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Old 1st September 2010, 07:26 AM   #1
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Default PC based audio to amplifier via DAC - confused?

Hi all

I am planning my audio adventure and want to get things clear in my head. I plan to initially run a chip amp (one of Peters) and connect a CD player (Denon DCD 1500II) and my PC to it, the PC having Flac, MP3 and AIFF copies of CD etcs. I understand from reading threads that I need a DAC to improve things (back to analog) but this is where I get confused.

All the DAC's I have seen have BNC connectors or USB connectors yet, to date, I haven't seen a sound card with either. I would probably be using a Sound Blaster Audigy 2 card in the PC but getting the output from there to a DAC has me baffled.

Does anyone care to enlighten me on the RIGHT way of doing things - connecting my PC to a Gainclone/Chip amp...

So confused.....

Cheers
Bruce
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Old 1st September 2010, 07:36 AM   #2
sangram is offline sangram  India
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DACs come with Coaxial (RCA connector or BNC, most commercial models use the RCA), USB and/or optical SPDIF inputs. The number and type of inputs vary across DACs, but most come with at least 2.

If you use the USB connector to hook up your PC it connects to the USB port of the computer. A soundcard is not needed, it is built into the DAC - however the plug and play versions are restricted to 48KHz samplerate. If you use coax you have to connect the Audigy's digital output to the coax input, a special cable is needed to convert the miniplug output available on the card (if it is a miniplug and not RCA).

If your DAC already has only a BNC input, you can use a BNC-RCA converter to hook up a coax output such as that on your CD player or soundcard.

If you're not using a DAC you can go direct from soundcard output to the input of the gainclone.
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Old 1st September 2010, 07:53 AM   #3
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Aha, a light is coming on in my head

I haven't got a DAC yet, I was considering one of Peter's DAC, hence the reference to BNC & USB.

Bit of background. I currently have a Pentium 4 3.2Ghz machine as my media server. It runs MythTV for TV and XBMC for everything else (TV series, movies & music). It is connected to a no name AV 5.1 amp for the video side of things but music only sounds average.

So I want to introduce a chip amp specifically for music and take the output from this PC (or another specific one for music) and output it via the amp. The second (planned) input to the chip amp will be connected to the RCA output from the cd player.

I (looks like mistakenly) always thought I needed a DAC to do that to get the best sound as the output from the PC was digital and had to be converted back to analog somewhere along the line.

However, I did not know that audio can be output from the PC USB port (if that is what you are saying?) so I will have to look into how that is done.

Cheers
Bruce
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Old 1st September 2010, 08:09 AM   #4
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Ok, think I got it....

Plug the DAC into the PC via USB cable then set ALSA to use the USB port as the output. As DAC does the processing, no "external" sound card needed.

Please do correct me if I am wrong.

Cheers
Bruce
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Old 1st September 2010, 08:29 AM   #5
sangram is offline sangram  India
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Peter will put an RCA connector there if you request him, I'm sure. Else you can get a custom cable made with a BNC at one end, the format is exactly the same though a BNC is much more reliable connector, as well as perfect 75ohm impedance, not many RCAs can claim that - if any. I'm not sure the DAC can be switched between SPDIF and USB though, you'll have to ask Peter about that.

Another possible customisation is to use two separate SPDIF inputs with a small switch, that way you can also try out the DAC with the digital output of your CD player. I know that that DAC is very good (have heard it personally) and can compete with many high-dollar CD players. It's definitely worth a shot, and a switch means you won't have to constantly unplug cables

The most common solution for these kind of USB implementations is to use a TI PCM27xx chip (a 'USB DAC', if you will) with an I2S or SPDIF output and interface it to a DAC chip. The 48 KHz restriction remains as it is inherent to the interface, the same is not applicable to the SPDIF input. Here is an example of such a beast: http://twistedpearaudio.com/digital/usb.aspx

For the best results you should get a BNC input and a custom cable. Someone I know went from an Audigy to a much better card to handle the digital output duties, but perceived no change so I would guess the Creative is good enough.

You got the USB thing down perfectly. That's exactly how it works, though I'm a Linux ignoramus.

How is you PC connected to the receiver - Analog outputs, or digital?
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Old 1st September 2010, 11:53 AM   #6
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Thanks again sangram for the info, very helpful. It sounds like the best way to go (for a standalone DAC) would be BNC which I will look into. If I could get away with using the the default sound system on the motherboard I will, otherwise I'll look at the Audigy

My ultimate goal is to integrate Peter's DAC and amp together so that the 2 sources I would use could both use the DAC side. When switching, say, from Media Centre to CD the input would still go via the DAC internally. I suspect this is a little different from what others have done so it could be an adventure, I don't even know if it would be possible with Peter's DAC!

Currently from our media PC to the AV unit I am using a TOS link directly from the motherboard. The AV unit however isn't too good at it so a better one (name brand!) may be in our future.

Cheers
Bruce
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Old 1st September 2010, 03:47 PM   #7
sangram is offline sangram  India
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You could make it work with a MUX (digital input selector, one such is available at the Twisted Pear site), and Peter's DAC, you'll have to tap into the I2S line of the TDA1543 which is not a problem

Good Luck!!
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Old 10th September 2010, 02:17 AM   #8
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Just a question. Why use the Dennon at all. I assume your computer has a DVD drive.

Terry
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