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post #271 of 277

Your lowest voltage is 127.5mV.

You want to adjust the value of the others to match this value.

The easiest way to figure out what value you need is to get

a 200k 20k trim pot and install it across the Riv resistors one at

a time. Adjust the trim pot until the voltage reads 127.5mV.

Unsolder the trim pot and measure the resistance. Find the

closest standard value and solder this on top of the Riv you

just measured. Repeat until all the Riv read 127.5mV.


 

This process will account for tolerance in the Riv resistors

and the tolerance of the PCM1794a.

 

Edit: changed trim pot value.

The expected values of the parallel trim resistor

will be in the 1k to 10k range.


Edited by Avro_Arrow - 5/11/14 at 4:26pm
post #272 of 277

As a test, I placed a 10K resistor (in parallel) on R14 and brought down the DC offset to around 3 mV. The noise was still there, and when I ran RMAA it reported way lower specs that what I'd originally measured. The dynamic range was around 70, noise around 70, crosstalk in the 60s, etc. Am I doing something wrong?

post #273 of 277

After flirting with the idea for quite a while - I caved and ordered my pupdac kit this afternoon.  Really looking forward to giving this build a go!  I have at least one successful smd project under my belt at this point (agdr's booster) and a wire se-se in progress (presently on hold pending a decision as to an enclosure), so hopefully I'm adequately experienced to manage the oscillator and bb 1794.  I suppose we shall see!  Will make sure to report back with either requests for help or confirmation of success (fingers crossed for the latter).

 

Thanks for the wonderful thread and build guide!  I love my current bb 1793 based dac and am hopeful that this will be a similar flavor.  As an aside, is anyone else contemplating the possibility of dropping their pupdac and a doodlebug in a single chassis? 

post #274 of 277
Thread Starter 
Quote:
Originally Posted by skeptic View Post
 

After flirting with the idea for quite a while - I caved and ordered my pupdac kit this afternoon.  Really looking forward to giving this build a go!  I have at least one successful smd project under my belt at this point (agdr's booster) and a wire se-se in progress (presently on hold pending a decision as to an enclosure), so hopefully I'm adequately experienced to manage the oscillator and bb 1794.  I suppose we shall see!  Will make sure to report back with either requests for help or confirmation of success (fingers crossed for the latter).

 

Thanks for the wonderful thread and build guide!  I love my current bb 1793 based dac and am hopeful that this will be a similar flavor.  As an aside, is anyone else contemplating the possibility of dropping their pupdac and a doodlebug in a single chassis? 


You won't have any issue with the oscillator.  It's only trouble when people use too much solder and get some on the top - that shorts it out. The bb1794 is a different story. It's no different than soldering a PCM2702 on the Alien DAC or BantamDAC.  Still, it can be a challenge.  Check all the methods used for SMD soldering for the AlienDAC, BantamDAC, etc.  Also check the temperature on your iron.  I've soldered one perfectly before and still had it fail because the iron was too hot and fried the chip on the inside. 

post #275 of 277
Quote:
Originally Posted by tomb View Post


You won't have any issue with the oscillator.  It's only trouble when people use too much solder and get some on the top - that shorts it out. The bb1794 is a different story. It's no different than soldering a PCM2702 on the Alien DAC or BantamDAC.  Still, it can be a challenge.  Check all the methods used for SMD soldering for the AlienDAC, BantamDAC, etc.  Also check the temperature on your iron.  I've soldered one perfectly before and still had it fail because the iron was too hot and fried the chip on the inside. 

Thanks for the info and advice tomb! I was somehow confusing the 2707 and oscillator, but having cleared that up, it is good to know that I should be careful to avoid getting any solder on the top of the oscillator. I will also be doubly careful to avoid cooking the 1794.
post #276 of 277

That was my experience too, oscillator was no problem at all, it was the 1794 that proved to be the most challenging.

post #277 of 277
Thread Starter 
Quote:
Originally Posted by skeptic View Post
 
Quote:
Originally Posted by tomb View Post


You won't have any issue with the oscillator.  It's only trouble when people use too much solder and get some on the top - that shorts it out. The bb1794 is a different story. It's no different than soldering a PCM2702 on the Alien DAC or BantamDAC.  Still, it can be a challenge.  Check all the methods used for SMD soldering for the AlienDAC, BantamDAC, etc.  Also check the temperature on your iron.  I've soldered one perfectly before and still had it fail because the iron was too hot and fried the chip on the inside. 

Thanks for the info and advice tomb! I was somehow confusing the 2707 and oscillator, but having cleared that up, it is good to know that I should be careful to avoid getting any solder on the top of the oscillator. I will also be doubly careful to avoid cooking the 1794.

 

 

Quote:
Originally Posted by mcandmar View Post
 

That was my experience too, oscillator was no problem at all, it was the 1794 that proved to be the most challenging.

Yep.

 

The PCM2706/7 should not be an issue, either.  The issue with the PCM2707 is lining it up on all four sides with the pads.  If you get it wrong, you can re-position it.  Just make d*mn sure you don't solder a second pin until you're completely satisfied that all the pins on all four sides are lined up.

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