Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › pupDAC Step-by-Step Build Thread
New Posts  All Forums:Forum Nav:

pupDAC Step-by-Step Build Thread - Page 16

post #226 of 230
Thread Starter 
Quote:
Originally Posted by COOKIESnPIE View Post
 

A "Bottlehead Crack" and a profile pic of Rob Ford? Beautiful.

 

Jokes aside, the 4.75V may not be problem but my DC offset is way off.


I agree that offset is way too high.  I'm at a loss to really pick out anything in your pics, though - except the resistors.  Cobaltmute spec'd the resistors around the opamp at 1% tolerance.  Those aren't V-D RN50's that you've used, so I'm not sure if they're in the recommended tolerance.  Just an FYI, but even Tangent used to (still does?) have articles online about matching resistors around an opamp for ensuring the minimum in offset with his amps designs.  Matching resistors used to be de riguer when the CMoy, PIMETA, and PPA were first in vogue (not that they still aren't).  Cobaltmute even designed the very critical resistors to be installed on the PCB bottom - right next to the opamp - in an effort to reduce lead lengths and potential oscillation issues.  The pupDAC will definitely result in opamp oscillation (especially with the OPA2836) if everything is not just so-so with the resistors and lead lengths.

 

I'm not saying for sure that's what's going on - it's still only a guess.  Perhaps the resistors could be causing the issue and maybe the opamp is oscillating.  Strange things can go on when that happens, including ticking sounds when the oscillating opamp causes regular/intermittent capacitor discharges.


Edited by tomb - Yesterday at 6:39 pm
post #227 of 230

They're 1% KOA metal films, not "military grade" though. I might be able to get some more accurate resistors near the opamp for a spin, but besides from that I don't know where to look either. I spoke to someone in the industry before building this and they said that rarely you need mil grade resistors unless you need high reliability - just the right tolerances are fine. He could be wrong though...;)

What's with the lead lengths?

post #228 of 230

Is anyone using the pupDAC with JRIVER and Windows 8?

What is the optimal setting?  I'm finding WASAPI EVENT STYLE to be a little unreliable, so currently use the DIRECT SOUND with 0.10s buffer and everything upsampled to 96khz - any others using similar settings?

post #229 of 230
Thread Starter 
Quote:
Originally Posted by COOKIESnPIE View Post
 

They're 1% KOA metal films, not "military grade" though. I might be able to get some more accurate resistors near the opamp for a spin, but besides from that I don't know where to look either. I spoke to someone in the industry before building this and they said that rarely you need mil grade resistors unless you need high reliability - just the right tolerances are fine. He could be wrong though...;)

What's with the lead lengths?


Well, "someone in the industry" may not know about mismatched resistors on a sensitive opamp.  It's not necessarily the precision of the resistors, although that buys you some consistency from resistor to resistor with the same rating.  It's the differences between two resistors of the same rating that can cause offset when applied to the two different Left and Right channels.  For instance, a 100R resistor at 1% precision may be 99 or 101 ohms, a 1K resistor might be 990 vs. 1010 at 1% and so forth ...  Differences of that magnitude can definitely cause offset.

 

You might try measuring the resistors and see if you get a difference in the same rating resistor from one channel to the other channel.

 

Actually, this can apply to solder joints, too.  A few sub-standard joints that may predominate in one channel over the other can combine to increase the resistance in that channel.  That might result in the offset, too.  It kind of explains why two people can build the same thing with the same parts and yet get two different performance results.  It's also why re-flowing solder joints over an entire PCB can sometimes result in fixing a problem. ;)

 

Again, these are guesses ...  

post #230 of 230

Hooked it up to my 17" MacBook Pro tonight and got some new measurements.

 

5V = 4.989V

-5V = -4.9702V

-2V5 = -2.4890V

2V5 = 2.4897V

4V5 = 4.7235V

3V3 = 3.308V

R = 1.04mV offset

L = 0.1mV offset

 

All looking great!

 

Hooked it up to my work 15" MacBook Pro which was had a charger hooked up.  Fed it through my KSA5 clone amp.  With Monoprice 8323 'phones I can hear ticking in both channels from 50%+ volume.  With AT ESW9 'phones it starts about 65%+ volume.

 

Looking forward to trying the Doodlebug!

New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › pupDAC Step-by-Step Build Thread