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Old 31st January 2012, 09:04 AM   #1991
hege is offline hege  Finland
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Quote:
Originally Posted by agdr View Post
Yeah that works great here.

PS. I've been switching headphones a lot and now my jack is loosing up a bit, so tightness is not that much of an issue anymore.
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Old 31st January 2012, 11:35 AM   #1992
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Found it!!! I desoldered R2, D6, D1, D5, and the gain switch but couldn't find anything wrong. All the joints looked visibly good. (Not any more...)

I was following the trace around looking for anything, when I noticed that a joint for the big cap on the side of board nearest D4 was just touching the trace running to the gain switch. The solder mask there is a little bit scratched. I removed some solder from the joint and the short is now gone.

Listening at the moment. The amp has passed all the voltage tests on NwAvGuy's blog. Only defect I can notice at the moment is channel imbalance at the very bottom of the volume pot.

Do you think it's most likely that I scratched the PCB, or that I killed the solder mask with heat? How hot is too hot? Do I need to keep my iron below 350 C? Is there anything that can repair these little trace scratches?

@nezblue: I understand your frustration at us beginners. I did edit my post almost immediately after posting though, as soon as I saw that I was wrong. I always expected it to be my fault but was baffled momentarily by the different pin layout on U5, U6. I know that people come and ask silly questions, but I'm willing to put in the work to learn and know better, eventually.

@agdr: Many thanks for your help - I was going to have a hard time finding this error. Hopefully I didn't make more in there!

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Originally Posted by nezbleu View Post
I am not trying to be a jerk, but I get frustrated when people keep trying to blame everything but their workmanship despite all contrary evidence. The PCB is fine, the circuit works as advertised, you made a short somewhere.
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Old 31st January 2012, 12:16 PM   #1993
agdr is offline agdr  United States
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Quote:
Originally Posted by SEdwards View Post
Listening at the moment. The amp has passed all the voltage tests on NwAvGuy's blog. Only defect I can notice at the moment is channel imbalance at the very bottom of the volume pot.
Hey congratulations on the working amp! You probably meant "power switch" instead of "gain switch". Yep that trace is the one going from that shorted node to the power switch and that joint with C3 is ground. The capacitor lead gets grounded on the top of the board via a through-hole.

Imbalance at the very low end of the pot is actually normal. Analog pots are only accurate to 20%, even the good ones like this Alps pot. That innacuracy really shows up on the low end. To do better you would have to go to a stepped attenuator which is pricey and the size of a golf ball.

The scratches on your traces and soldermask won't hurt anything and won't affect the sound. The biggest problem there, like you say, is allowing solder to stick to traces in places where it shouldn't.

Hey one more thing. Your D5 might be shorted. With batteries out and power adaptor unplugged try testing it with the DMM diode test function in both directions and compare to tests on D1. Thinking about your previous measurements that 106 ohms you got on the output of U6 was probably measuring what was left of D5. When the anode of D5 got shorted that would have pulled short circuit current through U6 and D5. U6 is short circuit protected, but not so much for D5.

Last edited by agdr; 31st January 2012 at 12:46 PM.
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Old 31st January 2012, 04:44 PM   #1994
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Continued tech support, great service.

I see voltage drops of ~166 mV for both D1 and D5. (More like ~145 mV for D6 and D2). Safe ranges? Looks like I may have dodge a bullet?

RE: the volume. Since I'm running from a Xonar D1 in 24 bit mode, I'm probably better off lowering the volume a little at the PC side than using the pot below 9 o'clock or so, I suppose. Better to lose something in the digital regime where I have some headroom. I'm using Fostex T50RPs and can't handle full volume from the PC + O2 with the pot near 12 o'clock.

Quote:
Originally Posted by agdr View Post
Hey one more thing. Your D5 might be shorted. With batteries out and power adaptor unplugged try testing it with the DMM diode test function in both directions and compare to tests on D1. Thinking about your previous measurements that 106 ohms you got on the output of U6 was probably measuring what was left of D5. When the anode of D5 got shorted that would have pulled short circuit current through U6 and D5. U6 is short circuit protected, but not so much for D5.
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Old 31st January 2012, 04:58 PM   #1995
agdr is offline agdr  United States
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Quote:
Originally Posted by SEdwards View Post
Continued tech support, great service.

I see voltage drops of ~166 mV for both D1 and D5. (More like ~145 mV for D6 and D2). Safe ranges? Looks like I may have dodge a bullet?
Yep those look good, given that they are Schottky diodes.

I agree, you would probably have better luck with channel equality controlling the volume on the digital side. If you made your O2 with the standard 2.5x and 6x gains you might want to consider changing the resistors and backing that down to 1x and 2.5x. That is what I'm running my O2s at. The higher gain pair apparently is most useful for some portable players with 0.5Vrms outputs.
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Old 31st January 2012, 05:03 PM   #1996
Alexium is offline Alexium  Ukraine
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I haven't been around for like a month, what's new? How's progress on ODAC?
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Old 1st February 2012, 12:00 PM   #1997
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Last word that I can find from NWAVGuy in response to " Could you give a rough estimate of when we might see the ODA/ODAC for sale? Thanks in advance!":

"...the plan is to release the design before the end of March. That's only a goal, no promises. It will take at least a few weeks beyond the documentation release before there are completed boards/amps for sale. But it should be well before summer."
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Old 1st February 2012, 12:18 PM   #1998
Alexium is offline Alexium  Ukraine
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FloridaBear, thanks.
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Old 1st February 2012, 11:48 PM   #1999
nezbleu is offline nezbleu  Canada
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Quote:
Originally Posted by SEdwards View Post
Found it!!! ...
Listening at the moment. The amp has passed all the voltage tests on NwAvGuy's blog.
I am genuinely glad that you found the problem and fixed it, and that you have a working amp. I am also sorry that I was a bit grumpy the other night. We are all here to help, and I dare say most of us here have benefited from help freely offered by others on this forum. I know I have. If it helps I really just wanted to get you looking in the right direction and not distracted by red herrings.

Good catch, by the way, finding that solder bridge, those can be very difficult to locate.
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Old 2nd February 2012, 04:56 AM   #2000
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Finally got my kit and have it working. and post 2000
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