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Old 29th July 2003, 04:28 PM   #11
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Hey, next weekend if far sooner than need be, take your time. I believe we just recently got silkscreening capabilities. I know we have the ability, I'm just not sure what is available to students. I'll get back to you.
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Old 2nd August 2003, 08:29 PM   #12
DJ is offline DJ  South Africa
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Hey dunderchief

I've just started looking over the info I have on various ICs etc for the DAC project. Since Texas Instruments make some of the best ICs for our purposes, and they have a very nice sample programme, I'm going to try to use mostly their products. So far, this is the basic ideas I've come up with:

8 separate DAC channels

1x balanced & 1x unbalanced output per channel

super low jitter clock circuit

totally separated digital and analogue power supplies (perhaps more than one of each)

high quality low pass filter to ensure maximum amount of noise from digital circuitry is removed

Most of this would seem obvious, but I'm just stating it so you know I was busy with the project over here. I will start drawing up the schematic next weekend, if not tomorrow.

Cheers

DJ
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Old 2nd August 2003, 10:35 PM   #13
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Sounds like an plan to me. Any idea specifically which TI chip you like? Power supply is where I'm most interested in design. While I'll certainly be making one of these for home use I'm also considering using in a mobile situation, doing active crossovers through a computer in my car. I'm gonna start designing a PS that will run off of 12v DC, but that's another story, it will certainly be going in the home first. Am I correct in saying that you're in South Africa? If not where are you? I think my program has a pretty good deal with both TI and Nation as far as getting parts so if you were interested I could be getting twice the parts needed and be able to send them to you. Keep me posted

Cheers
-Steve
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Old 8th August 2003, 06:58 AM   #14
DJ is offline DJ  South Africa
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Hey again...

Well the chip I would most like to use is TI's PCM1792, because it's their best performance DAC. Sadly it's not on sample, so I think I'll go with PCM1738 which is almost as good. That is unless you can get us some 1792s.

Also from TI, I would like to use the PLL1708 as part of the clock circuitry. I intend to spend a lot of time finetuning the clock, since this can obviously have great effects on the final audio quality.

I'm still not sure exactly what opamps I will use, but it will probably be OPA627 or 637 (singles) and OPA2132 or 2134 (duals).

Like I said I'll hopefully get to drawing up a basic schematic this weekend. Oh, and yes I'm in South Africa.

Cheers for now.

DJ
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Old 10th August 2003, 06:05 AM   #15
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OK, so I've been looking over a bunch of stuff and I'm wondering what the input section of the DAC is going to look like. Will it simply take a 2ch input and break it up into 4 left and 4 right analog channels, or will it accept 8 different channels. I'm still reading up on the limitations of the SPDIF system.
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Old 10th August 2003, 01:14 PM   #16
MWP is offline MWP  Australia
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Quote:
Will it simply take a 2ch input and break it up into 4 left and 4 right analog channels
Sure, split the SPDIF into I2S, then feed it to your 4 DAC ICs.
Itll only be stereo tho... you cant do anymore than 2 channels using plain SPDIF.
To go over 2 channels you need to do Dolby AC3, DTS, etc. which cant(*) be done DIY.

* - ok, it can, and has been, but if your asking about this stuff you wont be able to do it... i know i cant.
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Old 11th August 2003, 08:51 AM   #17
DJ is offline DJ  South Africa
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Hey again Steve.

Sorry but I didn't get very far with the schematic over the weekend since I was ill. My head is still spinning a little.

Like I said previously, I would like to make 8 totally separate DAC channels. Implying that you can configure them in many ways, ie one stereo input out to all 8 outputs or 8 inputs out to 8 outputs.

True you don't get home cinema processors that puts out all the separate channels digitally, but that is one of my (very ambitious) projects for later on. I need to build such a processor since I am planning to build my active TDAA powered speakers next. No DAC and digital all the way to the driver. Ask if you wanna know more.

What have you found out about your PCB facilities?

I'll keep you updated and I'll probably have hte schematic done at the end of the week.

DJ
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Old 11th August 2003, 04:51 PM   #18
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I'd be really interested in the TDAA design, but I have to say I know little to nothing about the concept.

How do you plan to receive 8 digital channels to the DAC? Since standard SPDIF can only send 2ch will you have 4 inputs? Just trying to get a full grasp of what's going on.

Being as it's summer term the person I wrote to at University is a little slow in getting back to me. I'll let you know as soon as I hear from them on the what we can do about PCB's.

Thanks again.

Cheers
-Steve
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Old 12th August 2003, 08:42 AM   #19
DJ is offline DJ  South Africa
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Yes and no. Each channel will have it's own input, but you will also be able to route one or two inputs to all the other channels. So the idea is to make a really flexible DAC. 0 - 8 inputs out to 8 outputs. Get it?

DJ
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Old 12th August 2003, 11:46 AM   #20
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Not unlike an 8in 8out router. Will it have glitchless switching ?

ray.
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