Building a DAC from Assembled DAC7 parallel dual WM8741 + WM8805 + CM6631A +AD627 PCB

[whinge]

Hello Forum!

I would like to build a DAC from the following pre-assembled board (eBay member happyshop 1982)

Assembled DAC7 parallel dual WM8741 + WM8805 + CM6631A +AD627 board | eBay

or - different seller (eBay member min9988)

Assembled DAC7 parallel dual WM8741 + WM8805 + CM6631A +AD627 board | eBay

I used to make some of my own boards 30 years ago, so, am very rusty! I have soldering equipment now and am using this project as a way back into electronics: a hobby - to learn and enjoy. Ultimately I would like to build my own pre/power amp also - but want (for many reasons) to start with this DAC project.

I currently have a Musical Fidelity V90 DAC which "blew my mind" when I heard the difference from a 'standard' source: I am hoping that this board will out-shine the V90 and produce an even more thrilling sound.........

I only want an optical input for this project so am not worried about a/the USB input (that will be my next project: producing a "good" optical out from a PC... but first things first!)

I have been told by eBay seller (happyshop1982) that the power supply requirements are "AC 16V 0 16V and 9v 0,9v 0" - another eBay member has suggested this transformer as suitable

30W R Core Transformer Primary?2X115V Secondary?2X16V 0 10V 0 10V | eBay however, this seems a bit "cheap"?

I would like to build my own suitable good quality separate power supply and was considering two or three torroidal transformers to suppy the "AC 16V 0 16V and 9v 0,9v 0" - please does anyone have any advice on suitable transformers/design ideas to best supply this board? Perhaps even updating/adding to the onboard capacitors etc...?

On the (analogue?) section it appears that the (opamps?) are easily replaceable - any suggestions here on improving sound quality?

Also, does anyone have a schematic for this board and any clearer pictures please?

Finally: a sincere thank you to everyone who replies. I am really trying to understand the board/processes and any possible modifications - I am not afraid to do a bit of soldering etc. - just nothing too 'precise' to start off with!

I am 'all ears' - thanks again everyone!

 

[kinsei]

these are nice boards to work with but just reminded:
the 7pin daughter board only do usb->spdif, not usb->i2s, that means you will need some extra effort to make it truely usb input by bypassing the onboard 8805

 

[whinge]

Hi kinsei,

I'm only looking to have an optical in for this project no USB (I want that as a separate unit / project) thanks.

Any advice about this board regarding building a power supply / replacement opamps etc please?

I know that I will be opening a can of worms by asking the following, so, I will post it as a separate thread: alternatives to this board for a good quality 'DIY' DAC.

Many thanks for replying.

 

[plasnu]

WM8740 / 8741 sounds great with passive output with 600 ohm transformer.

 

[whinge]

Hello plasnu,

I'm coming back into electronics after 30 years, so, please excuse my ignorance:

"8741 sounds great with passive output with 600 ohm transformer" - please could you explain how to implement that in practice?

Also: any simple advice on power supply please - I want to make it a separate unit - two/three torroidal tansformers? Any design ideas please?

Many thanks

 

[plasnu]

Hello plasnu,

I'm coming back into electronics after 30 years, so, please excuse my ignorance:

"8741 sounds great with passive output with 600 ohm transformer" - please could you explain how to implement that in practice?

Also: any simple advice on power supply please - I want to make it a separate unit - two/three torroidal tansformers? Any design ideas please?

Many thanks

Hi there,
I'm posting from ipad, so I can't attach the link, but there is a thread about 8741 with transformer output on this forum. I modified my DAC with transformer, and I prefer it to the stock opamp output. I have no advice for psu, sorry...

 

[whinge]

http://www.diyaudio.com/forums/digital-line-level/199283-wm8741-dual-differential-output-stage.html



Thank you!!! Now for some reading...

 

[whinge]

Hi plasnu

I read the thread, but, could not glean enough info from it to understand how to design/build what you mention.

Do you have any further info / search terms for me to research please?

Many thanks for your time.

 

[Spartacus]

My suggestion if you are feeling rusty, is to keep your goals simple and easily achievable at this stage. Build the thing as it is intended to be built, then branch out when you confidence and knowledge has grown.

