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Multiple SPDIF inputs to DIY DAC (help for DIY novice)

glancaster

glancaster

In the silicon vale
Dear All

Hoping to tap into the wisdom of the pink fish DIYers...

I've tried many commercial DACs over the past few years in an effort to match the sound quality of my Avondale-modified Arcam Alpha 5+ CD player (AAA5+) and better that of my 'stop-gap' Moodlab DICE DAC. I've listened to lots up to about the £800 mark, but not managed to find anything that suits. Both my existing units are non-oversampling, multibit DAC chips (TDA154*) and have excellent timing (basically – they rock!), if not the last word in detail, which may give an idea of the sound I like.

I have an idea now to build my own DAC. My DIY skills are modest – I can wield a soldering iron, and have made up cables, replaced output sockets, and the odd component here and there, but I'm not confident enough to build a whole DAC from scratch myself. Certainly not a power supply where mains voltages are involved. Therefore I was looking at ready assembled boards that I could just put in a case and wire up.

I noticed the DDDAC 1794 NOS project:

http://www.dddac.com

They do whole boards ready assembled, including the power supply boards. The NOS nature of it, and good reviews, suggest it might suit me.

One snag – I really need both coaxial and toslink inputs. It seems that the ready made boards support only USB and coaxial, as explained here:

http://www.dddac.com/dddac1794_spdif.html

Is there a simple way to modify this design to support both coaxial and toslink inputs?

Or is there a simple, inexpensive, ready-made box that can do the switching without sacrificing sound quality?

Or should I have a more fundamental rethink?

Any help appreciated.

Kind regards

- Garry
 
To do the switching you need one of these from twisted pear.

http://twistedpearaudio.com/digital/cs8416mux.aspx

if you need optical inputs as well you'll need some TOSLINK modules also from twisted pear.

http://twistedpearaudio.com/digital/torx.aspx

In fact, I'd seriously consider the Buffalo DAC from twisted pear also, it's a darned fine DAC and he modularity of the switching makes it all very easy to add the extra cards needed for multiple SPDIF sources or a PCM/DSD source as well. They have good support in the DIY community forums as well as their own forum, many of us on here have built a buffalo DAC over the last couple of years and couldn't be happier with them.

http://twistedpearaudio.com/digital/buffalo8.aspx
 
Dear orangeart

Thanks for your reply.

I did consider the Buffalo DAC. (I was slightly tempted by the assembled boards you have for sale in the classifieds!)

The main things that put me off were:

1. The Buffalo power supplies don't seem to be available in pre-built form. As I mentioned above, I'm really not confident enough to build these, although I suppose any pre-built module from elsewhere would work provided it has the same voltage, sufficient current, and was otherwise of adequate quality. Would that Buffalo 'S/PDIF 4:1 MUX/RECEIVER MODULE' even work with the standard DDDAC supply – if so that might be a way forward?

2. I've heard a DAC before that used – I think – exactly the same Sabre DAC chip, the Young DAC. Whilst there were some things I liked about it (plenty of that 'inky blackness' stuff), I found that, in my system at least, it had an over-emphasis on the treble. Perhaps more worryingly, there was a distortion problem on the loudest parts of certain tracks – those that had been mastered 'hot'. It seemed that some part of the Young (or this particular Young, at least) had insufficient headroom to cope with the very loudest signals. Not a problem I've experienced on any other DAC I've tried including, to be fair, a DAC using a different member of the Sabre family. Still, it's left me a bit wary of that particular chip.

Kind regards

- Garry
 
Thanks Paul – that does seem like a simpler option, that would still fulfil my requirements.

Whilst that switching module is only available as a kit, it's a pretty simple one, and no mains voltages involved. I think I might be able to manage that.

I'm thinking that if I bought that kit, plus:

1 x Twisted Pear '4-Input Selection Switch Kit'
2 x Twisted Pear Toslink modules (http://twistedpearaudio.com/digital/torx.aspx)
2 x coaxial sockets

I would get 2 x coaxial and 2 x toslink inputs and could run that all off the existing DDDAC 5V supply (also used to power the DDDAC 'WaveIO' USB receiver module, but not the motherboard or DAC boards).

This is probably a stupid question, but is it just a question of connecting additional wires from the 5V power supply outputs to the power supply inputs of these boards? Or is there more to it that that?

