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The Holy Grail - Page 15

post #211 of 232
What is coming out of your DC/Dc converter?
post #212 of 232
8.4v across C23, I have 620k instead of 634k in R6 because it was all I could get.
post #213 of 232
Thread Starter 
Quote:
Originally Posted by Magsy View Post
Seem to have a little problem with my REG101. I checked the output and it was the same as the input, 4.75v. I replaced it with a fresh one and it is the same.

What could be causing the regulator to seemingly not regulate? I've reflowed all the joints but they look ok, all of the 3.3v pins on the pcm2707 read 4.75v
I think there must be a bridge somewhere. Between C7 and C8 is the obvious spot, but it could be elsewhere too. Can you post high res pics of the top and bottom of the board

Quote:
Edit: I even read 4.75v across C8 with no Reg101 in place, the DAC also works without Reg101 installed!?! :|
Not surprising, but also not ideal. You can run this on a higher voltage, but if you do this and leave in L6 and L10 you may be in danger of damaging the 2706. 4.75 is right on the edge of where it will work -- any higher and it will probably stop, and long term stability is unknown.
post #214 of 232
Thanks, appreciate the help.

This is the best I can do with the cameras I have here. I agree it seems very much like it's bridged somewhere, I'll check it out again. The PCm does get warm quite quickly and there is distortion if I turn up the volume in windows, if I turn it down it sounds fine..

http://magsy.net/headfi/hpdac/topdown.jpg
http://magsy.net/headfi/hpdac/angle.jpg
http://magsy.net/headfi/hpdac/back.jpg
http://magsy.net/headfi/hpdac/pcmcloseup.jpg
post #215 of 232
Thread Starter 
Do you measure continuity between C7 and C8?
post #216 of 232
Thread Starter 
Also, look at the ground pin of VR3. It looks like there might be a small bridge there.
post #217 of 232
Yes, the inner of C7+8 have continuity, no resistance.
post #218 of 232
Thread Starter 
Quote:
Originally Posted by Magsy View Post
Yes, the inner of C7+8 have continuity, no resistance.
So there is definitly a short somewhere ... now you just have to find it. Fortunately, the amount of copper that should be continuous with C7 is small, so looking along it should yield an answer. The parts that are conneted directly to this buss are C7, L7, VR3, DC1, C24, L2, the USB Jack, and RLED.

Around L7 and L8 might be a good place to check, too.
post #219 of 232
Stupid question, C7+8, I have to remove the caps to test continuity ? Ive tested with them in but they are both connected to ground..
post #220 of 232
Thread Starter 
Quote:
Originally Posted by Magsy View Post
Stupid question, C7+8, I have to remove the caps to test continuity ? Ive tested with them in but they are both connected to ground..
No. The caps block DC which defines continuity. You may get a short burst of continuity while the caps charge, but then they will block it. If you have an extra cap laying around, try measuring continuity across the leads to see this happen.
post #221 of 232
Quote:
Originally Posted by dsavitsk View Post
No. The caps block DC which defines continuity. You may get a short burst of continuity while the caps charge, but then they will block it. If you have an extra cap laying around, try measuring continuity across the leads to see this happen.
Argh, http://magsy.net/headfi/hpdac/back.jpg

I had the two ferrites mounted wrong, I blame the lack of silkscreen

Sorry! I feel like an arse, I've spent hours fiddling with this and made some things a little messy by resoldering, removing and replacing so much. I've been through 2 Reg101's, 2 DC-DC convertors, a few ferrites and caps. Kinda angry but happy also

It works fine now, although now that reg works I get the 'too much power' message off my Apple keyboard but it works direct.

One problems still persists though and that is distortion unless the volume in windows is -10db (foobar) With volume lowered it works fine right up to ear bleeding levels via the pot. Anyone else had this? I have had this problem with my Guzzler DAC for a very long time, I assumed something had gone wrong but I couldn't be arsed to open the case up. (The Emu 0404 in the same PC is fine.)
post #222 of 232
Thread Starter 
Quote:
Originally Posted by Magsy View Post
One problems still persists though and that is distortion unless the volume in windows is -10db (foobar) With volume lowered it works fine right up to ear bleeding levels via the pot. Anyone else had this? I have had this problem with my Guzzler DAC for a very long time, I assumed something had gone wrong but I couldn't be arsed to open the case up. (The Emu 0404 in the same PC is fine.)
What resistor do you have for vref and the i/v? I'm no good at reading the stripes, but vref is different which could account for something?
post #223 of 232
I have resistors for 8v and I'm running 5v atm, so it could be that?

I have 2 x 2k7 and 1 x 1k5 in there.
post #224 of 232
For some reason I decided to swap out the 2707 instead of playing with i/v resistors first....big mistake. I stuck the replacement 2707 on the wrong way around and then lost my temper removing it, taking all the dummy pads with it.

In short, 3x1k in I/V work fine, with no distortion.
post #225 of 232
I bumped up the TDA up to 8v and it sounds quite good there, I also increase the stepup to 10v to allow for my less than 'low' dropout regulator.

Is there an easy place to tap in and provide external power? I think if I could cut +ve after RLED (on schematic) so usb powers HOST and the rest is supplied by external, it would work. I want it to be switchable though...like the Guzzler DAC.

Easiest is just to pull +ve from the usb cable, but I'm not sure the device will work if I leave that float and provide +5v there?
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