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Old 18th June 2008, 02:57 PM   #81
spencer is offline spencer  Hong Kong
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No plan in near future as I am quite satisfied for the performance of my CD-PRO2 + D1V3 + Jfet pre + F4 + proAc 2.5 clone and there is no hurry for me to upgrade! Just let me enjoy music for a while first.

May be spzzzzkt can offer to us.
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Old 18th June 2008, 09:17 PM   #82
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Photos of D1V3 built by DIYers around the world.

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Old 19th June 2008, 05:19 AM   #83
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those look great finneybear...

no plans to do a vcxo board. the d1 secondary pll is reasonably dependent on the cs8412/4 so limits it's usefulness to d1v3 builders who choose to run newer chips. I'm also more interested in building a d1 that is closer to the Colburn/Pass design - the D1V3 is really very nice but leaves me pondering how the dac would sound with mosfet I/V, 78xx regs, and passlabs approach to supply filtering.
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Old 19th June 2008, 10:40 PM   #84
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Reading up trying to learn something about pcb layout and grounding techniques and came across some interesting references:

1) http://www.hottconsultants.com/pdf_f...ixedsignal.pdf
2) http://www.hottconsultants.com/techtips/tips-slots.html
3) http://www.tentlabs.com/InfoSupport/...decoupling.pdf
4) http://www.sigcon.com/Pubs/edn/multipleadc.htm

These articles drew my attention to what the PCM63 datasheet says in relation to power supplies:

Quote:
Both commons should be connected to an analog ground plane as close to the PCM63P as possible.
I'm possibly missing something here, but the D1V3 layout seems to break the "rule" that agnd and dgnd are to be connected to the same ground plane as close to the chip as possible.

If I'm reading the layout correctly the dac agnd and dgnd only communicate via L21. Because the two sections aren't connected internally, doesn't this mean the ground path for the digital and analog sections of the 4 PCM63 chips describe large loops that intersect at L21? Won't this degrade performance?

Please correct me if I'm misunderstanding something.

cheers
Paul
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Old 19th June 2008, 11:48 PM   #85
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Quote:
Originally posted by spzzzzkt
those look great finneybear...

no plans to do a vcxo board. the d1 secondary pll is reasonably dependent on the cs8412/4 so limits it's usefulness to d1v3 builders who choose to run newer chips. I'm also more interested in building a d1 that is closer to the Colburn/Pass design - the D1V3 is really very nice but leaves me pondering how the dac would sound with mosfet I/V, 78xx regs, and passlabs approach to supply filtering.
1. The merit of simple reclocking circuit is questionable. Most of the time it will simply give you a different sound. One of the better solutions is to build something with FIFO, VCXO, PLL, etc, something similar to the Lavry solution. I know one guy in China is working on this through a FPGA. Or you can take a different route, switch to I2S. Another buy in China is selling an I2S interface board for CD transport. You will have to provide the recipient side yourself. Sure, everything has to start with a good CD transport. This then will be a major upgrade to D1V3.

2. MOSFET probably will give you a warmer, more forward sound, at the cost of some high end ultimate resolution. Yet you will have to know that the signal paths on D1V3 have been highly optimized. They are in the shortest possible paths.

3. LM317 is not necessary better than 78xx. The main difference is the noise level. Those LT devices are definitely good. Another thing is the response time. Fast response time does not necessarily mean better sound. So it's always worth of a try yet my take is that the output cap is more important than the active device itself. This is especially for digital power supply. We chose LM/LT devices on D1V3 simply because of the lower noises. As for the analog output power supply, the one we put in is fairly good already. You can try other solutions to see whether they sound better to you. The options of tuning in definitely plenty.

4. One major power supply upgrade I do recommend is to add one more power filtering stage. Separate transformers for each power rail. About 20,000-40,000uf power filtering for each rail. Use Rifa, BHC, or Epcos caps. Use big fat soft recovery diodes. I even dont mind if you use chokes. Pack all of these in a separate box. You may want to parallel the caps with smaller ones to speed them up. Keep the power caps on the DAC board as they are.

5. Try BlackGate N for the output cap. Big film caps have microphonic problems. Film caps with oil filled are the best yet you can hardly find affordable 10uf oil caps.

6. Some have replaced resistors on the analog output paths with SMD parts. Be sure to get the tantalum film ones. Definitely better characteristics than through hole parts.

7. After everything is done, seal the analog output parts with epoxy mixed with thermal paste. Cover the section with copper box, if you can.

8. At last, shield the board with EMI absorbing sheets. No need to get the super expensive multi-layer ones.

I can keep going and going....
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Old 20th June 2008, 12:22 AM   #86
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Quote:
Originally posted by spzzzzkt
[
I'm possibly missing something here, but the D1V3 layout seems to break the "rule" that agnd and dgnd are to be connected to the same ground plane as close to the chip as possible.

