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pupDAC Step-by-Step Build Thread - Page 22

post #316 of 321

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Edited by nivz - 1/28/15 at 11:28pm
post #317 of 321
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Quote:
Originally Posted by nivz View Post
 

Thanks for the advice TomB.. I cleaned the board with flux cleaner and deionised water, let it dry under a bulb for about 12hrs.. the problem is still there.. On the PCM1794, There's a bridge on pins 11 and 12, I've scratched the soldermask on the via next to these pads so it's impossible to remove that bridge now, on the schematic these two pins are grounded (FMT0 and FMT1), So I left the bridge as it is.. I didn't think this could be the problem as those two pins are connected to the same via (one I managed to scrape the soldermask off) that goes to C8 on the other side anyway...

 

I'm very new at this so I don't know how I should go about checking if a cap is shorting, can I just check the voltage across every cap? I'll try to post some photos if I can get something to focus close enough to see the details of the board.. Thanks again!

 

Edit:

 

Pics:

1794

[IMG]http://i57.tinypic.com/so4tqh.jpg[/IMG]

 

2707

[IMG]http://i62.tinypic.com/2vw8ep5.jpg[/IMG]

 

Board top

[IMG]http://i62.tinypic.com/qnpqmt.jpg[/IMG]

 

Board bottom

[IMG]http://i59.tinypic.com/kq2qs.jpg[/IMG]


To tell the truth, I don't see any issue with the PCM chips.  Another thing that can cause the symptoms you describe is the opamp.  Are you certain everything is clean and dry around it?  The fact that you haven't trimmed any leads is suspect.  Conceivably, those could be touching something and arcing when you're trying to operate the DAC.  Also look for anything that might be shorting right around the opamp.  It looks like you used the OPA2835.  The 2836 is much, much better.

post #318 of 321
Quote:
Originally Posted by tomb View Post
 


To tell the truth, I don't see any issue with the PCM chips.  Another thing that can cause the symptoms you describe is the opamp.  Are you certain everything is clean and dry around it?  The fact that you haven't trimmed any leads is suspect.  Conceivably, those could be touching something and arcing when you're trying to operate the DAC.  Also look for anything that might be shorting right around the opamp.  It looks like you used the OPA2835.  The 2836 is much, much better.


I've checked around the opamp and I can't see anything that might be shorting.. I'll trim the leads a bit closer to the joints. Could you please tell me if there should be a voltage across the mica caps? they both have 130mV on both sides of the cap, reference to ground. (and 0V across the caps). I can't think why I used the 2835 :s.. maybe mouser didn't have it instock at the time, but I will replace it with a 2836..

 

Thank you so much for taking the time to assist me :).

post #319 of 321
Thread Starter 
Quote:
Originally Posted by nivz View Post
 
Quote:
Originally Posted by tomb View Post
 


To tell the truth, I don't see any issue with the PCM chips.  Another thing that can cause the symptoms you describe is the opamp.  Are you certain everything is clean and dry around it?  The fact that you haven't trimmed any leads is suspect.  Conceivably, those could be touching something and arcing when you're trying to operate the DAC.  Also look for anything that might be shorting right around the opamp.  It looks like you used the OPA2835.  The 2836 is much, much better.


I've checked around the opamp and I can't see anything that might be shorting.. I'll trim the leads a bit closer to the joints. Could you please tell me if there should be a voltage across the mica caps? they both have 130mV on both sides of the cap, reference to ground. (and 0V across the caps). I can't think why I used the 2835 :s.. maybe mouser didn't have it instock at the time, but I will replace it with a 2836..

 

Thank you so much for taking the time to assist me :).


I don't have one apart to measure right now, but any capacitor in a live circuit should read zero DC volts.  That's the purpose in many instances - they block DC, but allow AC current to flow.

 

The 2836 is very much superior, but maybe you should try to get rid of the ticking and noise before changing out the opamp.  The reason I mentioned the opamp is that if it is oscillating, it can also cause the ticking and noise that you describe.  I couldn't see the resistor pads very clearly in your photo and thought you might have some shorting in that area.  You might check to see if the opamp is getting hot?

