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Old 13th February 2014, 05:54 PM   #1
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Default Diy DAC for home theatre.

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,

EDIT: Any links to other posts with people talking about this would also be great!!!!

Last edited by FranciscoPerez; 13th February 2014 at 06:01 PM.
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Old 13th February 2014, 08:04 PM   #2
Bigun is offline Bigun  Canada
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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!
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Old 14th February 2014, 08:10 AM   #3
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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!

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Old 14th February 2014, 09:41 AM   #4
Julf is offline Julf  Europe
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Originally Posted by FranciscoPerez View Post
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.
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Old 14th February 2014, 10:09 AM   #5
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Thanks Julf.
I'd better go and buy one of these boxes then.
One thing I noticed is that receivers come with the amplifier included. Do you know some brands or specific comercial devices which just decode the hdmi audio signal into 8 analog channels without amplification? I'd like to use my own diy 8 channel amplifier if possible.

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Old 14th February 2014, 10:25 AM   #6
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Search for an Audio/Video or Home Theater preamp, if you don't want the amp part. But they're usually more expensive than integrated av amp.
Emotiva has some of that "not that expensive" type of preamp :

Last edited by moumousganou; 14th February 2014 at 10:28 AM.
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Old 14th February 2014, 10:47 AM   #7
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Great moumousganou!
You were right! There's no way I'm gonna diy something like this!

Click the image to open in full size.

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!

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Old 14th February 2014, 11:56 AM   #8
sesebe is offline sesebe  Romania
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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".
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Old 14th February 2014, 12:12 PM   #9
laplace is offline laplace  Australia
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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.
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Old 14th February 2014, 12:41 PM   #10
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Would the Oppo 103 or 105 work as a Pre-processor followed up with DSP and amps? Limitations?
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