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Old 23rd June 2012, 06:46 AM   #91
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So it could still be VA or it could still be the NE kit interface. Does the interface come up in My Computer as a sound card? If you loaded another generator/FFT package can you tell it to use the kit? Try the package at Soundcard Scope. You specify which input and output device to use in the Settings tab. Use it to generate the signal and to do FFT on it and see if the mystery sidebands are also there.

Terry
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Old 23rd June 2012, 09:49 AM   #92
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Downloading another software is a good idea!
So I downloaded what was suggested and installed on one of my computers. I connected the scope kit and it is recognized as a normal USB sound card. I loaded the scope program and the second i connected the scope probe to the wave generator output... well, you can see. I think this means the kit is the source of the noise, perhaps the wave generator part specifically.
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Old 23rd June 2012, 11:03 AM   #93
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Now, wait just a minute! That's an extraordinary amount of harmonic activity for a sine wave. What happens if you now switch to the oscilloscope panel and view the waveform. Is it clipped or otherwise mangled? Can you post a screen grab?

Hmmm, your version of Scope is a bit different to mine. Mine doesn't have the dB box. What version is that?

Terry
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Old 23rd June 2012, 11:13 AM   #94
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Quote:
Originally Posted by Terry McGee View Post
Now, wait just a minute! That's an extraordinary amount of harmonic activity for a sine wave. What happens if you now switch to the oscilloscope panel and view the waveform. Is it clipped or otherwise mangled? Can you post a screen grab?

Hmmm, your version of Scope is a bit different to mine. Mine doesn't have the dB box. What version is that?

Terry
Terry, no one said that the noise is a sine wave
It happened to be that the custom wave I was generating using VA was a series of sines which was important because otherwise it could have been harmonics generated by my wave and not another source. This is way too much harmonic content for a sine, I agree. Even if it was a little bit clipped I would expect to see a small amount of 2nd maybe 3rd harmonic but not more and not this much!

The version is 1.4 from the link you've posted. Included is a screen capt., this is about as good of a picture I can get of it.
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Old 23rd June 2012, 11:38 PM   #95
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Ah, silly me. So, the nasty 1kHz signal appears to be emanating from the NE kit card. What frequency does the DC-to-DC converter (transistors Tr1 and Tr2, T1) run at?

Terry
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Old 24th June 2012, 06:50 AM   #96
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Just a bit under 65KHz.

I managed to get an answer from NE regarding support, they promised that someone is going to call me tomorrow. The idea of asking for a refund was a good one! Thanks!
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Old 24th June 2012, 08:23 AM   #97
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Yeah, I thought it was likely to be high rather than low. There's nothing else in the schematic that should be singing (unless your schematic is different to the one published in the article). Apart from the crystal oscillator in the big chip, but surely that has to be high. (The parts list in the article doesn't mention the xtal 1 frequency, but 1KHz would be a very big crystal!) And 1kHz is very low for a spurious oscillation. Very strange.

Best of luck, and keep us informed!

Terry
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Old 1st July 2012, 11:51 AM   #98
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From TI support... This might be the problem!!

http://focus.ti.com/lit/ug/slau238/slau238.pdf
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Old 1st July 2012, 12:50 PM   #99
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That's pretty weird, space-cake! The errata document cited suggests "Only the 0A (16 kHz, 16 bits, Mono mode) setting creates the noise problem." But that's hardly the setting used in the VA application? Surely VA would opt for the widest bandwidth, greatest bit number, stereo setting?

But against that, what is the probability that they found exactly the same problem you found? Is the problem perhaps more widespread than they think?

But then, going on from there, installing a filter? Does that suggest that the codec will filter out all 1KHz signals? That wouldn't be handy!

Keep us posted!

[Aside to audience. Don't the days of analogue seem suddenly strangely attractive?]

Terry
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Old 1st July 2012, 01:54 PM   #100
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Wow, that's a strange one. I've certainly used the 2900 series chips before with no apparent problem. The series is pretty common for USB audio.
Watching to see what you find.
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