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Alien DAC v1.1 Construction Thread - Page 23

post #331 of 1560
9/3/06 at 4:39pm
On page 2 of the PCM2702 datasheet, min analog output load impedance is listed at 5kohm.
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post #332 of 1560
9/3/06 at 5:56pm
I have the same problem as well. I thought it was a bad cap or something, but since you guys have the same problems, it may just be that headphones can't be driven directly off the DAC.
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post #333 of 1560
9/3/06 at 10:28pm
something irrelevant...

Somebody told me that the analog output must be passed through "low pass filter" to farther reduce noice...is it correct? does alien dac has something like that?

the only "filter" i know in the ouput stage that alien dac uses is the CL/CR capacitors...
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post #334 of 1560
9/3/06 at 11:01pm
Quote:
Originally Posted by abcheng
I have the same problem as well. I thought it was a bad cap or something, but since you guys have the same problems, it may just be that headphones can't be driven directly off the DAC.
Theo nly 'problem' you guys are having is not understanding that it is not designed to drive headphones! You need to use amplification. It's only a line level signal.
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post #335 of 1560
9/4/06 at 12:28am
Quote:
Originally Posted by mikemacwillie
Theo nly 'problem' you guys are having is not understanding that it is not designed to drive headphones! You need to use amplification. It's only a line level signal.
I realize that now. It was just that I was testing out the DAC with headphones just to see if I built the DAC properly and happened to notice that the output was distorted at higher volumes.

For anyone who soldered the 2702 chip the wrong way stupidly like me on one of their boards, is it possible to desolder the chip and solder it back in the correct way? If so, please enlighten me .
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post #336 of 1560
9/4/06 at 1:36am
With the correct tools, yes.

Chances of the average DIYer having a hot air SMT rework station.. slim.
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post #337 of 1560
9/4/06 at 5:31am
Quote:
Originally Posted by abcheng
I realize that now. It was just that I was testing out the DAC with headphones just to see if I built the DAC properly and happened to notice that the output was distorted at higher volumes.

For anyone who soldered the 2702 chip the wrong way stupidly like me on one of their boards, is it possible to desolder the chip and solder it back in the correct way? If so, please enlighten me .

If you have a hot air gun, then you can try to melt the solder on the pins and remove the pcm2702. This will be very difficult to do, you should be very pacient and prepare yourself to ruin a board and chip.
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post #338 of 1560
9/4/06 at 5:48am
If ruining the board is a concern just cut the chip off.
If salvaging the chip is the priority use the big blob of solder technique.

(fill all of the gaps between the leads on one side of the chip with solder and gently lift that side of the chip off the board, repeat for the other side... the caveat here is you will lift every pad off the board that is not connected to anything)

Of course you could always bake it to.....
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post #339 of 1560
9/4/06 at 6:47am
Quote:
Originally Posted by MisterX
If ruining the board is a concern just cut the chip off.
If salvaging the chip is the priority use the big blob of solder technique.

(fill all of the gaps between the leads on one side of the chip with solder and gently lift that side of the chip off the board, repeat for the other side... the caveat here is you will lift every pad off the board that is not connected to anything)

Of course you could always bake it to.....
Don't forget that this operation should be done fast. You can't apply too much heat to DAC chip or it will certainly get damaged. In the PCM2702 datasheet you should find the maximum solder temperature and time. Respect these values and you should be fine!
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post #340 of 1560
9/4/06 at 10:01am
The size of the chip can help to possibly unsolder it safely...

fill with solder both sides of the chip pull gently the chip from one side...(with tweezers or with your fingers) move the soldering iron back and forth
until the chip starts moving from one side...after you unsolder the first side
grab the chip with tweezers or your hand and do the same thing from the other side.

It is possible that you can lift some pads too...or you might get burned if you use your fingers.


In this way i have successfully removed very small chips.



something irrelevant...

Somebody told me that the analog output must be passed through "low pass filter" to farther reduce noice...is it correct? does alien dac has something like that?

the only "filter" i know in the ouput stage that alien dac uses is the CL/CR capacitors...
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post #341 of 1560
9/5/06 at 6:27am
Regarding the Cristal section, some questions:

The support site says that the cristal should have a load capacitance of 30pF, but this exact value is not available. Is it better to go with 20pF or 32pF?

The pcm2702 datasheet says that the cristal capacitors(C11,C12) value is related to the capacitance of the cristal. If I go with the 20pF one, should I change the value of those caps?

What are the advantages of using an external clock? How much would this cost, are there available units for sale? Does anyone have any info about this?

Manuel
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post #342 of 1560
9/5/06 at 6:38am
Quote:
Originally Posted by MisterX
Ohhhhhh, Mouser now stocks Os-Cons?

When did that happen?
MisterX, could you provide a link to these caps? They are suposed to be very good for digital decoupling right?
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post #343 of 1560
9/5/06 at 6:43am
I asked that a few pages back, didn't get a clear cut reply as to how it all works, however robzy was of some help.

I personally went with 32pf crystal and 33pf capacitors. I think that's what some others have done.

I believe if you chose a 20pf crystal you'd need capacitors around that value, so 18, 20 or 22pf.

I asked someone about it, according to them at that frequency the difference between a 30pf and 32pf with the capacitors meant for 30pf would be insignificant and wouldn't alter the freqency(or pull it off or something like that), which you can only do slightly anyway. Well something to that effect. 20pf may be a different story.

Well that's about all I can tell you.
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post #344 of 1560
9/5/06 at 12:27pm
MixterX could you post the exact measurements of the usb connector in the front panel?

I want to design a FPE panel but don't want to risk ordering without being 100% sure that it will fit.
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post #345 of 1560
9/5/06 at 12:57pm
Quote:
Originally Posted by MASantos
MixterX could you post the exact measurements of the usb connector in the front panel?
Not trying to be a pain but do you have any reason to doubt the data sheet?
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