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Old 30th July 2012, 09:29 PM   #531
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Hey thanks for a candid and honest answer Zigzagflux.

I get cross eyed looking at all the specifications from one board to another. I thought the same thing about firewire v.s. usb. But I thought the specs were better on the this unit than the other usb units.
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Old 5th August 2012, 12:45 PM   #532
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I received my PCB and all the components to stuff the board. I am about half way done and should finish it today.


If I understand Pete's interface correctly, the input & output on the interface is balanced. Can a sound card with just unbalanced RCA in & out be used with Pete's interface? Or will it only work with sound cards that have balanced in & out.


I am still looking for the best External sound card to use. Most of the recommendations on this thread are over 2 years old (M-Audio & ESI, and E-MU). It seems to me that technology has changed in 2 years. I have a target budget around $300. Then again, maybe I am chasing my tail.
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Old 5th August 2012, 07:02 PM   #533
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Quote:
Originally Posted by dennismiller55 View Post
I am still looking for the best External sound card to use. Most of the recommendations on this thread are over 2 years old (M-Audio & ESI, and E-MU). It seems to me that technology has changed in 2 years. I have a target budget around $300. Then again, maybe I am chasing my tail.
I have ESI Juli and I can say this is one of the best sound cards for the buck. It has both balanced and unbalanced (RCA) inputs / outputs.

However, I'm still have mysterious problem with sound card interface (connected via balanced) to ESI Juli, and ARTA spectrum analyzer.

1) ESI Juli works fine, this is sure for 99%, if input and output connected together, THD is below 0.01% at any signal level.

2) The culprit seems to be the buffer between sound card out and DUT (device under test) input. If output voltage from SCI (GEN OUT) approaches 0.8V RMS, THD increases to as much as 1.5%. If output voltage from SCI (GEN OUT) is 0.5V or below, THD is about 0.15%, 10 times above normal level.

If anyone has any idea what's wrong, please advice. Thanks in advance.
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Old 6th August 2012, 10:10 AM   #534
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Quote:
Originally Posted by dennismiller55 View Post
If I understand Pete's interface correctly, the input & output on the interface is balanced. Can a sound card with just unbalanced RCA in & out be used with Pete's interface? Or will it only work with sound cards that have balanced in & out.
Sure... just connect the tip of the 1/4" jack to the center contact of the RCA connector, and connect ring and sleeve together to the outer contact of the RCA.

Pete
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Old 6th August 2012, 01:15 PM   #535
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Thanks Pete for the answer to my Balanced and Unbalanced input/outputs question. Simple enough.

I have completed stuffing the board. I am getting ready to mount the board in the case this morning. Several post have talk about grounding the Switch shaft. On the switch shaft I plan on using a thin washer with a ground wire attached with solder. Where is the best place to attach the ground wire on the pcb with the shortest run?
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Old 6th August 2012, 03:10 PM   #536
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In reference to my post directly above.

Looking at the schematic, SW4A Pin "A" is always at ground. Why could I not run a jumper fron the switch shaft right to Pin "A". Would this work?
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File Type: jpg DSCN5292-A.jpg (756.5 KB, 319 views)
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Old 8th August 2012, 09:57 PM   #537
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I have completed my Sound Card Interface. I installed shielding as discussed in various post.

The first time I powered it up I new something was wrong. Took me a long time but I discovered that I installed U1 Op Amp backwards. With U1 installed correctly, I was able to calibrate the meter section.

Then I ran back to back loop test first on the usb sound card, and then with the interface and sound card.

I have never used any of the FFT spectrum analyzer software programs talked about here. So this is new to me. After player around with serveral FFT software programs, I settled on ARTA for the test.

I am going to buy a better sound card but for the time being I am using what I have. A Creative Labs X-Fi External USB Card.

The first picture is: Loop back test of just the sound card.

The second picture is: Loop back test of both the sound card and the interface.

I thought the THD on just the sound card was not bad. But the THD of both is horrible.

Do you suppose I damaged U1 or some other component?
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File Type: jpg Arta SB Loop Back THD.jpg (156.1 KB, 293 views)
File Type: jpg Arta SB plus Interface Loop Back THD.jpg (194.0 KB, 289 views)
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Old 9th August 2012, 12:07 AM   #538
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Possible, yes. That's also the spectrum you'd see in severe overload. Chips are cheap- just plug in another one and if that wasn't it, ah well.
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Old 9th August 2012, 12:22 AM   #539
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Thanks SY.

When I set up the loop back test for just the sound card. I started the sweep and then adjusted the volume control until the 1Khz peak was near 0dbFS.

When I set up the test for both, I adjusted the 1khz peak the same. If I reduced the peak down to lets say -80dbFS the THD went down to about .1%

What should the 1khz peak be set at?
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Old 9th August 2012, 12:37 AM   #540
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Depends on the soundcard- gain structure is a bit of an art. If you have to reduce things to -80dB, you either have an issue with the interface or the interface sensitivity is too high. There's a range switch- try setting it to 20V and the soundcard output to 100%.
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