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Old 11th September 2002, 05:35 PM   #1
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Default Wolfson WM8746 DAC

Today I was given a brand new cheapie AUS $200 MAKASU DVD-3000A DVD player.
After an hours listening the lid came off and I fitted better quality (2) op-amp supply bypassing and (2) audio output coupling capacitors (Nichicon smps electros) plus 0.1 mFd smd ceramic cap across each new cap.
This I did as a first change before more listening and further mods.
The smd op-amps are 4558 (drop in suggestions ?) so they will likely change, as will more caps.
The result is firmer bottoms and sweeter highs, and overall nicer.
Not too bad really, but maybe it needs a better master clock.
I need to do a back comparison tomorrow to see how it stacks up pleasantness and dynamics and detail wise with respect to my reference souped up old heavy solid Philips player and my factory bog standard (this is deliberate) Marantz CD-46, but certainly before and after mod sounds are different.

I had a close look, and the DA Convertor is an smd 28 pin Wolfson WM8746 containing 3 stereo DA convertors with a bunch of interesting features.
Some features run under pin select stand alone operation, more extensive are under external system uP control (PIC and lcd ?)
These features include interesting things like multiple sample rates and word lenghts, multiple serial data formats, polarity flip for each pair of channels, volume control down to -127.5 dB in 0.5 dB steps for all channels together or individually with zero crossing detection, and the ability to switch each of the three stereo pairs into stereo/reverse/L only/R only/L 2 ch mono/R 2 ch mono/L+R 2 ch mono modes ala old hifi amps, and some intelligent muting functions.

I have no idea of prices or availabilities, but it seems like a most usefull device for stereo or surround systems.
Anybody have experience of this chip ?.

Regards, Eric.
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Old 11th September 2002, 06:13 PM   #2
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I have got excellent support from Wolfson in Scotland. Information about prices and availabilities is on their site.

Have a look at the WM 8740.

I suggest you send them a mail.

Regards
Carl
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Old 12th September 2002, 01:11 AM   #3
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Thanks Carl, any sonic critiques on these Dacs ?.

Eric.
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Old 12th September 2002, 06:53 PM   #4
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Default Daily Improvements

I'll answer that myself.

I listened today and decided that the sound is still not as good as can be, so this evening I replaced all electros on the DAC board with nice quality Nichicon lo-esr smps electros and fitted bypass 0.1 mF ceramics across all of them, and resoldered the Dac chip.
I only got to fit in an hour or so of serious listening, and the sound changed during this burn in, and towards the end the sound got to be good, REALLY REALLY good.
My 12" 3 ways at 4 meters are now resonating chest air and vibrating the soles of my shoes on the carpeted cement floor, and the highs are just great - cymbals ring and ride and vocals are excellent.
This chip so far to my ear is a really good sounding oversampling Dac chip for $8.00.

Eric.
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Old 12th September 2002, 08:39 PM   #5
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My dac is based on the WM8740 and is still under development but I expect it to be as good as anything based on chips by Crystal or AD as the specs are comparable with their best.

I think Sayno OsCon works well for digital decoupling ( or anywhere). Give them a try.

Carl
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Old 13th September 2002, 01:32 AM   #6
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Carl, Good luck with your project - I expect that you will end up with a very nice Dac stage.
The reason I am using the Nichicons is that I can get them from my usual supplier easily and pretty cheap.
I have fitted these caps into other audio stuff and found them to sound very nicely in coupling and bypassing applications.
I'll do some hunting and find out who supplies Sanyo caps locally.
I know the WM chips have very good specs, but more importantly to my ear is that the oversampling noise shaping sounds pleasant with nice highs, as opposed to some others that I do not like such as Panasonic Mash noise shaping.

Eric.
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Old 13th September 2002, 07:39 AM   #7
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Default Decoupling caps...

Not to make some dishonnest ad for myself, but have a look here. Some bypassing configs are tested, and I must say I didn't find the OS-CONs worth their price for digital bypassing. But it's only measurements in a particular application, and no "audio" results still available

Just my $0.02
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Old 13th September 2002, 08:01 AM   #8
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hello,

I live in swden aswell and i like to ask if the dac is for private or professional use? if for private u might want to consider sharing it??

I myself are in the middle of a cs8420 / 43122 project

/micke
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Old 13th September 2002, 08:26 AM   #9
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Hi Eric,

if I understood you correctly, you are using electrolytics bypassed with ceramics as coupling (i.e. DC blocking caps)? I would use neither to handle any audio signal. Mylar or better polyprop are the materials of choice.

If it is a DVD player, there is bound to be a 27 or 54 MHz master oscillator and a PPL that generates the clock for the DAC. This is certainly sub-optimal jitterwise. The way to go would be to have a local oscillator for the DAC. But then you'd need a PLL to generate the 27 MHz so that the rest of the electronics are happy...

Eric
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Old 13th September 2002, 05:11 PM   #10
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Hi Eric,
I have service manuals for this and a couple of other models coming in the next week, and then I will have more info on exactly how the whole thing works.
Without a more detailed look so far or service info knowledge, I agree that I think that there is a jitter thing happening, although Wolfson claim that their oversampling Dac is jitter reducing.
I do feel that a better clock would be a final fix, but so far it is sounding pretty damm good for so far only changing caps and adding bypass ceramics.
This evening I changed the stereo output smd op-amp from the original 4558 to a LM833 to a TL072.
The 833 sounded a bit glassy and smashing glass in the highs, and the TL072 was not too bad, but I need to refit the 4558 to get a proper comparison.
Any suggestions on what is a good drop in replacement/improvement ?.
Any suggestions on a better clocks arrangement ?.

Eric.
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