Diy DAC for home theatre.

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Hi everybody! First post on this subforum. :)
First of all I'd like to apologise as this post may sound too vague or already answered before. I tried the search function but I'm kinda lost in all the info found over here.

A friend, knowing that I usually build amps and speakers, recently asked me to build a 5.1 or 7.1 home theatre system for his new Philips TV. He wants to watch TV (when multichannel is supported), Dvd movies or play video games taking advantage of more than just two speakers.

I'd like to build a DAC in order to decode the Optical audio output of TV, DVD, or game console into all possible different analog channels supported.

I'm a complete newbie regarding DACs, digital audio formats, etc and as you see I'm kinda lost!! Please, could someone give me some schematics,tips, or guidance on this?
First of all,maybe I'd need to know the audio format that the TV, DVD player etc outputs prior to building the appropriate DAC, is that right? Isn't there a standard industry audio format used for most applications?

Thank you!!!
Kind Regards,
Fran

EDIT: Any links to other posts with people talking about this would also be great!!!!
 
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I don't know much about it either but I suspect that what you are thinking of doing is a huge and complex project. For todays multi-channel home theatre and multi-source systems I have already decided that it's really better to go out and buy something commercial - such as a home theatre receiver or one of the Oppo players. Just my 2c from a position of mostly ignorance!
 
Thanks Bigun!
I'm sorry to hear that :( Let's see if someone corroborates that.

I had a look at comercial home theatre receivers, but they seem to be quite expensive! At least not less than 250 quid. The Oppo players look nice, but they're quite pricey (not saying they're not worth it) and I'd like to cut costs as much as possible. It's surprising for me, given my complete ignorance on this subject, that a device that splits the digital audio into different analog channels costs so much!! I thought with just a chip and some components I'd be good to go!

Cheers,
Fran
 
Isn't there a standard industry audio format used for most applications?

Let's start with the actual connection - the current standard is HDMI. That is just the start.

What you want to do is not just a simple chip or two. It is a pretty complex thing. No way you will be able to do it without a fair bit of specialist knowledge - and no way you could do it cheaper than a mass-produced box.
 
Great moumousganou!
You were right! There's no way I'm gonna diy something like this! :D

umc200_top2_1024x1024.jpg


The UMC-200 seems exactly what I need, but I think it's out of my friend's budget. Maybe some cheaper integrated av amps also carry preamp outputs, and are something cheaper. I'll have a look!

Thanks!!!!
Fran
 
Hi,

If you ask about only 2 channels (stereo), is not a problem. Can be done freom simple to complex.
For 5+1 (6 channels) you need to decode first the data from the incoming format (there are more then 1 format) and after this you will have 3 sets of digital data lines that can be converted to audio with your favorite DAC cips.
The problem is with the decoding because this can not be done pure hardware (I do not know a chip that can do this alone without software). If you find this chip, than it is "easy".
 
A DAC is relatively easy (DAC chip plus opamp plus a little passive filtering+support circuitry), but you seem to be talking about a surround decoder, which requires a bunch of licensed (with fees!) software to decode all the various formats such as AC3 and DTS into PCM (raw audio) that you can feed to a DAC. That means a big DSP, lots of custom software and paying for binary modules to do the specific decoding options. Unless you have significant prior experience with building DSP systems, I would not go near this project with a bargepole.

The cheapest option is to look for an external soundcard like an old Extigy which has SPDIF-in, will theoretically decode a couple of basic stream formats when running standalone (no PC connection), and has 5.1 analogue outputs. You can find those secondhand for <$100 but getting it all working is hard because their driver support is mostly for ancient versions of windows, and they don't support a lot of stream formats. There might be newer+better decoder modules that I'm not aware of though.

What I did is buy a Yamaha RX-V667 (about $350 from Amazon) which does all the current formats and has 7.2 pre-outs (from quite-good DACs) that I can use with active crossovers. It also has not-entirely-shabby amplifiers built-in that you can use straight out of the box if you're into building speakers more than amps.
 

rif

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Would an atlona hd570 meet your needs? I sold one recently, I think they're about $200 new. Here's the description:

The Atlona AT-HD570 is a professional quality HDMI Audio De-Embedder. Unit is capable of accepting an HDMI input signal and de-embedding the audio signal to either Optical or Multi-Channel analog audio outputs. This audio decoder supports uncompressed analog LPCM 7.1, 5.1, 2ch through the mulit-channel analog outputs with Dolby Digital, LPCM 2CH and DTS output through optical connection. Supports Dolby True HD and DTS HD Master Audio pass through HDMI connection.

De-embeds audio signal from HDMI source.
HDMI LPCM 7.1 decoder
HDMI input and HDMI output
Switch for bitsream, LPCM, 5.1/7.1, or 2ch
Optical output
Multi channel analog outputs: FL/FR, LFE/FC, RL/RR, RLC/RRC
 
Thank you!!!

Now that I have a general idea of what’s going on inside a surround decoder, I agree with all of you, I’m far from being able to build one of these. Even with the proper knowledge, it’d be too complex and expensive so it’s not worth it for building just a single unit. I also thought that common audio formats were open and free, and you could find already programmed daps which would do the job.

Thanks for the external sound card idea!! Anyway I think it would be better to go for something standalone, and as compact as possible.

The Oppo 103 seems like the best option!! Still a little expensive but looks kinda well built and with lots of features, so I'll encourage my friend to go for it.

About the atlona hd570, it could also be a good idea but I’m a little concerned about the quality of it. What's your personal opinion? The good thing is that I could get rid of its case and integrate the circuitry inside the amp to have both the processor and amp in the same box.

Your help is much appreciated!!
Cheers,
Fran
 
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