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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)

danielwritesbac 9th March 2014 11:35 PM

Rather orgasmic to be able to crank up your system loud without the blare.
Link: Kean's common mode choke

Trileru 10th March 2014 10:56 PM

1 Attachment(s)
I found a CM choke in a failed computer PS. It looks identical as the one in the link only that it measures about 10mH on each winding. Would that do? I saw that a 20mH one is recommended. I could look for some more as I have access to some failed computer PS.
I might try this over the weekend if I get some spare time.

keantoken 10th March 2014 11:32 PM

The effect should be audible down to a few mH because at 1KHz the fault rejection is much higher than at 60Hz (it doubles every octave) . Of course you may not hear a difference if you don't have ground noise problems, but I think it's very unlikely you don't have any ground noise.

The benefit of a large choke is that it has more of an effect in the bass, to my ears. 10mH will be no worse than a 5R groundlift resistor, which isn't bad. I'm using 15mH right now, since it's the largest I have. 5mH is enough to significantly reduce 60Hz ground fault current.

keantoken 10th March 2014 11:39 PM

Does this mean you want to try the virtual ground bootstrap, or do you have another plan? Either way, the CM choke could be helpful.

taisho_daniel 11th March 2014 12:23 PM

I'm playing around with the same DAC chip (AK4396), and I'm willing to try out using the virtual ground bootstrap idea. :)

Have most of the parts lying around in my spare bin, with the exception of the 2700k pot, 15pF cap, and the inductor.

EDIT : If I were to use this to implement a low pass filter as well as the bal -> se conversion, would it be just as simple as placing the components across the + - legs? Or should there be one set each of low pass filter components for both + and - legs, connected to ground?

Trileru 11th March 2014 12:38 PM

Quote:

Originally Posted by keantoken (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3850327.html#post3850327)
Does this mean you want to try the virtual ground bootstrap, or do you have another plan? Either way, the CM choke could be helpful.

Yes, I'd try the virtual ground bootstrap. I have the inductor and need to source the transistors, but should be ok. I might go to the store today. Any idea on how to test those transistors for better matching with dmm/oscilloscope? :)

Ken Newton 11th March 2014 04:24 PM

Quote:

Originally Posted by Trileru (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3850285.html#post3850285)
I found a CM choke in a failed computer PS. It looks identical as the one in the link only that it measures about 10mH on each winding. Would that do? I saw that a 20mH one is recommended. I could look for some more as I have access to some failed computer PS.
I might try this over the weekend if I get some spare time.

The following caveat should be mentioned regarding the use of common-mode chokes in a signal coupling application. Common-mode chokes exhibit leakage inductance. This leakage inductance will appear as a normal-mode impedance. In other words, it will impede the desired normal signal conduction. This is a useful parasitic effect in power supply applications, where you then obtain common-mode noise choking, plus some small amount of bonus normal-mode noise choking from the same component.

Although this leakage inductance will be a small fraction of the common-mode inductance, in conjunction with the interconnect's and the following stage's shunt input capacitance, it will produce an unintended second-order low-pass filtering of the signal. Before selecting the specific common-mode choke you will use, you should compute how this unintended low-pass filter will impact the desired signal's frequency response. If you are clever and lucky, you could engineer this unintended filter to help reject the ultrasonic image and noise content produced by your DAC.

You should find the leakage inductance specified in the common-mode choke's datasheet.

Trileru 11th March 2014 08:38 PM

1 Attachment(s)
Quote:

Originally Posted by Ken Newton (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3851118.html#post3851118)
The following caveat should be mentioned regarding the use of common-mode chokes in a signal coupling application. Common-mode chokes exhibit leakage inductance. This leakage inductance will appear as a normal-mode impedance. In other words, it will impede the desired normal signal conduction. This is a useful parasitic effect in power supply applications, where you then obtain common-mode noise choking, plus some small amount of bonus normal-mode noise choking from the same component.

Although this leakage inductance will be a small fraction of the common-mode inductance, in conjunction with the interconnect's and the following stage's shunt input capacitance, it will produce an unintended second-order low-pass filtering of the signal. Before selecting the specific common-mode choke you will use, you should compute how this unintended low-pass filter will impact the desired signal's frequency response. If you are clever and lucky, you could engineer this unintended filter to help reject the ultrasonic image and noise content produced by your DAC.

You should find the leakage inductance specified in the common-mode choke's datasheet.

That is good info, thank you! I'm learning lots from you guys!
I typed on google the codes on this choke but nothing came up. If I can't find the datasheet I'm going to take the data from the one posted already. I saw that there are 10mH versions for that as well so they might have similar specs. Or anyway, not far off.

Ken Newton 11th March 2014 08:53 PM

Quote:

Originally Posted by Trileru (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3851416.html#post3851416)
That is good info, thank you! I'm learning lots from you guys!
I typed on google the codes on this choke but nothing came up. If I can't find the datasheet I'm going to take the data from the one posted already. I saw that there are 10mH versions for that as well so they might have similar specs. Or anyway, not far off.

If you cannot locate the datasheet, you could go forward and find whether you subjectively notice any treble roll-off effects. If you do not, then no worries. However, common-mode chokes of the values being discussed are relatively inexpensive. You could simply purchase new units having the desired properties, rather than re-purpose mystery units from a PC power supply. If this choke were simply to be used within your DAC's power supply, I would feel less concerned. Seeing that it will be placed in the signal path, however, I suggest extra care in applying it.

smms73 11th March 2014 09:19 PM

Quote:

Originally Posted by Ken Newton (https://www.diyaudio.com/forums/analog-line-level/251413-kuartlotron-keantokens-simple-error-correction-superbuffer-post3851118.html#post3851118)
You should find the leakage inductance specified in the common-mode choke's datasheet.

One can also measure the leakage inductance of an unknown CM choke, by shunting one coil and measure the other.


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