my DAC design - pup1 DAC
Apr 11, 2012 at 8:09 AM Post #241 of 675

cobaltmute

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So as tomb has said, my new version prototype is working. And as tomb has said, I do think it sounds excellent. I am running the new version with a very nice pair of RCAs versus a 3.5mm mini to RCA cable with the old version, so it isn't a total apples to apples comparison. That being said, I do think, as a *system* including the cables, it sounds better than the first version.

However, I am trying to track down an offset problem with my build. It appears to be something specific with the op-amp as I've replaced many of the parts around it While the offset is higher than I would like on one channel, it is still in spec for what the maximum allowed for the chip. I'd ordered new chips late last week, that I should be able to get on Thursday. I've also ordered an alternative part that has better offset specs, at the trade-off of a bit less output drive.

So a little more patience and I think we'll be able to release the prototype board to you all very soon.

 
Apr 17, 2012 at 2:39 PM Post #243 of 675

c12mech

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I'm still listening to the first one and would be happy to prototype this version and offer a comparison.  The new layout looks like it should be a little more soldering friendly.  Are the pads longer for the dac chip this time.  I remember that being an issue with the first board.  I look forward to seeing how this one compares.
 
Apr 28, 2012 at 7:29 PM Post #245 of 675

tomb

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No, if you read the last several posts in the thread, there is an offset issue on cobaltmute's build.  I'm hoping to build one tomorrow - I've been backed up in orders with Beezar since doing my taxes, but I'm just about caught up.
wink.gif

 
Anyway, I guess if my build(s) confirm cobaltmute's findings, we may need to modify the layout a bit to reduce offset from the opamp.  So, hang loose and give us a chance.  We fully expect to let several of you prototype the PCB, but not until we have a better handle on this.
 
Keep in mind, cobaltmute has indicated that this version sounds even better than the first.  If you apply it to an amp that has input coupling caps, output coupling caps, or input/output transformers, there will be no issue at all.  However, we want it to work well with any amp.  So, there may be some changes with the PCB design ... or not.  We'll just have to see.
 
We will keep you updated.
smily_headphones1.gif

 
 
EDIT: For those of you who may not be familar with "offset", it's some remaining DC voltage that can be measured at the signal outputs of the pupDAC.  These readings are in the single-digit micro-Volts, but understand that as a source, it means those micro-Volts will get amplified when connected to an amp.  The result might be (might be) that the output at the amp will be an amount of DC voltage that could possibly - in the worst scenario - be a cause for concern.  We are working to get that down to a safe range.
 
May 4, 2012 at 10:52 PM Post #247 of 675

scootsit

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Quote:


I was just looking at this, and I could very well be wrong, but aren't the silkscreens on the top-side backwards at the output? Isn't the TRS, tip=left, ring=right, sleeve=ground? Here, it appears that left and right are switched. Again, I assume I've made a mistake, but I just thought I'd ask.
 
May 5, 2012 at 8:15 PM Post #250 of 675

Avro_Arrow

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I would take one of the boards that has some offset if you are just going to throw them
out anyway...the amp I'm prototyping now has a servo.
 
May 6, 2012 at 9:52 AM Post #251 of 675

cobaltmute

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I would take one of the boards that has some offset if you are just going to throw them
out anyway...the amp I'm prototyping now has a servo.


We are waiting for tomb to build his protos to see what they do before we offer anything. Even if tomb's has issues like mine,we will still offer them out (with a very large disclaimer about the offset).

The offset issue only seems to be affecting the left channel on my board. I've gone through 4 different op-amps and the right channel has been good but the left has been between passable and atrocious.

I'll admit to not having spent a lot of time with it the board over the last few weeks. I'm 4 weeks out from a triathlon and there is a bet with friends on it, so between trying to do normal stuff, training and recovery, I'm more than just a little tired. It's only the beginning of May and I've been on the bike for more distance this year than I rode all of 2011.
 
May 6, 2012 at 10:06 AM Post #252 of 675

Avro_Arrow

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Hey, if it's any consolation, my Chinese HiFiDIY PCM1793 DAC has about 20mV offset on one channel no matter
what op amp I put in the output filter.
 
Good luck in the triathlon!
 
May 19, 2012 at 1:00 AM Post #253 of 675

Mullet

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Looks like a cool project. I'm interested in doing a prototype when you're ready.
 
May 20, 2012 at 3:56 PM Post #255 of 675

Avro_Arrow

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I saw a peloton of riders coming through my area up by Lake Simcoe yesterday...I was wondering if one of them was cobaltmute...
 

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