Kind regards

- Garry
 
Essentially. But you may want to consider galvanic isolation between the sections. It may be better to let the USB source supply the WaveIO, then use its isolated outputs to the DDDAC and supply the S/PDIF mux and TOSLink receivers from your local 5v. That way the earth from the PC can be separated from the signal 0v in your DAC.

If you want to supply the WaveIO locally then you need a separate transformer winding and a 5v regulator. But if you use this to supply the mux you will be joining the 0v together and defeating the object.

It's not as complicated as it sounds, the entities are just multiplying rather too fruitfully.

Paul
 
Hi Paul

Thanks again. I understand some of your explanation, but I am confused about the grounding issues :confused:

The DDDAC designer says that the WaveIO module performs better running off a power supply not USB power, so that's really what I'd want to do.

There's a lot of talk of 'isolation' on the DDDAC WaveIO web page:

http://www.dddac.com/dddac1794_usb.html

I took this to mean that, as long as we run the WaveIO off a power supply (not off USB power) we are isolated from the USB connections, including 0V?

Hmm, this seems to be a more complex issue than I'd hoped...

Kind regards

- Garry
 
Hi Garry,

The DDDAC's chipset (BB 1794) is the same type as used in the Young Dac (BB 1795) that you did not like, so you might want to listen to the DDDAC first. I had the same experience with the BB/TI 179* chipsets sound, that of hard/harsh high frequencies which a well sorted Sabre 9018 doesn't have. My humble experience/opinion though :).

Kind regards
Cornelius
 
vanwykca said:
Hi Garry,

The DDDAC's chipset (BB 1794) is the same type as used in the Young Dac (BB 1795) that you did not like, so you might want to listen to the DDDAC first. I had the same experience with the BB/TI 179* chipsets sound, that of hard/harsh high frequencies which a well sorted Sabre 9018 doesn't have. My humble experience/opinion though :).

Kind regards
Cornelius
Click to expand...

Hi Cornelius

That's a very good point. All this time, I was thinking that the Young used a Sabre chip but, having Googled it, you are right - it doesn't!

Time for a rethink!

Kind regards

- Garry
 
glancaster said:
Hi Paul

Thanks again. I understand some of your explanation, but I am confused about the grounding issues :confused:

The DDDAC designer says that the WaveIO module performs better running off a power supply not USB power, so that's really what I'd want to do.

There's a lot of talk of 'isolation' on the DDDAC WaveIO web page:

http://www.dddac.com/dddac1794_usb.html

I took this to mean that, as long as we run the WaveIO off a power supply (not off USB power) we are isolated from the USB connections, including 0V?

Hmm, this seems to be a more complex issue than I'd hoped...

Kind regards

- Garry
Click to expand...
The WaveIO is always connected to the computer, whether it is taking power or not. It has isolated I2S outputs which allow the connection between the ground of the WaveIO/PC and the rest of the DAC to be broken. But for this to work the power supply to the WaveIO also has to be isolated from the rest of the DAC. Essentially this just requires a separate mains transformer winding.

An initial setup using PC power would keep things simple.

I've no view on the BB DAC, I use a Twisted Pear Buffalo and feel no inclination to change, and I didn't even get around to coupling the WaveIO I2S up to it, so far I've stuck with the S/PDIF. Now using a Raspberry Pi, also with an S/PDIF output. A new year project to sort out I2S for the main source.

Paul
 
Paul R said:
The WaveIO is always connected to the computer, whether it is taking power or not. It has isolated I2S outputs which allow the connection between the ground of the WaveIO/PC and the rest of the DAC to be broken. But for this to work the power supply to the WaveIO also has to be isolated from the rest of the DAC. Essentially this just requires a separate mains transformer winding.

An initial setup using PC power would keep things simple.
Click to expand...

Thanks for explaining that - now I understand.

Paul R said:
I've no view on the BB DAC, I use a Twisted Pear Buffalo and feel no inclination to change, and I didn't even get around to coupling the WaveIO I2S up to it, so far I've stuck with the S/PDIF. Now using a Raspberry Pi, also with an S/PDIF output. A new year project to sort out I2S for the main source.

Paul
Click to expand...

Best of luck with that Paul!

Kind regards

- Garry
 
Hi Garry - what did you go for in the end? Did you get the DDDac? I'm looking at a similar DIY project and would be interested in your feedback
 
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