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Alien DAC v1.1 Construction Thread - Page 100

post #1486 of 1560
1/9/09 at 10:11am
Quote:
Originally Posted by Richi View Post
Thanks for the tip about the hotfix. Sadly after installing this the problem still persists. Vista recognizes a device but labels it unknown in device manager. I have been through all connections again and checked my work and it all looks ok. Does this problem sound familiar to anybody and would you most likely put this down to a driver/OS problem or could it be a problem with the build of the dac?

Cheers.
Rich
I might try reflowing all your joints on the USB connector. You might have a cold joint affecting the pull-up resistor. This would also make sense since in the act of unplugging and plugging in the DAC would would have had mechanical force on the USB jack.
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post #1487 of 1560
1/9/09 at 10:22am
Quote:
Originally Posted by Richi View Post
Thanks for the tip about the hotfix. Sadly after installing this the problem still persists. Vista recognizes a device but labels it unknown in device manager. I have been through all connections again and checked my work and it all looks ok. Does this problem sound familiar to anybody and would you most likely put this down to a driver/OS problem or could it be a problem with the build of the dac?

Cheers.
Rich
Sorry to say - I have two laptops and a PC running Vista. They never give any hesitation about recognizing an AlienDAC or a BantamDAC.
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post #1488 of 1560
1/9/09 at 11:58am
Quote:
Originally Posted by Richi View Post
Does this problem sound familiar to anybody and would you most likely put this down to a driver/OS problem or could it be a problem with the build of the dac?

Cheers.
Rich
I had this issue with my first Alien build. It turned out I had a solder bridge that I had missed under one of the caps - all your voltages are correct adn there are no bridges between the dac chip legs?

I went over every passive component on the board with my meter, checking each for 0-ish ohms. Lo and behold a hidden bridge under one...
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post #1489 of 1560
1/9/09 at 1:00pm

Thanks!!

Thanks everybody and thanks Wiatrob, I did a thorough inspection of the capacitors and found a short beneath c12. I've fixed that and now windows recognizes the pcm2702! Great.

Sadly I'm not there yet because I only have audio from my left channel. Looking at the schematic it doesn't look like there is much going off from the output of the dac, just one resistor to ground and CR. CL and CR both test good.

Sorry for all the questions but I'm getting there. Any ideas what can cause this mono signal?

Rich
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post #1490 of 1560
1/9/09 at 2:54pm
A little more info on my one channel problem:

I get 2.35v at the OUTL pin and only 0.08v at the OUTR pin. All the components that appear to be related to the right (faulty) channel, C19 and L18, appear to be connected ok and I get the full 4.7v here.

I'm new to all this but I can't help but think that maybe the PCM2702 is damaged on the right channel. From what I have seen the chip has separate DAC sections for each channel so could this be the problem?

It's a shame cos the left channel sounds dead nice!

Anyway, enough of this for today.
Thanks again.
Rich
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post #1491 of 1560
1/9/09 at 3:09pm
Quote:
Originally Posted by Richi View Post
A little more info on my one channel problem:

I get 2.35v at the OUTL pin and only 0.08v at the OUTR pin. All the components that appear to be related to the right (faulty) channel, C19 and L18, appear to be connected ok and I get the full 4.7v here.

I'm new to all this but I can't help but think that maybe the PCM2702 is damaged on the right channel. From what I have seen the chip has separate DAC sections for each channel so could this be the problem?

It's a shame cos the left channel sounds dead nice!

Anyway, enough of this for today.
Thanks again.
Rich
So sorry to agree with you, but I've fried a few Alien DACs and the symptoms are just as you describe - one channel loses voltage. Several of us agree that the most likely cause is back-offset in an amp's input connectors (measured on the SSMH) or tiny arcing when connecting to the input of a live amp.

The only thing that protects the output of the DAC chip itself are the CL and CR coupling capacitors. If they are not fully charged, the DAC chip is completely unprotected. A good practice is to make certain the CL and CR connections are robust and reliable, and that you connect the DAC to USB power a few minutes before connecting it to an amp. This will ensure those capacitors are fully charged and blocking DC spikes that might hit the PCM chip. I typically leave my DACs connected to the PC all the time, so they're always well charged before I ever turn a headphone amp on.

P.S. Note that the resistors to ground at the coupling caps are 330K - this is a relatively high value for loading coupling caps, probably intended to prevent putting undo current load on a PC's USB line (which can prevent recognition by the OS). However, it means that even for the very small coupling caps used by the Alien (or the BantamDAC), it still takes awhile to charge them.
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post #1492 of 1560
1/9/09 at 3:40pm
Oh Dear! Sounds like I'll have to build another one. It's a shame the exchange rate isn't what it used to be for us Brits. Man I wish I knew that bit of info before I plugged it in. I have an old amp, a NAD 3020 so I bet this was the cause.
Thanks for the help.
Rich and his mono Alien DAC.
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post #1493 of 1560
1/22/09 at 8:23am

