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Old 27th April 2013, 08:19 AM   #21
McGyver is offline McGyver  Poland
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There is another aspect of NOS not mentioned here yet. Removing digital filter forces to heavy analogue filtering. And it needs parts, parts, parts. The heavier filtering, the more parts needed. And each little part affects the sound. Of course one can put in Duelund capacitors and Caddock resistors, but it costs fortune and are physically big like dinosaurs.
So I prefer to use the best digital filter I can achieve and use only one best capacitor I can buy per channel.

So I suppose the reason of Audio Note DAC 1.1x sound failure lays in upper right corner of this green PCB:

Click the image to open in full size.

There is analogue filtering based upon some cheap Philips MKT capacitors. That must affect the sound by much.
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Old 27th April 2013, 08:38 AM   #22
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I suspect the reason this sounds poor is the grounding - I can only see a single ground plane. DAC grounding for decent sound is an art. The grounding is going to make a bigger difference to the sound than the caps - by all means change the caps (NP0 ceramics sound fine to me and are much cheaper than the currently fashionable boutique caps) but only after optimizing the grounding and supplies. I can't see any local regulation for the DAC itself, that's not a good sign.

Oh and if that large toroid is an S/PDIF transformer, change it to something smaller and lower capacitance.
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Old 27th April 2013, 09:20 AM   #23
McGyver is offline McGyver  Poland
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Look at this:

Click the image to open in full size.

I don't suppose it has any better grounding than that in Audio Note DAC 1.1x.
The power supply is also very primitive, only three ugly regulators 7805/7905.
With this simple PCB I achieved very good sound with passive I/V conversion and simple tube gain stage, no analogue filtering at all. Hardly played with this PCB. The signal capacitors at the output of tube stage makes HUGE difference in sound quality. Also the resistors in I/V conversion makes big difference. The type of regulators and capacitors in power supply makes very little difference, or even no difference at all. The rectifier type makes significant difference and SBYV27 I found best.

So, in general, I dissagree the grounding issue could do so big havoc in sound of AN DAC1.1x and I persist in that the poor analogue filtering was a cause.
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Old 27th April 2013, 09:31 AM   #24
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That board looks to have much better grounding than the earlier one. There's a digital ground (to the right) and thick tracks (on the left) which I take to be grounds. Not at all hard to see why this one sounds better. I can't see the tracks on the underside though - in particular the output tracks for 0V need to be starred.
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Old 27th April 2013, 09:42 AM   #25
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Quote:
Originally Posted by abraxalito View Post
That board looks to have much better grounding than the earlier one. There's a digital ground (to the right)
That is not ground, that is +5V supply line.
Quote:
and thick tracks (on the left) which I take to be grounds.
Those are not grounds, those are +5V and -5V supply lines.
Quote:
Not at all hard to see why this one sounds better. I can't see the tracks on the underside though - in particular the output tracks for 0V need to be starred.
No star grounding on underside.
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Old 27th April 2013, 09:49 AM   #26
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Thanks for your corrections - so is the underside a continuous ground plane? I note that there are three individual power supplies - where do they connect together?
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Old 27th April 2013, 09:56 AM   #27
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Originally Posted by McGyver View Post
I have this DAC board with passive I?V and tube stage and it sounds heavenly, so I definitive stopped to search any digital source.

Hi, are you taking advantage and using both (+ and -) signals from your PCM1798 into your tube output stage or just one phase of the signal?
can you share a simple basic schematic and what type of tube are you using for I/V and gain stage? I might try this diy project to compare it to an CS4397/8
Thanks
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Old 27th April 2013, 10:04 AM   #28
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The underside are two continuous ground planes tied together between regulators. The border line lies between filter and DAC.
The digital and analogue ground pins of AD1865 are tied together at the chip, not according to grounding recommendations stated in the datasheet. So this PCB is very ugly designed, but the ground issues could not destroy sound quality. I was to lazy to make it from scratch only to taste AD1856 sound.

By the way, I always completely remove S/PDIF transformers as they affects the sound quality.
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Old 27th April 2013, 10:24 AM   #29
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Quote:
Originally Posted by luxury54 View Post
Hi, are you taking advantage and using both (+ and -) signals from your PCM1798 into your tube output stage or just one phase of the signal?
I tried to use both phases of the signal from DAC, but found no advantage in sound quality. On the contrary, there was degradation due to more complicated analogue stage. So I finished with taking signal from one phase, and the opposite phase is only loaded by I/V resistor to the ground.
Quote:
can you share a simple basic schematic and what type of tube are you using for I/V and gain stage? I might try this diy project to compare it to an CS4397/8
Thanks
The schematic is straightforward. Very similar to that:
Click the image to open in full size.
The signal from conversion resistor is tied to the grid.
I'm using 6DJ8 valves, 180V mosfet regulated supply, 8k2/2W anode resistor, 150ohm cathode bias resistor (unbypassed by capacitor) and 15k/2W cathode resistor in the cathode follower.
The picture omits output signal capacitor (at least 0,47uF Mundorf silver in oil or better, that's essential) and resistor (100k or more) from output to ground. Hope this is clear enaugh.
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Old 27th April 2013, 10:41 AM   #30
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thank you very much for your quick answer
Don't know if I remember well but seems like the tube stage used to invert the phase of the signal so are you using only the L- & R- (since this will be reverted)?
so this would mean that you are using L+ & R+ to GND via the I/V resistor? of what value is this I/V resistor you are using?
I have already a tube output for CS4397 but with 1 x russian 6N6P tube and I also have a similar tube output for TDA1541A using 2 x 6N2P russian tube (a la lampizator design)...do you think that changing these values of components that you gave here might worth a try using that kind of tube only as a quick and dirty solution for the PCM1798 ? (it would be just for a quick comparison and later I would build a separate circuit if it would be worth it soundwise)
Many thanks!
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