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The Kuartlotron - keantoken's simple error-correction superbuffer
The Kuartlotron - keantoken's simple error-correction superbuffer
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Old 6th March 2014, 04:39 PM   #111
keantoken is offline keantoken  United States
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Quote:
Originally Posted by Joachim Gerhard View Post
Can you show the measurements ?
What is the input impedance of your soundcard ?
I have a 2-minute 10KHz sine wave measurement I could send by email, but it's a large file.

Here is an image of those 2 minutes averaged in an FFT. The 2nd harmonic can't be measured, and the 3rd harmonics could easily be spectral noise. The Kuartlotron input is subtracted from the output, which is why the fundamental is low.

I don't know what the impedance of my soundcard is, but I suspect it's not very high.
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File Type: png Kuartlotron_FFT.png (505.2 KB, 844 views)
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Old 6th March 2014, 04:43 PM   #112
ammel68 is offline ammel68  United States
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Quote:
Originally Posted by Joachim Gerhard View Post
The AD797 can be made as a stable buffer easy.
Care to provide a link or a diagram showing a circuit using it as a unity gain buffer?
Thanks...
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Old 6th March 2014, 06:24 PM   #113
Joachim Gerhard is offline Joachim Gerhard  Germany
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Page 10 :http://ezphysics.nchu.edu.tw/prophys...heet/ad797.pdf
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Old 6th March 2014, 06:55 PM   #114
keantoken is offline keantoken  United States
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Okay, I figured out how to get the lowest noise floor on my soundcard. I also made a mistake in calculating THD. H2 is at -96db, so THD is about .0016%. This is at 1V pk-pk input.

While this measurement is more than I've gotten in the past, it's pretty good considering that my Kuartlotron as it's running right now is out of trim because I had to use a higher voltage supply. It may be able to lower it by trimming.

EDIT: Attached FFT.

PS. This is coming from ONBOARD sound on an Asus M5A99FX Pro R2.0 motherboard. Surprising?
Attached Images
File Type: png Kuartlotron_FFT.png (478.8 KB, 803 views)
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Old 6th March 2014, 08:06 PM   #115
Joachim Gerhard is offline Joachim Gerhard  Germany
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We measured 0.003% THD plus noise at 1V RMS so this is not far off.
Anyway, i do not think that this amount of distortion is audible.
When you ask me : What sounds good ?
Elegant and sofisticated simplicity.
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File Type: png Kean dist.png (97.4 KB, 762 views)
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Old 6th March 2014, 08:25 PM   #116
keantoken is offline keantoken  United States
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My experience is in agreement Joachim, and a friend has sternly told me that this buffer sounds great even when it's not working optimally. So while THD is low, that does not seem to be the reason this buffer sounds good.

Still, for those who want to know, here is the FFT after trimming. H2 is at -112db. That is 0.0002%THD at 1V pk-pk input!

So, without trimming you can expect THD around .001-.003%, and after trimming you can expect THD down to .0002%. That matches the simulation very well. I think the path forwards from here is not necessarily to lower THD, but to design the circuit so that it gets lower non-trimmed distortion.

Here's what I did:

1: My power supply is +-12.18V.
2: Adjust R5 so that TP is at 5.9V.
3: Adjust R1 for best THD null, watchingt TP for reference.
4: TP ended up at 4.85V at the optimal trim point.
5: Your trimming results may vary.
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File Type: png Kuartlotron-trim_FFT.png (803.7 KB, 751 views)
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Last edited by keantoken; 6th March 2014 at 08:29 PM.
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Old 6th March 2014, 09:45 PM   #117
ammel68 is offline ammel68  United States
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Originally Posted by Joachim Gerhard View Post
Thank you!
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Old 6th March 2014, 11:40 PM   #118
Joachim Gerhard is offline Joachim Gerhard  Germany
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Very nice Kean. I look forward to trim your buffer too.
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Old 7th March 2014, 04:38 AM   #119
keantoken is offline keantoken  United States
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In my previous post #2 should read 6.09V, not 5.9V. D'oh!
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Old 7th March 2014, 04:48 AM   #120
baswamin is offline baswamin  India
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Kean,

What is the value of R1 after trimming? I dont have equipment to measure THD but want to know if there is some other way of getting lowest THD without measurement.
Anyway, I listened to it more yesterday and it is very good for sure. High frequency retrieval is amazing (atleast in my setup).

Thanks
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