player when attempting to upgrade the analogue voltage regulator. The DAC analogue V+ and a voltage regulator for the muting transistors were the only parts supplied by the 11.5V instead of 5V they were supposed to see (backwards VR, oops!).

Something I had been considering, but I can't seem to find the information, is whether I can add a DAC board to the player and take the outputs from the decoder chip directly, rather than use an SPDIF->I2S and then DAC.

Details:
- this is for the front stereo pair only
- the decoder appears to output PCM
- the decoder is connected directly to the DAC
- the decoder has connections to the DAC software interface
- decoder IC is STI5519AVB
- DAC is PCM1742KE

Questions:
1. Can I tap into the digital audio lines and run those to an off-board DAC?
2. Do I need to worry about data format differences between CD and DVD?

[SoNic_real_one]

Just replace the DAC. It is software controlled so it will be a lot of work to replace it with anything else.

[Redshift187]

Since I don't like that answer and I have a few microcontrollers lying around, I'm going to hook one up to the micro input to the DAC and see exactly what settings are being used with different media. If I succeed, I'll post the results here.

[Leolabs]

The whole issue is about the decoder IC,what ever media goes through it,it'll do all the decoding and processing jobs(as long as long the format is compatible),and the outputs,usually the normal 3 wires interface(but not I2S) to the DAC,don't care what kind of media format.

Don't need to fuss around what kind of settings are they using unless you able to study the architecture of the decoding IC(and software too).

[Redshift187]

Well I'm interested in learning how all this fits together. The DAC in this player supports PCM data in standard, I2S and left-justified, 16 - 24 bits. I see no reason why I can't just connect an "external" DAC to the audio data lines, as long as I know what the data format is. Since the DAC is software controlled, I would think (but not assume) the data format will change between 16-bit and 24-bit depending on the media, which means I would need to control the "external" DAC with my own software, but that's not a problem.

I'm also very interested in the other settings the decoder sets, like de-emphasis, filter slopes, etc.

* "external" DAC in quotes because it will be inside the player on a separate board.

[Leolabs]

Yes,the DAC got all those functions you mentioned,BUT if you still required the DVDP function,then you have to implement your software design on the decoder section,which does have a separate flash MCU.

[Redshift187]

Not necessarily. I could intercept the format commands from the decoder and change them to the format required for the DAC I choose (since I notice every DAC seems to have a different interface for settings). That would probably be the only way to do it, since it seems the software for the decoder MCU is proprietary and not available.

[SoNic_real_one]

That is the only way to do it, but involves some/a lot of work in "translating" those few commands from the "old" DAC to the "new" DAC language.
This is because in the software controlled DAC's the control is done by programming different word codes in internal registers. Loading those codes might need different algorithm and then the data itself (that goes in the registers) need to be changed.

Take the datasheets for the two DAC's and you can do a comparison.

[Leolabs]

The main point is to study the output format of the decoder chip,which I believe still the old 3 wire(possibly left justified)format,which you can direct connect to a new DAC chip,try direct hardware connections to see will it works or not,rather than fussing around with MCUs.

[Redshift187]

Yeah, I have no problem with the software, I have more than 10 years experience as an embedded software developer

And I'm trying to figure out if this is possible before I spend money on a DAC, because if this is possible, I'll buy a cheap DAC without a receiver, like the Opus. If it's not possible, I'll save my money for a full, probably USB, DAC.