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Old 9th June 2012, 08:24 PM   #521
mogliaa is offline mogliaa  United Kingdom
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Quote:
Originally Posted by pmillett View Post
AHA! That is entirely possible. That would explain all of the symptoms. It souds like the (-) output of the driver has popped, probably an internal short to a power rail. The (+) side must still be OK.

I would replace it and see if that fixes the problem.

Pete
Thanks Pete,
Orderer the spare parts already. I measured the soundcard input DC and was surprised there was an DC offset. I thought there was a blocking capacitor?
Cheers,
Ale
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Old 9th June 2012, 08:40 PM   #522
kevinkr is offline kevinkr  United States
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Check for shorts to the supply rails, etc., I had a problem with my board and it turned out to be an almost invisible short between ground plane and the negative rail. Shorts to other places are possible. It took an 8X loupe to see it. Mine has worked fine since I found the problem - more than a year now.
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Old 11th June 2012, 02:39 AM   #523
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Originally Posted by mogliaa View Post
Thanks Pete,
I measured the soundcard input DC and was surprised there was an DC offset. I thought there was a blocking capacitor?
Cheers,
Ale
There should be no DC offset. Measure it unplugged from the soundcard. Does the LCD meter read 0? If so the output driver (U8) may be damaged.

Follow the signal back... there should be 0V DC on the outputs of U4, the output of U7, also the output of U8. Assuming +/15V are OK, there must be another damaged component causing the offset. Maybe the protection diodes in the front end?

Pete
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Old 11th June 2012, 06:19 PM   #524
mogliaa is offline mogliaa  United Kingdom
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Here is the summary of the first repair of Pete's interface
After checking all voltages without ICs it seemed ok to try following test input signal and adding each IC for every stage. Started with U4, then U7 and finally U8. All had to be replaced...
Lesson learned: label your soundcard cables so you don't make this stupid mistake.

Attached is a loopback test with the soundcard

Thanks for the help
Cheers,
Ale
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File Type: jpg loopback test 1kHz 1 Vrms.jpg (190.5 KB, 467 views)
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Old 8th July 2012, 09:54 PM   #525
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Question Odd Frequency Response / Increase SCI Output Vrms

Just tried assembled Sound Card Interface (further referred as SCI), with ESI Juli & ARTA, and have some oddities/question(s):

1) Frequency response is not flat (look at the graph attached). I'm sure I did something wrong, but where to look for possible bugs at first? Voltage from sound card is OK (I meant the same at all frequencies). Mode is 192KHz/24 bit, displayed by ESI monitor, FFT window in ARTA 65k.

2) ESI Juli works fine with up to 2.8V input voltage, 0.5V from SCI is a way too low. Is it possible to increase output voltage from SCI to "sound card in" to about 2 - 2.5V RMS without degrading precision of THD measurement.

3) The best precision so far I've got with SCI is 0.033%, with INPUT/GEN OUT both connected to 33K resistor. IMHO this is somehow relate to problem #1.

Thanks in advance for any suggestion(s).
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File Type: jpg PMillettSCI-FR.jpg (104.0 KB, 423 views)
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Old 8th July 2012, 11:18 PM   #526
Pano is offline Pano  United States
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A 5dB shelf? That's odd. Do you see the same thing at other sample rates?
The soundcard loop-back does not do this, right?
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Old 9th July 2012, 07:05 AM   #527
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A 5dB shelf? That's odd. Do you see the same thing at other sample rates?
The soundcard loop-back does not do this, right?
Yes, it is independent of sample rate.
Sound card is fine, I connected sound card input and output together and verified.
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Old 27th July 2012, 05:17 PM   #528
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I just ordered Pete's PCB for this soundcard interface. I am looking forward to this build.

Using his parts list, I have order all of my parts. Most from Mouser. Some from Digikey. But all components were in stock.

On Pete's list he is using Yaego Metal Film Resisters. Under comments he states "MF only, generic ok".

Question: I substituted Xicon MF-RC Series resisters from Mouser. Any problems with this substitution? Links to both datasheets below.

Next question: Looking at Metal Film Resister Datasheets from various manufactures I notice that some resisters are available in 0.1 tolerance and lower noise series. Of course at a higher cost. Would it make any difference in the noise floor spending a little extra on lower noise series resister?

A lot of the post here are over my head but I am learning. I have read throught this post at least two times. I think I am ready. However, I hope I can get support when needed.

Thanks,

Dennis

http://www.mouser.com/catalog/specsheets/XC-600046.pdf (I used this one)

http://www.yageo.com/documents/recent/Leaded-R_MFR_2011.pdf (He listed this one)
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Old 30th July 2012, 01:52 AM   #529
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I have been searching for the best USB/Firewire Soundcard to use with my new soon to be built interface. I will be using a laptop which has both usb and firewire. My budget is around $200. I would like it to have balanced inputs as well as ouputs to match Pete's interface inputs and outputs. I would also like 24bit/192khz device.

The one I have been looking at is M-Audio ProFire 610. Any concerns using firewire over usb?

Any other recommendations?
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Old 30th July 2012, 05:38 PM   #530
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I use the Profire 610. Fantastic measurements; very low noise floor and low distortion on the input. I use channel 3/4, as it is direct to the A/D. Definitely not as good when using channels 1/2. Drivers for win7 are pretty unstable in my opinion; I find myself having to uninstall and reinstall them any time you power it down wrong or hiccup the measurement. There is also a history of these interfaces failing entirely when you attempt to hot swap (something FW is supposed to be capable of).

For future use, I would suggest USB, as FW is nearly dead. Both mac and win laptops do not provide FW anymore (we'll see what success Thunderbolt to FW has). I had to spend way too much on a cheaply built clunky Lenovo ($2200) just to find a laptop with FW, and this model was soon to be obsoleted. I'm of the laptop preference; will never own a desktop again (except the Mac Mini as a file server).

So when it works, it's one of the best, but it is tempermental and FW's future is questionable.
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