Mr White's "Opus", designing a simple balanced DAC

[JesseG]

Hi Guys

Sorry for crashing what is obviously a well-informed conversation with a newbie question. I'm hoping to learn something about these CD spinners.

The question is: how the heck does one identify the signals coming from the transport? I have been a computer tech for almost 30 years, so am familliar with the bits-n-bytes universe, but when I look at a candidate CDP I am stumped over the meansd to identify the traces on the ribbon running to the transport.

My current project is an old Pioneer PD-X303. This has two major plusses as a donor - 1) it looks like a very simple device and 2) I can live without it if I somehow destroy it

I have looked on the web for a schematic with no success (no big surprise). I think I just need a starting point. The silkscreen on the board has a number of identifiers, but I cannot make head ort tail from them.

Any hints or suggestions woul be a great help.


Jess

[ezkcdude]

Well, can you find the D/A chip? If so, look up the data sheet and identify the pins. Maybe that will help you.

[hifimaker]

Originally posted by ezkcdude



You have a design in the works over at headfi, right? That one uses CS8416, but it's in software mode and uses a PIC controller. I'm working on a design using the same chip, but in HW mode. I'm not sophisticated enough to use a microcontroller. Anyway, I've attached a preliminary schematic, which also includes AD1896 for re-clocking and PCM1794 for the DAC. I need to work on schematics for the power supply, clock, I/V and reset switch.

I think the TI/BB1792 and 1794 is a better chip.

-David

[ezkcdude]

Agreed. I think he's using the Wolfson DAC mainly because of the voltage output.

[pinkmouse]

Russ, I'm with you. The Wolfson DACs are extremely musical, and if the version you're using uses the Ringdac technology, even better. The Arcam Alpha 9 is the best CD player I have ever heard without spending totally silly money.

[hifimaker]

If the Wolfson chip is as good as Pinkmouse says it is, that would be great. They are less than 1/3 the price of the TI chip.

Wolfson does recommend an analog filter after the DAC, I wonder what Arcam uses?

-David

[Russ White]

Originally posted by pinkmouse
Russ, I'm with you.

HI Al,

I read through the datasheets of all the Wolfson DACs and just thought the WM8740 was the best match for my design goals. Differential output was a critical factor, and voltage output was a big plus. You also just can't argue with the specs and the number of very high end products which utilize the chip. You should be able to build a very good DAC with the chip with a minimum of auxilary "stuff" hanging off the PCB.

This is my first DAC design, it is not intended to be the "best ever" just "really damn good".

To all, Still looking for input on my reset scheme. Does it look reasonable?

Cheers!
Russ

[metalman]

Russ,

I completely agree with your Wolfson DAC choice. There are many pitfalls awaiting for a first foray into the digital world, and keeping your design simple will save a great deal of time in the development by limiting the permutations of troubleshooting that may be encountered. The Wolfson DAC is highly regarded and gives up little if any in performance when compared to other "Top of the Line" DAC chips, and as you have said greatly simplifies potential issues that need to be addressed.

Great idea, and one in which I'll heartily participate.

Terry

[metalman]

Originally posted by Russ White
Ok Will will do some searching, but even just one link woud be nice.

Russ, a good place to have a look is the HagDAC for a start.

[Russ White]

Terry,

Thanks for the input. It really helps to know that I am not in this alone. I am sure there will be a lot to learn along the road.

The K.I.S.S rule is certainly in full effect for me here. Having guys like you around helps keep me motivated. BTW I nearly have a couple of SuSy Channels ready to be fed from my XBOSOZ which I hope will soon be fed by this DAC.

Cheers!
Russ