Yes, according to datasheet, DVDD must be equal to AVDD or less.
There are two diodes and either one will start conducting @ 0.6V voltage difference.
I'm using the same voltage regulator for DVDD and AVDD. Loads are isolated through SMD NPN transistors. In my case diodes are unnecessary, since difference between DVDD and AVDD is only 0.006V (6mV).
Anyway, YMMV and they can stay to prevent damage to DAC chips.
I can't see the picture. Did you upload it correctly or is there something wrong with my browser?
As it is not straightforward to simply replace the DC-DC converter by a linear regulator (i.e., 7805 or, for lower noise than 7805, an LM317), perhaps someone is aware of a compatible SOIC 8-pin DC-DC converter replacement part with higher switching frequency? Then the switching noise would be easier to filter out with some tantalum and ferrite.
This would avoid the need for an external PSU due to thermal issues with a linear regulator.
And while we're at it, we could actually replace the LM317 that supplies the 1.2V by such a thing. The current savings could then be reused elsewhere inside the box...
(and from what my fingers tell me, it does get quite warm, so the current savinngs could be substantial...)--
Greetz,
MatchASM
Is there any audible benefit to having separate supplies for WM8740's AVDD and DVDD lines as opposed to powering the chips from a single regulator? All I could find on Google is people saying how they use the former or the latter without any mention of difference in SQ.
I imagine so, because otherwise Wolfson would not have reserved two different pins on the package.
In a general sense, separating AVDD and DVDD on an audio DAC is a good idea, especially at high sampling rates and large word lengths such as the 192/24 on the WM8740. The digital signals have a very "rich" spectrum and can easily modulate the audio output signal. Even with separate supplies and appropriate circuit design style, it is still tough to achieve 80dB isolation in a bulk (vanilla) IC process.
The result of all this modulation is lack of clarity in the sound, especially high frequency sounds of large amplitude.
Another way to screw up is improper decoupling of either of the supply rails. I was actually surprised to find out that CA did not put more ceramic/tantalum on them.
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Greetz,
MatchASM
This is good idea! For example LM2672M/LM2675M - frequency more 225 kHz vs. 24 kHz at mc34063.
I have a Dacmagic that I use in my bedroom system and it's a decent little unit. Looking inside it and seeing all the mods and the sheer amount of effort it entails, why no just start with a separate board for something more friendly like a HK Gigawork AD1955? Seems like the work and results obtained are not anywhere near in proportion to the work or expense required and destroy any resale.
Datasheets are looking good; pinning is slightly different, however. So I guess we need to replace the timing capacitor by a resistor (the internal 50k resistor on the sync input looks like it needs another one in parallel, in order to sink aggressor currents).
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Greetz,
MatchASM
Does this "HK Gigawork" of yours include dual WM8740s and Anagram's Adaptive Time Filtering?
If your Mercedes-Benz C-class only has a 1.6L engine, there is no point in turning it into a street-racer, even though it is easier to modify than a Honda Civic Type-R.
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Greetz,
MatchASM
Refering to the datasheets for the two mentioned DACs, I'm not seeing anything that stands out one above the other. The AD1955 is at least current output so that if you wish to use your own I/V rather than the internal opamp then you can.
Edit: noticing in the last page of the CA whitepaper that the higher spec 840C CDP uses the AD1955.
As for the AATF the only thing I've seen about it that shows it's different is the CA white paper on it, some of which does not apply to the Dacmagic and the rest reads as marketing. The 'measured' results they show are obviously from two different measuring systems (no AP log and very different look on the second) and the results are in the -140dB range, clearly inaudible. Got something concrete to show that this system is better, and not just different to any other?
Car analogies never really apply so I ignored that.
I'm sure there are lots of DACs out there with neat datasheets and sh*tty IMD real-world performance.
This I find relevant.
From what I understand, with the AATF module you also get Anagram's CDR and drift correction algorithm. To me this did not read as marketing at all, but it does not bother me at all if you feel differently.
Too bad; I love talking about cars and I think the DAC/engine analogy is rather neat. Of course it makes no sense to have an analogy for convertibles...
The proof of the pudding is in the eating. I think it would be fun to compare the dacmagic to the HKG. Nonetheless, I still feel the ultimate performance ceiling for the dacmagic, given stock DSP and stock DAC-IC, will be better. Not just because I own one and the casing looks rather neat.
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Greetz,
MatchASM
Well, show me the measurements, You can 'believe' all you want. I want data.
How so? That CA choose to use the AD1955 in their higher spec and more expensive implementation of all their chosen technologies rather than the 8740? It tells me that they believe it to be the better DAC.
Comes back to belief vs data. Still seen nothing that *shows* it is superior apart from the assertion of those who invented it and who have paid to use it. The latter might be because of actual performance improvement or simply to differentiate the device in the marketplace.
Sure I love talking about cars too, but I find the analogies between them and audio components tenuous at best.Too bad; I love talking about cars and I think the DAC/engine analogy is rather neat. Of course it makes no sense to have an analogy for convertibles...
I will do thi later as I need another DAC, so I'm going to order the Gigawork board. With everything except a case it is ~25% the cost of a new Dacmagic. My DM was secondhand at about 45% retail because the previous owner bought a CA DVDP. I'll put the DM in my office to run out of the PC.
My feeling is *maybe* for the DSP section, but probably not for the DAC for the reason stated above. The standard DM O/P stage is rather awkward design.
Multitone IMD measurements with complex modulation envelopes? Nobody does that.
It shows me that at the very least CA think it's a decent DAC. Not necessarily better, though.
To quote Feynman, "a lot more is known than is proven." It is indeed belief, but at least it's based on something plausible. If you want proof, I'll gladly let you go ahead and do the measurements.
Please enlighten me how the dacmagic O/P is awkward. Apart from choice of op-amps for cost reasons I find it quite superb.
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Greetz,
MatchASM
My DACMagic is sounding pretty good to me even though I know it's got a basic crystal clock and compromised power supplies. (compared to the 640P or 740P's equivalents). So I'm up for more mods and reading the ideas posted by more experienced forum members.
I did the mod to turn the "USB" input into another digital input - thanks to MatchASM for his feedback. It's quite basic and doesn't change the sound other than not using the 16 bit USB input any more.
There is a Stereophile review with some measurements at Cambridge Audio Azur DacMagic D/A converter Measurements | Stereophile.com. They are not what Brett asked for but may be of interest.
I did the mod to turn the "USB" input into another digital input - thanks to MatchASM for his feedback. It's quite basic and doesn't change the sound other than not using the 16 bit USB input any more.
There is a Stereophile review with some measurements at Cambridge Audio Azur DacMagic D/A converter Measurements | Stereophile.com. They are not what Brett asked for but may be of interest.
4 rectifying diodes -> CRC -> 3 pin regulator used as pre-regulator to reduce ripple & hum -> opamp based regulator -> 7 individual stages to isolate loads (digital chips). On the left side are 6 x +5V outputs, since all 74HC... and 74VHC... chips are supplied with +5V. And one +3.3V output for CS8416 receiver (VA supply).
Regulators for DAC chips are on separate PCB. Existing 7815 regulator is used as preregulator in this case.