E-MU 0404 usb 2.0 and some "artifacts peaks" on left channel - Page 2 - diyAudio
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Old 26th October 2012, 07:03 PM   #11
iko is offline iko  Canada
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There's a thread or wiki on this site in which I tried to identify the on-board chips. There were quite a few dc-dc converters to provide various positive and negative rail voltages, all running at various kHz speeds.

Edit: found it. http://www.diyaudio.com/wiki/E-MU_0404_USB_mod_wiki
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Old 26th October 2012, 11:50 PM   #12
sidiy is offline sidiy  Canada
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Thanks Ikoflexer,
Starting from that thread I did some homework and found these links of interest:
Inside view
Loopback tests

I also opened my unit and I think I found the problem. They announced some rain in Montreal this week-end... so stay tuned. I will post pictures and a step-by-step "how to"... if my fix works.

There are no door prizes but if anyone cares to take a guess...
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Old 27th October 2012, 06:38 PM   #13
iko is offline iko  Canada
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Bad caps?
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Old 27th October 2012, 09:03 PM   #14
qusp is offline qusp  Australia
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oh I dunno, the 12MHz crystal, plus what appears to be DGND and some DC->DC convertors in the second pic, folds over when closed and sits directly above the dac? in the pic with the boards folded out like a book it appears that section will sit directly above and VERY close
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Old 27th October 2012, 09:40 PM   #15
qusp is offline qusp  Australia
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wrong, its the DIR it sits above. with that 12MHz XO there clocking a logoc, FPGA, and the boards folding over like that, its a recipe for noise. I would test to see if you can get it to work with it folded open and just track it down
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Old 28th October 2012, 01:55 AM   #16
sidiy is offline sidiy  Canada
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Well, it worked... I have a bunch of photos, starting with a general view of the troubled area. I ruled out the DAC and output circuits since (luckily) these did not meet the conditions.
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File Type: jpg EMU.jpg (420.6 KB, 468 views)
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Old 28th October 2012, 02:42 AM   #17
sidiy is offline sidiy  Canada
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Next one shows a "textbook" example on how a differential pair should not be routed !

The ADC has a yellow dot where the AINL pins are. All is good up to the anti-glitch capacitor C101 which is not far, but after that the show is on...the traces go on different inner layers and cross each other and then come on top at R151 (from pin 4) and R167 (from pin 5).

The colors tell the rest of the story, a nice loop is formed (the green trace even changes layer, where dotted, near the top right sot23s). There is a DC-DC converter right above with an unshielded inductor, L6 and an FPGA that has to run data at USB rates (plenty of traces there parallel to our top trace).

On a brighter note the blue lines show the right channel pair routed on a inner layer and top layer. They're close togheter and far from dangers.

I guess waiting for a board revision is out of the question, since the 0404 is obsoleted
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File Type: jpg EMU_1.jpg (356.6 KB, 445 views)
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Old 28th October 2012, 03:21 AM   #18
sidiy is offline sidiy  Canada
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The fix is obvious.
1. Lift R151 and R167
2. Cut the traces near the pads of R123 and R128 as shown, making sure not to go too deep or to chip some neighboring components.
3. Solder a pair of wires, twisted a couple of times, to rework the connection. On the right side I chose the pads of R108 and R110 which belong to the same original nodes while for the left side I used the leftmost pads of R151 and R167. I did not want to pass the wires over the ADC to C101, not optimal in my opinion. Make sure not to reverse the phase.

Note: Photos are now turned upside down, makes easier to read component designators... sorry, my bad.
Attached Images
File Type: jpg EMU_2.jpg (339.4 KB, 404 views)
File Type: jpg EMU_3.jpg (634.8 KB, 385 views)
File Type: jpg EMU_4.jpg (415.3 KB, 427 views)
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Old 28th October 2012, 03:50 AM   #19
sidiy is offline sidiy  Canada
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I reassembled my EMU without any other touch-ups or upgrades. Apart from the mod shown my unit is still in "stock" form. As external supply I use a breadboarded LT3080 supplied with a 9V switching walwart.

Before showing the results I will post for reference some older tests. The photos are lower rez and cropped differently than the new ones. On top of that I don't recall the sample rates used but by their looks they're higher than 88.2k.
But it doesn't matter anyway - as you'll see later.

The left channel looks pretty busy...
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File Type: jpg Noise_before.jpg (130.3 KB, 300 views)
File Type: jpg THD_before.jpg (110.2 KB, 213 views)
File Type: jpg DR_before.jpg (41.5 KB, 201 views)
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Old 28th October 2012, 04:03 AM   #20
sidiy is offline sidiy  Canada
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And the results...
I saved the measurements only for 44.1k and 192k, but I checked all the rates and the results are pretty much identical - considering the corresponding measurement bandwiths for each case.
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File Type: jpg Noise_44k.jpg (107.0 KB, 268 views)
File Type: jpg Noise_192k.jpg (104.9 KB, 266 views)
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