Retro fitting a USB DAC into a pre-amp - diyAudio
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Old 8th July 2012, 05:07 PM   #1
Autotat is offline Autotat  United Kingdom
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Default Retro fitting a USB DAC into a pre-amp

Hello, first of all I'd bette explain that I am a complete novice to this type of thing.

I have a Cambridge Audio C500/P500 Pre/Power Amp combination that has served me well over the past decade. However, my music collection is now stored on hard drive (lossless format) and accessed via a purpose built (well, assembled anyway) media centre PC.

I wish to put together and install a usb DAC into the C500 pre-amp to allow a direct source feed from the PC. It would tap into one of the now redundant original line level inputs

I have seen numerous circuit board DACs advertised on eBay for not a lot that would appear to do the job and am looking to see if I can integrate something similar into my amp, though perhaps using better quality components as necessary.

Does this sound viable? As I said, I am a novice and don't yet even know what the circuitry may require.

Below are some photos of the inside of the C500 to show what there is to play with. I have so far failed to find any schematics, though I have just contacted the manufacturer but I'm not holding my breath!

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I look forward to any replies. All help and guidance will be much appreciated.

Cheers.
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Old 8th July 2012, 09:28 PM   #2
Autotat is offline Autotat  United Kingdom
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I have found the following item on the Bay:

DAC-WOW USB POWERED HIGH PERFORMANCE DAC FOR YOUR PC | eBay

A lot of the cheap options don't appear to have there own power supply, relying instead on the power supply from the USB. Is this ok or are these types all a bit micky-mouse?

I'm a little concerned that it'll either struggle to do the job satisfactorily or that I'll start getting noise interference from the computer supplied power through the usb.

Cheers.
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Old 8th July 2012, 10:24 PM   #3
Pano is online now Pano  United States
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Hard to say about that eBay DAC, but why pay someone to do what you can do yourself?
There are plenty of cheaper DACs on eBay that use good chipsets and don't cost a lot. You might redo the analog output section, if you want. A power supply isn't hard or expensive. After all, this is DIY!
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Old 9th July 2012, 05:44 AM   #4
Autotat is offline Autotat  United Kingdom
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Thanks for the reply.

I would rather not buy one, I want to make one myself. I just need some guidance as to what I actually need to make.

Is this USB powered type of DAC a worthwhile consideration or should I opt for a powered build? I was hoping to plumb it into the amps existing power source.

I suppose a simpler question would be, can anyone recommend an existing USB DAC design that I can build myself and recommend which components I should use with a budget of up to 100?

I would still like to build it into the existing pre-amp though to keep the number of boxes to a minimum. My wife uses the stereo and is going to get put off by the 'silly great big thing' if there is yet another box cluttering up the place that she has to switch on.

Many thanks.
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Old 9th July 2012, 06:52 AM   #5
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So how are you currently feeding the amp? 3.5mm splitter on analogue?

Not sure as to the wisdom of avoiding another box, and you will have many more unexpected issues and complications in incorporating it in the amp.... And what happens when/if the amp goes phut or you upgrade?

My mains powered commercial DAC has run continuously apart from moving house, or power cuts, for the last 4 years, feeding both analogue and spdif to the amp. At about half the size of my external backup drives, it is almost unnoticeable.

There are several DIY projects here, DAC 2496 (AK4393) DAC KIT With CS8416+AK4393+5532 being particlarly well documented, with several variations on spdif/usb inputs.
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Old 9th July 2012, 07:31 AM   #6
orpheus is offline orpheus  United States
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Get an ODAC. Google NwAvGuy, and look on this forum. Usually for sale around $100, and it is a great sounding converter, with extensive published excellent measurements. I'm listening to one now, and it sounds really good. USB bus powered, small, and would be very easy to install into the preamp you have pictured.

-Aaron.
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Old 9th July 2012, 08:44 AM   #7
qusp is offline qusp  Australia
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the ODAC is good value and good performance, but hardly DIY
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Old 9th July 2012, 12:01 PM   #8
Autotat is offline Autotat  United Kingdom
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Thanks for the replies.

At the moment, bearing in mind that the media centre PC has only been operating for about a month, the sound signal has an ardous route. It leaves the PC via HDMI to the TV. Then, from the TV via SPDF to a Yamaha E800 AV processor. This converts what's left of the signal to analogue and send it through a decent pair of leads to the C500 pre-amp.

Thanks for the link to that DAC kit, it does sound promising.

What kind of trouble am I inviting by sharing the pre-amps power supply? It has the ability to power an optional phono stage so I didn't think there'd be much of a drain on its resources powering a DAC. Or are you refering to other potential problems such as induced noise?
I have no intention of replacing the amp for a while yet and am quite looking forward to seeing what I can do to maintain its usefullness as I rather like it.

I googled NwAvGuy and selected the link to this forum as instructed. He seemed to state that the DAC was dissapointing. Or has it been developed since then? I'll have another look when I have more time (supposed to be working).

I'm really quite enthusiastic about the prospect of this now, dispite not nowing my ar*e from my elbow.

Thanks for the help.

Simon.
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Old 9th July 2012, 05:59 PM   #9
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Hi Simon, I suspect the biggest danger is nothing to do with the available power but what quality the supply is and any interactions with a built in DAC from what is swimming around in the amp casing or vice versa effect. ie - Why create the potential problem to resolve if you can avert it?

Your existing long route via TV relies on conversion to SPDIF at the TV, and subsequent conversion at the Yamaha to analogue onward to the preamp. The new DAC may or may not be better on audio, but will you not need the Yamaha anyway for DTS decodong etc?
Have you tried the SPDIF out from the computer to the Yamaha for comparison?

eg - The conversion to optical on my desktop is inferior to the usbDAC hence coaxial onto the AV receiver with it's built in DACs (coax sounded better than optical on the receiver). For simplicity of use the USB Dac covers album audio from the desktop, and reverts to optical out from the motherboard for film.

Were I to build a better DAC, it would hopefully pass forward DTS etc, but the above may no longer prove true. I have the capability to swap the bits to find the best options, something your intended path would not permit.
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Old 9th July 2012, 07:48 PM   #10
Autotat is offline Autotat  United Kingdom
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Well the supply must be a good one, it says so itself on the label!

I can see what you are getting at. I guess the best way would be to give it a go and if it does prove to be a bad idea I'll remove it again and put it in its own box. At least then I've try'd and learnt from it.

The DTS signal path is alright for watching movies, the sound is acceptable for that. It also means that the signal from the cable TV box passes through the same input so the wife doesn't need to change the input selection on the AV amp. Anything to keep things simple for her to use.

I try'd the direct connection from PC to AV Processor but got no sound and haven't try'd since, I really must look into that.

I'm only interested in improving the stereo signal at present as I much prefer to chillout immersing myself in music with the lights turned down. (that makes me sound like a right nonce! )

It appears that you have a similar set-up to that which I am aiming for (apart from the film signal traveling via the TV).

Cheers for the help.
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