If I'm reading the layout correctly the dac agnd and dgnd only communicate via L21. Because the two sections aren't connected internally, doesn't this mean the ground path for the digital and analog sections of the 4 PCM63 chips describe large loops that intersect at L21? Won't this degrade performance?

Please correct me if I'm misunderstanding something.

cheers
Paul [/B]
Well, rules are just, rules. Not even mention those rules are not universal.

PCM63's datasheet says the benefit for separate analog and digital power supplies is minimal. This is hardly a surprise for most chip designers. Well, whatever power supply it will be, the ground planes are all connected together in most chips. In other words, when you do the layout floor planning for a PCM63 DAC, you will have to keep in mind that the analog and digital grounds are already connected inside the chip.

Any ground plane has current flowing. I.e. different points at the ground plane may have different voltage. One goal of layout is to eliminate the voltage difference and to provide paths to dump those currents as soon as possible.

What we did on D1V3 are:

1. Put ground planes on the top of PCB, instead of bottom. Along with the chassis, this will provide some extent of shielding for signals running on the other side of the PCB.

2. Divide the analog and digital ground roughly in two big planes. The boundry runs across the center of PCM63 chips.

3. We know that the grounds are connected inside PCM63s. Along the plane boundary, we also provide a few connectors through beads. Now we know any current between analog and digital grounds will flow through those pipes.

4. Since you know where those pipes are, you can provide adequate shielding around the pipes so the ground current will not interfere with other circuits. The beads will absord some HF noise current, too.

5. Now here's the trick. You may find tiny holes around the very corner of each ground plane, or you can scratch off the ink to expose the copper. Solder a thin silver wire to this hole, then run the other end to the middle of the ground plane. Repeat this to the rest three corners. Now solder all four wires together in the middle of the plane. You should be able to find a screw hole or whatever around the center. Solder the wires to this contact point. Now you have done the star ground for one plane. Repeat this to another plane. At the end you will have 2 star grounds. Either you can connect them to chassis separately or to a single point at the chassis. This star ground will be the short current dumping path.

6. Sure, you can make more star grounds. Even better, adding by-pass caps or inductors to absorb ground current.

7. We have done other tricks on the layout so most people cant see the need to go to this length. This is why we didnt mention it... yet since you are asking...

Oh, BTW, have you noticed right beside every IC there's a small hole? You stick a copper foil to the top of the chip, solder a wire to it then connect it to this hole. Nice?
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Old 20th June 2008, 03:14 AM   #87
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Finneybear,

Could you explain why you claim the grounds are connected inside the pcm63??? If this were the case there should be close to 0ohm resistance between pins 7 & 12. On the chips I have I measure OL, which indicates there is no connection between agnd and dgnd.


Paul
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Old 20th June 2008, 05:01 AM   #88
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Quote:
Originally posted by spzzzzkt
Finneybear,

Could you explain why you claim the grounds are connected inside the pcm63??? If this were the case there should be close to 0ohm resistance between pins 7 & 12. On the chips I have I measure OL, which indicates there is no connection between agnd and dgnd.


Paul
You can not just move the board level concept into the silicon.

Basically there are certain safeguards built in around the pins. Also for different voltage planes, usually they are connected though diode bridges. Chip designs have to deal various conditions. For instance, if pin 7 and 12 are connected together externally, and the analog 5V comes in first, this will create a voltage jump in the digital domain and fry the circuit.

Some DAC chips are particularly fragile. CS43122 is one famous example. If you have separate power supplies for digital and analog, the chip will get fryed easily.

-finney
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Old 20th June 2008, 05:43 AM   #89
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Quote:
Originally posted by finneybear


You can not just move the board level concept into the silicon.

Basically there are certain safeguards built in around the pins. Also for different voltage planes, usually they are connected though diode bridges. Chip designs have to deal various conditions. For instance, if pin 7 and 12 are connected together externally, and the analog 5V comes in first, this will create a voltage jump in the digital domain and fry the circuit.

Some DAC chips are particularly fragile. CS43122 is one famous example. If you have separate power supplies for digital and analog, the chip will get fryed easily.

-finney
But that begs the question: how can you say the gnd's are internally connected or not if you cannot directly test?
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Old 20th June 2008, 06:19 AM   #90
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Quote:
Originally posted by spzzzzkt


But that begs the question: how can you say the gnd's are internally connected or not if you cannot directly test?
I am afraid that you missed my point. They are connected inside through certain circuit, for instance, protection bridges hence you can not just measure the resistance between the two pins to decide whether they are connected.

Or take it this way. inside PCM63, the digital domain has lots of switches keep switching quickly. These will create lots of bounces on the ground plane. The analog domain has lots of bounces, too, when the R2R network is working. Definitely it will be nice to have separate power supply loops for digital and analog so you can reduce those circuit noises more effectively. Yet why BB claimed that you would not get any benefit with PCM63? Can you think of any reason?
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