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Circuit error in Lite DAC-AH: Easy fix - Page 10

post #136 of 213
Anyone els notice that this DAC still fails the udial clipping test even after correction R35/36
post #137 of 213
Quote:
Originally Posted by regal
Anyone els notice that this DAC still fails the udial clipping test even after correction R35/36
I play it fine. Btw, i have my Vref set to 3.995v
post #138 of 213
Thread Starter 
Quote:
Originally Posted by fe3836
I gave the pointer to PV; their response was they couldn't fix it because Li Te didn't admit there was a problem
I bought my second DAC-AH from www.diykits.com.hk and was told that even though Lite was told about the problem, they still wouldn't fix it. They must have a lot of 270 ohm resistors in inventory. Doesn't make since to me. The good news is that diykits changed the resisters to 150 ohms before they shipped my unit. I thought that was really nice. I don't know if they're doing that on all of them or if you have to ask for it.
post #139 of 213
Thread Starter 
Quote:
Originally Posted by _Rand_
Thats just the thing, I can't get mine lower than about 3.85v.

Not sure why unless I somehow damaged the pot.

Almost forgot, I somehow managed to rip the LED wires off the board, where the hell were those soldered on? Its not a big deal really, but I would prefer that it work.

EDIT: measuring from signal pin to ground I get about 3.3-3.4mv (measure on the 200m setting) on the left channel and about 3.7 on the right.
The LED wires go to the terminals of capacitor C27, which is the 5V supply. On mine the striped wire goes to the positive side of C27 and the plain wire goes to ground.

I'm sorry you're having so much trouble. One thing I want to mention is that I inadvertently drilled out some of the through-holes on the printed circuit board to make it easier to install new components, but then I realized that wasn't a good idea. This board has through-hole plating which is necessary to make connections from the top of the board to the bottom. I may have drilled away this through-hole plating and broke the connections. I ended up soldering on the top and bottom just to be safe.

I have no idea if you've done the same thing, but if you did, that could be the problem. Try soldering on both sides of the board wherever you've messed with it.

Also, it's hard to believe that the trimpot is bad, although I guess it could be. It's much more likely that the problem is in the area of the resistors.
post #140 of 213
Hi Kim,
You know i got so caught up with my last post and getting all the pics in order that i forgot to thank you for all your help. You answered all of my stupid questions and without your help i wouldnt be having sonic orgasms when i listen to my favorite albums. Thanks again.
post #141 of 213
Thread Starter 
I'm glad I could help. I got some ideas from you and others in this forum too. I'm also very pleased with this DAC, especially after the mods. It's fun when you make some changes and can actually hear improvement. Even without any mods (except the resistor change) the DAC-AH is a great DAC.
post #142 of 213
Hi all,
My dac ah came in yesterday from Eddie, and it had the wrong resistors (270 ohms) with 6 volt supply. So, I changed them to 148 ohms. Being an anal enginerer, I double checked Kim's calculations, and 3.3V is dead on but I'd maybe go for 141 ohms in the long term, to be safe at the edge of the spec, but 148 provides adequate margin.

I also warmed it up and tweaked the bias to 3.3V. Thanks for the warning Kim, the bias drifted about 0.2V down during warm up.

Unfortunately, the sound was really bizarre. The low end was ultra "fluffy" and exagerated and on big bass transients would tend to splay across left and right. Even the high end, when called to be dynamic, would tend to splatter a bit.

Anyone else hear this with their dac ah and find teh cause? I hope this doesn't entail having to hunt for issues on the board, and I'm not sure I'm up to mailing this back to Hong Kong.

Thanks, Dave
post #143 of 213
Thread Starter 
Dave,

Did you listen to the DAC before your mod? Is the weird sound only after the mod?

It sounds from your description like the problem is in both channels. Can you confirm this?

