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-   -   The Kuartlotron - keantoken's simple error-correction superbuffer (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer.html)

 keantoken 6th March 2014 04:39 PM

1 Attachment(s)
Quote:
 Originally Posted by Joachim Gerhard (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3844576.html#post3844576) 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.

 ammel68 6th March 2014 04:43 PM

Quote:
 Originally Posted by Joachim Gerhard (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3844471.html#post3844471) 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...

 Joachim Gerhard 6th March 2014 06:24 PM

 keantoken 6th March 2014 06:55 PM

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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?

 Joachim Gerhard 6th March 2014 08:06 PM

1 Attachment(s)
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.

 keantoken 6th March 2014 08:25 PM

1 Attachment(s)
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.

 ammel68 6th March 2014 09:45 PM

Quote:
 Originally Posted by Joachim Gerhard (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3844790.html#post3844790)
Thank you!

 Joachim Gerhard 6th March 2014 11:40 PM

Very nice Kean. I look forward to trim your buffer too.

 keantoken 7th March 2014 04:38 AM

In my previous post #2 should read 6.09V, not 5.9V. D'oh!

 baswamin 7th March 2014 04:48 AM

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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