Wm8742

[lduarte1973]

Is it possible to replace a WM8740 by the new WM8742 in a 740C Cambridge Audio CD player? WM8742 is 16-32bits 192khz and the wm8740 is 16-24 192khz capable.

[elingeniero]

I've been looking at the data sheets. I think (but not positive) that it depends on if the the DAC is being controlled by software or hardware. Doesn't look like it.

For instance in hardware control mode, pins 27 and 26 tells the 8740 what sample rate the audio data is in, whereas pin 27 tells the 8742 what format (PCM or DSD) the audio data is in.

Moreover there are even bigger differences in software control mode.

[InfiniteGain]

Originally Posted by elingeniero

I've been looking at the data sheets. I think (but not positive) that it depends on if the the DAC is being controlled by software or hardware. Doesn't look like it.

For instance in hardware control mode, pins 27 and 26 tells the 8740 what sample rate the audio data is in, whereas pin 27 tells the 8742 what format (PCM or DSD) the audio data is in.

Moreover there are even bigger differences in software control mode.

Hmmm... makes me wonder what Wolfson mean when they claim it is pin-compatible with the WM8740 and WM8741?
Wolfson Microelectronics plc: WM8742

[InfiniteGain]

May wish to read this:
Rega Apollo DAC change to WM8742 - pink fish media

And follow the link to the Wolfson presentation.

[lduarte1973]

I emailed both Wolfson and Cambridge Audio about this , maybe i´ll get an answer soon...

[InfiniteGain]

Originally Posted by lduarte1973

I emailed both Wolfson and Cambridge Audio about this , maybe i´ll get an answer soon...

They should be able to tell you. The Wolfson presentation held the quote that the WM8742 was "totally pin compatible with the WM8741". I infer that to mean backwards compatible.

I don't see anything in the datasheets to suggest there is no compatibility dropiing in the WM742, you just will *NOT likely* get DSD operation from it because you probably don't have a DSD clock in the player.

Let us know what Wolfson and in particular Cambridge Audio say, as I think what benefit (if any) you get is based more on how Cambridge Audio have engineered the player.

[lduarte1973]

" The 740C is designed and made with the WM8740. Our products are not user serviceable, and are not designed to be modified. It is not possible to simply replace a DAC with a newer one, as they will have different circuitry and components and may not be compatible. "

[InfiniteGain]

Originally Posted by lduarte1973

" The 740C is designed and made with the WM8740. Our products are not user serviceable, and are not designed to be modified. It is not possible to simply replace a DAC with a newer one, as they will have different circuitry and components and may not be compatible. "

That sounds like a stock "don't mess with our player" remark. The last part "may not be compatible" means they won't tell you if it is or isn't!! I thought Cambridge Audio were better than that as they seem to have helped people modify the 640P phono stage on another forum.

[lduarte1973]

Unfortunately, there are differences between the functionality of the WM8740 and the WM8742 and there are not completely pin compatible. Also, we do not have information relating to how Cambridge Audio are using the WM8740 within the CD player. Therefore we cannot be recommended replacing the WM8740 with the WM8742.

[InfiniteGain]

Originally Posted by lduarte1973

Unfortunately, there are differences between the functionality of the WM8740 and the WM8742 and there are not completely pin compatible. Also, we do not have information relating to how Cambridge Audio are using the WM8740 within the CD player. Therefore we cannot be recommended replacing the WM8740 with the WM8742.

Hmmm.... I find it hard for them to say they are "not completely pin-compatible" when they use the words "totally pin-compatible" in that presentation of theirs. Also the guy of at PFM managed to change his WM8740 to the WM8741 with just a slight power supply adjustment. I would have thought this was a better option for you anyway as you wouldn't gain anything from the WM8742 and the Cambridge is using Anagram Tech's filtering technology as far as I know, so you have no need of on-chip digital filtering.

It looked to me that pin 27 in hardware mode is held low to signify PCM data, and it detects clock frequency in software mode and automatically switches to bitsream if it 'sees' a DSD frequency clock. Other than that, I didn't see any difference between the WM8742 and WM8741 - and we already know the WM8741 can go in to the Cambridge Audio 640C Mk2.

Perhaps FatMarley at PFM has some info you do not and has had better help from Wolfson - sometimes it depends who answers the support call. It may be worth going on to PFM and sending him a PM about it.