If you've got the right resistors and bias voltage it's hard to imagine what's wrong. As I suggested recently, try soldering the resistors on the top and bottom of the board. Be careful not to touch the capacitors. My only other suggestion is to remeasure the 6V to the DACs.
post #144 of 213
Hi Kim,
Thanks for writing. Verified resistance, soldered to only one side of the board but measured impedance from Ic to connector ground (so pads are OK), and checked 6V.

Its really odd. If I had to guess, it sounds like there's little to no psu capacitance, so I may need to hunt for cold solder joints. I'll also play some dynamic signals (bursts) and monitor the psu rails with an ac meter.

This weekend when I get some spare time, I'll run power spectrums with sines cut on CD (my PC card doesn't support didgi out: Juli@ on the way to fix that!).

Bit of a drag, but if it takes much time I'll pitch it and buy something else. Time is short these days.

Thanks,
Dave
post #145 of 213
Quote:
Originally Posted by DDF

Unfortunately, the sound was really bizarre. The low end was ultra "fluffy" and exagerated and on big bass transients would tend to splay across left and right. Even the high end, when called to be dynamic, would tend to splatter a bit.

Anyone else hear this with their dac ah and find teh cause? I hope this doesn't entail having to hunt for issues on the board, and I'm not sure I'm up to mailing this back to Hong Kong.

Thanks, Dave
Sorry to hear that, but no, even before the I/V resistor mod and the output coupling capacitors mod my stock DAC-AH didn't have the problem you described above. I did, however, allow it to be burnt in (unattended) for over 60 hours before I started my listening sessions.
post #146 of 213
Thread Starter 
Quote:
Originally Posted by DDF
Hi Kim,
Thanks for writing. Verified resistance, soldered to only one side of the board but measured impedance from Ic to connector ground (so pads are OK), and checked 6V.
The pads and traces are probably OK, but I noticed that the through-holes are also used to make connection from the resistors to the opamps and from DAC to DAC. It's definitely a long shot, but I still suggest soldering on both sides any connection that you've messed with..

I'm still curious if you listened before the mod. If you didn't then I guess we don't know if the problem is due to the mod or not.

Unfortunately, one of the problems with buying from Hong Kong is the return shipping if you have a defective unit. I'm assuming that you would have to pay return shipping. I guess I've been lucky. Both of the units I received were fine.
post #147 of 213
Quote:
Originally Posted by Kim Hardee
I'm still curious if you listened before the mod. If you didn't then I guess we don't know if the problem is due to the mod or not.
Sorry, forgot to mention. No, I didn't, it went straight onto the soldering bench. It'd be trivial to change it back, but I'm certain my mods are clean. I'll pull the pcba and check the back side for cold solder joints etc.

In the last 2 months of ordering on-line:
- Go-vibe : all thumbs up
- DT250-250's: connector broke in 3 days
- K81DJs: merchant didn't send and now I'm in the arbitration process
- Fluffy the dac.

Looks like I'm a .250 hitter. Canada post loves me though!

Dave
post #148 of 213
What type of caps did you use in the bypass. When I first installed my NOS vitamin q caps, the bass was real sloppy and fuzzy, but that went away with burn in. It sounds like you have a lot of experience with electronics, so this might be obvious to you.
post #149 of 213
Quote:
Originally Posted by izquierdaste
What type of caps did you use in the bypass. When I first installed my NOS vitamin q caps, the bass was real sloppy and fuzzy, but that went away with burn in. It sounds like you have a lot of experience with electronics, so this might be obvious to you.
Hi,
No cap changes yet, but that's all coming. Still, what I'm hearing shouldn't occur due to component quality, it sounds (literally) like a board issue. If I track it down I'll post the findings in this thread.

I've designed audio boards so this shouldn't be too big a deal, its just time.
post #150 of 213
Quote:
Originally Posted by izquierdaste
What type of caps did you use in the bypass. When I first installed my NOS vitamin q caps, the bass was real sloppy and fuzzy, but that went away with burn in. It sounds like you have a lot of experience with electronics, so this might be obvious to you.
I noticed the same thing with my surplus paper in oil caps, I thought something was wrong but it cleared up in less than an hour.
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