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pupDAC Step-by-Step Build Thread - Page 11

post #151 of 277
Quote:
Originally Posted by Avro_Arrow View Post
 


My voltages are referenced to Gnd (at the RCA), not from one pin to another.

On the + and - inputs, there was only a couple mV difference in the four pins.

The lowest was 117mV and the high was 119mV. And of course, the +2.5 and

-2.5 supply voltages. The output offset should be less than 10mV but a little

higher is not uncommon in the pupDAC.

Okay, i did this first. Pin 1 & Pin 2 & Pin 5 are 120mV, Pin 6 307mV!!!

 

Quote:
Originally Posted by tomb View Post
 

Here are some suggestions:

 

It's hard to tell - your photos are great - but some of the solder joints may be cold.  In particular, it appears that some of the resistor leads look like they've been poked through the solder.  I'm sure that's not the case, only that it's some indication the joint may be cold.  So, be methodical about it, but start with the through hole resistors and see if you can re-flow the solder on their joints.  For instance, R14 and R15 take the Right channel outputs from the DAC chip directly.  If there's something faulty in the connection there, that may explain the lack of audio output in the right channel.  Go through all the resistors this way, stop, then re-measure with the power off and check for good continuity throughout the circuit.  A way to do this is - with power off - touch one DMM probe to the output pin on the DAC chip, then touch the other probe to the far lead (toward the opamp) of the resistor.  If you can read zero ohms, then things are OK.  Do this for the C3 and C18 mica capacitors, too.  While you're at it - also check L5.  One of the capacitors is blocking it, but it looks a bit dodgy on the right side.

 

Let us know what you find when you have a chance. :)

After that, i reflowed almost every through-hole part, but they were all good. All continuity checks were successful. I re-measured all resistor values for correctness.. no error there. Still no audio on the right output. After getting a little bit upset, i wanted to swap the opamp with the other provided (thanks again tomb for the fast shipping and so on). But as i started to remove the solder, i noticed after heating a pin, the solder kind of flowed beneath the lead. So, i tought rinsing it again with flux and reflow all pins and yes, that somehow did the trick. From the visual perspective, the solder joints looked really good (as far as i can judge that). But now, everything works like a charm!!! Next step will be putting it inside my PPAv2 amp to be used at my workplace, because i'm not allowed to switch my sound card ;)

 

Thank you very much avro and spacially tom for your help and dedication. I really appreciate that!

post #152 of 277

 

Glad to hear you got it figured out!

post #153 of 277
Thread Starter 

YAYYY!!

 

Me too - many thanks for your help, Avro!

post #154 of 277

I've only skimmed through this thread so excuse me if it has been asked before:

 

Is there any way to use some sort of 8-pin socket for the opamp?

 

Also, if I were to build my own chassis for this PCB, how hard would it be to get all the jacks on the same panel?

post #155 of 277
Thread Starter 

Answers below -

 

Quote:

Originally Posted by OJNeg View Post
 

I've only skimmed through this thread so excuse me if it has been asked before:

 

Is there any way to use some sort of 8-pin socket for the opamp?

 

No.  The opamps are specially selected for both their speed and low voltage/rail-to-rail capability.  The opamp in the pupDAC circuit is not being used in the normal sense.  It's actually a differential-to-single-ended converter.  The outputs from the PCM1794 are fully balanced, so a conversion is needed to provide single-ended output.  The opamp in the pupDAC performs this function.

 

Typically, the opamps specified are way too fast, with very high current impulse capability, to be configured in a DIP-8 layout.  In fact, some opamp instability was observed in the pupDAC prototypes (output voltage offset).  It's why there are four through-hole resistors on the bottom of the PCB, where the opamp is located.  The resistor locations cut down on the lead length and trace length to the opamp, promoting stability.  The opamp (OPA2836) may not even be stable if it was offered in a DIP-8 form (it's not).

 

Also, if I were to build my own chassis for this PCB, how hard would it be to get all the jacks on the same panel?

 

Depending on the case you select, it's just wiring - nothing more.


Edited by tomb - 12/3/13 at 6:29pm
post #156 of 277

Understood, thanks.

 

I'm thinking I'll order the short kit + silver Hammond chassis in a few weeks and get it started over the holidays. :)

post #157 of 277

Hey,

Just finished mine but even LED won't light up. Reflowed all pins and SMD parts. Tried with two USB-cables and two laptops.

Checked also for solder bridges under magnifying glass but couldn't spot any

 

Voltages in board:

5V: 1,1

4V5: -0.01

others 0.

 

Guess something is pretty wrong in this...

post #158 of 277
Thread Starter 
Quote:
Originally Posted by berserkir View Post
 

Hey,

Just finished mine but even LED won't light up. Reflowed all pins and SMD parts. Tried with two USB-cables and two laptops.

Checked also for solder bridges under magnifying glass but couldn't spot any

 

Voltages in board:

5V: 1,1

4V5: -0.01

others 0.

 

Guess something is pretty wrong in this...


Yep.  The LED is a direct connection off of the USB jack through L1 and R1, so only the soldering of the USB jack, getting the LED in backwards, or somehow messing up L1 or R1 are the only things to cause it.  I can't say for the rest until we can see the PCB, but almost anything is fixable.:) 

post #159 of 277

Led is OK, still not light up, did some testing and used new LED in case old was damaged somehow.

I would suspect USB-jack to be damaged/faulty, but I don't know how to check/measure that. 

Cleaned and resoldered R1 and L1, still nothing. I'll put some pictures but I'll get to USB-microscope tomorrow so more will follow hopefully..

Board is bit messy, cleaned it bit more after pictures.

 

 

 

 

post #160 of 277
Thread Starter 

I can't tell a whole lot from the pics, except that maybe L1 looks suspect.  If you look on the back of the PCB, the USB jack pin carrying the 5V from the USB buss has a direct trace through L1 to the LED and R1.  There's not much to go wrong there unless L1 or R1 are shorting out or not connecting the trace.  See if you can measure zero resistance from that pin on the USB jack to the first lead of the LED.  If it's not zero, then something's wrong with the connections to L1.

post #161 of 277

double post

post #162 of 277

These two are zero resistance, others aren't.

 

 

Can short in X1 cause these problems? I was inspecting this closer and it seems that some pads possibly had connection to the top of the oscillator..

post #163 of 277
Thread Starter 
Quote:
Originally Posted by berserkir View Post
 

These two are zero resistance, others aren't.

 

 

Can short in X1 cause these problems? I was inspecting this closer and it seems that some pads possibly had connection to the top of the oscillator..


Wrong ones.  Look at the giant trace coming from the bottom left pin in your pic - the far left one in the row of three.  That's the power pin.  Notice the large trace coming off of it and bending all the way around to L1.  L1 connects it to the rest of the trace that then flips around to the other direction at the front edge of the PCB and to the first lead on the LED.  Measure the first lead of the LED to that bottom left pin on the USB jack and see if you get zero resistance.

post #164 of 277

Got mine working. Had little troubles but managed to finish it.

Sound is just amazing, first I was thinking if it can get better than GrubDAC but apparently it can.

Will post picture once I get the case finished..

 

Big thanks to TomB for the product and support.

post #165 of 277
Thread Starter 
Quote:
Originally Posted by berserkir View Post
 

Got mine working. Had little troubles but managed to finish it.

Sound is just amazing, first I was thinking if it can get better than GrubDAC but apparently it can.

Will post picture once I get the case finished..

 

Big thanks to TomB for the product and support.


I'm so glad you got it going!! :D 

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