Opamps can sound good, and you can usually better the ones installed with these kits. There are plenty of pages discussing which devices are best - I'm currently using two opa827s, which are very good.

Don't bother with an external supply, there is no need. Also R-cores are better than toroidals the these purposes as they pass less noise from the mains. So go with the one recommended.

All the best!

 

[whinge]

Thank you Spartacus - that is exactly the kind of post I was hoping for as now I know that I can start! (Learn, make mistakes, correct...)

Is there any real difference in quality of the following v1.1 board in your opinion:

Dual WM8741 24/192K input ultra DAC assembled new version thick copper PCB ! | eBay

So - can I just buy two opa827 and fit them to the board?

Fantastic news on the psu advice also - many thanks

 

[Spartacus]

I'd go with the cheaper board, then upgrade it myself. OPA827s only come in single SMD packages, so you will need to fit two of them onto an adapter. There are other good parts, such as ADA4627 and the ADA4898 which comes as a dual.

 

[whinge]

Thank you Spartacus

I think that I will follow your advice - I am learning a huge amount - I will go down the transformer route eventually but most probably try your latest opamps suggestion after getting it up and running then

Do you have experience with transformers in this scenario?

 

[whinge]

Please could someone describe the relation of i2s input with this board?

As a next project - I want to join a custom PC to my DAC using this board: Amanero usb iis 32bit 384K DSD512 Async USB to I2S USB card | eBay

How do you find out the relationship between i2s and what audio to feed into the board please?

 

[Spartacus]

Thank you Spartacus

I think that I will follow your advice - I am learning a huge amount - I will go down the transformer route eventually but most probably try your latest opamps suggestion after getting it up and running then

Do you have experience with transformers in this scenario?

Hey, sorry for the late reply I don't seem to be getting en email alerting me to replies. Anyway, about transformers - yes i did try a pair once. They were OK, but not great. However they were cheap, so I don't take this as a reflection of transformers' goodness or otherwise. I do have another pair of Lundahls I've been meaning to try, but not gotten around to.

Please don't interpret my suggestion to try op-amps first as a discouragement - experiment away by all means. It's really just a question of managing the complexity of the project. Plus, if you try one way first, then try another, you learn something in the process - the sort of learning no "guru's" advice can provide.

 

[whinge]

Hi Spartacus,

if you try one way first, then try another, you learn something in the process - the sort of learning no "guru's" advice can provide.

Great advice - many thanks indeed

 

[phase]

I have a board that is very similar from the same maker, has a single wm8741.
The transformer will benefit from having a snubber circuit added, and by having the transformer separated by a steel panel if in the same housing as the board.

The op amp circuits have added bias resistors and will likely do better with that situation reduced or eliminated completely.

Nearly all of the capacitors could be improved without spending a large amount on exotic parts. Be careful regarding heat transfer to the WM8741 if you replace the mid rail capacitor, found that out the hard way.

I used a bare wire jumped from the smallest electrolytic bypass to the power pins for the op amps, made a good improvement. The Burson V4 op amps have sounded the best so far.

The servo op amp sounded best with an op627, and 1uf k74 polystyrenes in place of the .47uf box caps, had to be mounted off the board.

Lots of potential I have discovered...


The output resistor can be replaced with a lower value, think I used 18r, Caddock.

 

[trumbe]

I have a board that is very similar from the same maker, has a single wm8741.
The transformer will benefit from having a snubber circuit added, and by having the transformer separated by a steel panel if in the same housing as the board.

The op amp circuits have added bias resistors and will likely do better with that situation reduced or eliminated completely.

Nearly all of the capacitors could be improved without spending a large amount on exotic parts. Be careful regarding heat transfer to the WM8741 if you replace the mid rail capacitor, found that out the hard way.

I used a bare wire jumped from the smallest electrolytic bypass to the power pins for the op amps, made a good improvement. The Burson V4 op amps have sounded the best so far.

The servo op amp sounded best with an op627, and 1uf k74 polystyrenes in place of the .47uf box caps, had to be mounted off the board.

Lots of potential I have discovered...


The output resistor can be replaced with a lower value, think I used 18r, Caddock.

Can you atach a scheme with marked changes you've made to the DAC?. wanted to be revised my DAC