Success

I just wanted to thanks to the guys who replied to my earlier questions. I got my new kit from Jeff yesterday and its up and running right now. Looks like I did indeed damage the Dac chip on my first attempt. Anyway this one works great and the soldering is much improved from my first effort. All in all a great little project. Time to look for what I can build next.
Thanks again.
Rich
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post #1494 of 1560
2/1/09 at 3:15pm
Hello

I just finished my second Alien Dac and im in the process of breaking in the caps. I always wanted to try the 47uF 6.3V NX-HiQ Black Gates as coupling caps, as suggested in the beginning of this thread.
My problem is that after 90 hours of continous break-in the dac still has almost no bass whatsoever. I really want to know if there will be a certain point where the bass will kick in.
I heard that the sound signature changes quite a lot within the first 100 hours, but the way i hear it nothing changed in the bass department

My idea was to switch to 4,7 uF Sonicaps Gen I´s if the bass doesn´t improve. Any expierence with these?

Thanx
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post #1495 of 1560
2/1/09 at 3:18pm
Quote:
Originally Posted by refuzoid View Post
Hello

I just finshed my second Alien Dac and im in the process of breaking in the caps. I always wanted to try the 47uF 6.3V NX-HiQ Black Gates as coupling caps, as suggested in the beginning of this thread.
My problem is that after 90 hours of continous break-in the dac still has almost no bass whatsoever. I really want to know if there will be a certain point where the bass will kick in.
I heard that the sound singature changes quite a lot within the first 100 hours, but the way i hear it nothing changed in the bass department

My idea was to switch to 4,7 uF Soniccraft Gen I´s if the bass doesn´t improve. Any expierence with these?

Thanx
Although it's true it takes this long or longer for the bigger Black Gate NX's, I have not experienced it taking anywhere near this long with BG's on the Alien - more like overnight, or something similar. Even then, it's a question of smoothness and detail, not lack of bass (on the small ones).

I'm wondering if perhaps you have the output connector wired up incorrectly? That can sometimes be mis-interpreted as a lack of bass.
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post #1496 of 1560
2/1/09 at 6:38pm
I have 4.7uf NX-HiQ caps on my Alien and Gamma 1 DAC's. They took at least 100 hours to fully break in, but as Tomb said they were harsh and shrill at first, not lacking bass.
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post #1497 of 1560
2/1/09 at 11:13pm
Thanks for the quick reply.

Quote:
I'm wondering if perhaps you have the output connector wired up incorrectly?
I dont think so, but the wiring between RCA Jacks and the pcb is a litte long (3cm) and creates a loop inside the case (covering some caps). But then again I dont see how this could affect the bass. Perhaps 47uF is somewhat oversized and takes longer to be broken in?!?

How exactly could the wiring be incorrect without creating lots of static or buzzing sounds?

Perhaps it would help if I´d use different values on the R15 R16 resistors? They form a highpass filter together with CL/CR, right?

I want to emphasize that just the bass is affected. For instance in a song that has an exaggerated bassdrum the bass that should be a punch is only a slight flat knock.

Sorry i really dont see how i can improve the bass here.
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post #1498 of 1560
2/2/09 at 4:09am
Quote:
Originally Posted by refuzoid View Post
Thanks for the quick reply.


I dont think so, but the wiring between RCA Jacks and the pcb is a litte long (3cm) and creates a loop inside the case (covering some caps). But then again I dont see how this could affect the bass. Perhaps 47uF is somewhat oversized and takes longer to be broken in?!?

How exactly could the wiring be incorrect without creating lots of static or buzzing sounds?

Perhaps it would help if I´d use different values on the R15 R16 resistors? They form a highpass filter together with CL/CR, right?

I want to emphasize that just the bass is affected. For instance in a song that has an exaggerated bassdrum the bass that should be a punch is only a slight flat knock.

Sorry i really dont see how i can improve the bass here.
No - all I've ever used are 47uf, that's the best quality/size option if you're using Black Gate NX's. I'd say a high number - if not the great majority - of Alien DACs have been built with the BG NX's, so it would easily be a recurring issue if the BG's were at fault - but it's not and they're not.

If you lose the ground wire completely on the output connector, it can cause buzzing. However, if you swap the ground with one of the channels, it can cause a phase imbalance that will cause a loss of bass. It may even sound more "airy" because it's similar to what a crossfeed filter will do, and some people like the effect in small doses. However, bass is usually non-localized and depends on the combination of stereo channels to provide the most impact.

Again, it's just a guess, but long wire leads and loops can easily lead to a bit of confusion and transposing the connection.
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post #1499 of 1560
2/2/09 at 9:16am
I just had a thought this morning - you wouldn't be attempting to connect your AlienDAC directly to a pair of headphones, would you?

If so, stop right now.
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post #1500 of 1560
2/2/09 at 10:48am
Quote:
I just had a thought this morning - you wouldn't be attempting to connect your AlienDAC directly to a pair of headphones, would you?
No thats clearly not the case

I just checked the wiring and everything seems to be in order. So i guess I am back to square one
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