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Old 1st July 2012, 04:28 PM   #101
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From another post on the TI board seems that this problem is apparent in other settings as well. Someone posted about it (sorry don't have the link right now). The suggestion from TI is to install a special driver which works together with a hardware fix as described in the application note (basically adding a good 3V regulator to power the device. A customer on the board says that is solved the problem. My chip is the PCM2902E model, I am wondering if this fixed in other revisions? I can't find all the suffixes on TI's website.
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Old 1st July 2012, 09:47 PM   #102
Simon B is offline Simon B  United Kingdom
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I suspect that the software referred to is a "filter driver" that happens to work with usb audio kit, rather than driver software for an "audio filter".

A filter driver is one type of driver in the windows driver model (WDM), along with bus and function drivers.

WDM on wikip

If you're thinking this might be fun to program, be warned that it's being supplanted by WDF.......
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Old 1st July 2012, 09:56 PM   #103
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For the 1st time I have something good to update!!!
After going through the forums on TI's website I've noticed that someone solved the noise problem simply be feeding a 3.6V DC into Vccci (pin10) which is the internal analog power supply for the codec.
In the kit this pin is decoupled with a cap to ground. I wanted to check the 3.6V fix but didn't have a regulator and it was around 10PM and I hate to wait for tomorrow so I went through stuff I have and found an evaluation board from microchip and it had a 3.3V regulator. I pulled it out together with all the caps and even a coil and using a thin hookup wire and some hot melt glue I bonded everything onto the kit's PCM2902 PCB and plugged it in. I was shocked!!! This actually did the trick! I will post pictures of my amateurish work later today or tomorrow.
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Old 1st July 2012, 10:19 PM   #104
Simon B is offline Simon B  United Kingdom
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Nice one space-cake, and congratulations for ploughing through forums (full of nutters, every last one of 'em ) til you found that.
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Old 1st July 2012, 10:21 PM   #105
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Here we go...

The 1st picture shows the NE PCB with the BB PCM2902E daughter-board in the middle. The 2nd picture shows the regulator (SOT23), 3 caps and 1 inductor. The 3.3V regulator is an MC7100 I think. On the input side there's a 10uF electrolytic cap paralleled with 1uF to ground and a series 10uH inductor. The output side of the regulator has a 1uF cap to ground as well. Output goes to pin10 (Vccci). That's all.
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Last edited by space-cake; 1st July 2012 at 10:24 PM.
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Old 1st July 2012, 10:51 PM   #106
bcmbob is offline bcmbob  United States
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Just curious - what was the function of the original evaluation board? Looks interesting.
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Old 2nd July 2012, 12:08 AM   #107
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Stunning, space-cake. Well done!

It would be good to mention this to Nuova Elettronika and whoever sold you the kit (if it wasn't them). It would seem desirable that this was built into the kit in future.

I'd be interested in hearing how the card works compared to using a normal sound card for this work. What do you see as the advantages?

Terry
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Old 2nd July 2012, 12:18 AM   #108
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Thank you very much for the comments
It might not be clear from the pictures but the small board came with the kit, this is a daughter board for the PCM2902 that NE uses for a few of their projects (including the ZRLC meter I had so much trouble with - perhaps this is why - it uses the same card).

The regulator "section" came from a Microchip MCP3221 evaluation board, however any good regulator will probably work here. TI suggest their own model in one of the applications on the datasheet.

Regarding NE, I wrote them an email and I hope tomorrow someone will be kind enough to bother to read it. The response I've received for my 1st email was something like: "this kit is great people use to design tube amps". Not a single word on anything specific I wrote them. I have little faith they will do anything with the information. As I said, they use this module in a number of their kits and even though this only means that the small board needs to be populated with a few extra components I do not expect this from someone who did not test (?!?) the kit before selling it. This also brings up the question who buys these kits? Where is everyone? Isn't there at least one other person who saw this post and owns the kit? Very strange...

I will compare the card to my VIA sound card, intended to do that anyway and at least now I'll have some use for the 3.5mm jack to BNC junction box I bothered to make after initially giving up on the NE kit. What I can say at this point without special testing is that the internal sound card suffers from some noise at higher freq., if I remember correctly above 18.5KHz but these are pretty weak so probably won't interfere with measurements too much.

Last edited by space-cake; 2nd July 2012 at 12:23 AM.
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Old 2nd July 2012, 12:42 AM   #109
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Quote:
Originally Posted by space-cake View Post
Regarding NE, I wrote them an email and I hope tomorrow someone will be kind enough to bother to read it. The response I've received for my 1st email was something like: "this kit is great people use to design tube amps". Not a single word on anything specific I wrote them. I have little faith they will do anything with the information. As I said, they use this module in a number of their kits and even though this only means that the small board needs to be populated with a few extra components I do not expect this from someone who did not test (?!?) the kit before selling it. This also brings up the question who buys these kits? Where is everyone? Isn't there at least one other person who saw this post and owns the kit? Very strange...
I guess it also reminds us of the divide that language makes. Here we have NE publishing some really interesting stuff (although, as you point out, seeming not to test it very thoroughly!), but we are locked out of it by not speaking Italian. And the presumably many Italians who would have bought and used the kit are probably mostly locked out of DiyAudio by not speaking English.

Quote:
I will compare the card to my VIA sound card, intended to do that anyway and at least now I'll have some use for the 3.5mm jack to BNC junction box I bothered to make after initially giving up on the NE kit. What I can say at this point without special testing is that the internal sound card suffers from some noise at higher freq., if I remember correctly above 18.5KHz but these are pretty weak so probably won't interfere with measurements too much.
I look forward to hearing the results of your tests! I'm still wondering about building such a card into my proposed control unit to avoid noise pick-up en route to the computer.

It's perhaps surprising that, if they were going to the trouble of designing a special card, they didn't opt for a wider bandwidth than the usual sound card. I'd have like DC to say 48k (bandwidth, so DC coupled and 96k or more sampling speed), just so the limits of the card are well beyond the audio band extremes. But maybe that's just too hard?

Do you know if you can get significantly closer to DC by increasing coupling capacitors, or is there some other limiting factor in the system at the LF end?

Terry
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Old 2nd July 2012, 01:15 AM   #110
bcmbob is offline bcmbob  United States
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If you found some new Italian documentation I would again suggest it be shown to Dario Inserra. He is Italian and very active on the forums. I don't know if he is still watching this thread.
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