 

If that doesn't work, I would suggest trying to re-flow the solder on the simpler parts - don't mess with the PCM chips or the TPS regulators.  See if that helps, first.

post #320 of 321
Quote:
Originally Posted by tomb View Post
 


I don't have one apart to measure right now, but any capacitor in a live circuit should read zero DC volts.  That's the purpose in many instances - they block DC, but allow AC current to flow.

 

The 2836 is very much superior, but maybe you should try to get rid of the ticking and noise before changing out the opamp.  The reason I mentioned the opamp is that if it is oscillating, it can also cause the ticking and noise that you describe.  I couldn't see the resistor pads very clearly in your photo and thought you might have some shorting in that area.  You might check to see if the opamp is getting hot?

 

If that doesn't work, I would suggest trying to re-flow the solder on the simpler parts - don't mess with the PCM chips or the TPS regulators.  See if that helps, first.

 

Hi tomb,

 

Apologies for not replying for a long time, I only got around to looking at the pupdac again today. And I figured out what it was. The noise comes from my wifi signal.. As soon as I dropped the output power of the router, the noise from the pupdac was completely gone. If I increase the power, noise comes back, so it definitely is the wifi signal.

 

I don't have the case for the pupdac, but I'm guessing when inside the metal enclosure this won't be an issue. I will try and mount it inside a metal housing to make sure that solves the issue before I order the custom made ones from yourself.  I really appreciate you taking the time to reply to my earlier posts. Hopefully this might help someone with a similar issue down the line.

 

It also picks up noise from a wireless keyboard and a mouse to lesser extent, moving the receivers well away from the dac got rid of a screeching noise it makes when the mouse was moved and a very low ticking noise from the keyboard. It is pretty much dead silent at this point.

 

I've also got the 2836, can't wait to swap it on and see what the difference will be. Even as it is I'm amazed at the sound quality!

 

Best regards,

 

Nivz.


Edited by nivz - Yesterday at 5:41 am
post #321 of 321
Thread Starter 
Quote:
Originally Posted by nivz View Post
 
Quote:
Originally Posted by tomb View Post
 


I don't have one apart to measure right now, but any capacitor in a live circuit should read zero DC volts.  That's the purpose in many instances - they block DC, but allow AC current to flow.

 

The 2836 is very much superior, but maybe you should try to get rid of the ticking and noise before changing out the opamp.  The reason I mentioned the opamp is that if it is oscillating, it can also cause the ticking and noise that you describe.  I couldn't see the resistor pads very clearly in your photo and thought you might have some shorting in that area.  You might check to see if the opamp is getting hot?

 

If that doesn't work, I would suggest trying to re-flow the solder on the simpler parts - don't mess with the PCM chips or the TPS regulators.  See if that helps, first.

 

Hi tomb,

 

Apologies for not replying for a long time, I only got around to looking at the pupdac again today. And I figured out what it was. The noise comes from my wifi signal.. As soon as I dropped the output power of the router, the noise from the pupdac was completely gone. If I increase the power, noise comes back, so it definitely is the wifi signal.

 

I don't have the case for the pupdac, but I'm guessing when inside the metal enclosure this won't be an issue. I will try and mount it inside a metal housing to make sure that solves the issue before I order the custom made ones from yourself.  I really appreciate you taking the time to reply to my earlier posts. Hopefully this might help someone with a similar issue down the line.

 

It also picks up noise from a wireless keyboard and a mouse to lesser extent, moving the receivers well away from the dac got rid of a screeching noise it makes when the mouse was moved and a very low ticking noise from the keyboard. It is pretty much dead silent at this point.

 

I've also got the 2836, can't wait to swap it on and see what the difference will be. Even as it is I'm amazed at the sound quality!

 

Best regards,

 

Nivz.

 

Thanks for your kind comments.  I'm glad you found out what's wrong.

 

Just and FYI, but here's what is next to mine (or within 3 feet):

  1. PC
  2. Two LCD monitors
  3. Wireless home phone
  4. LAN wireless router
  5. Cable modem, also with wireless router
  6. Wireless keyboard
  7. Wireless mouse

I don't have a problem with the PupDAC in its case. ;)

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