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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 9th March 2014, 11:35 PM   #131
danielwritesbac is online now danielwritesbac  United States
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Rather orgasmic to be able to crank up your system loud without the blare.
Link: Kean's common mode choke
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Old 10th March 2014, 10:56 PM   #132
Trileru is offline Trileru  Romania
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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.
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Old 10th March 2014, 11:32 PM   #133
keantoken is offline keantoken  United States
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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.
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Old 10th March 2014, 11:39 PM   #134
keantoken is offline keantoken  United States
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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.
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Old 11th March 2014, 12:23 PM   #135
taisho_daniel is offline taisho_daniel  Philippines
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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?

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Old 11th March 2014, 12:38 PM   #136
Trileru is offline Trileru  Romania
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Originally Posted by keantoken View Post
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?
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Old 11th March 2014, 04:24 PM   #137
Ken Newton is offline Ken Newton  United States
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Quote:
Originally Posted by Trileru View Post
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.

Last edited by Ken Newton; 11th March 2014 at 04:38 PM.
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Old 11th March 2014, 08:38 PM   #138
Trileru is offline Trileru  Romania
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Originally Posted by Ken Newton View Post
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.
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Old 11th March 2014, 08:53 PM   #139
Ken Newton is offline Ken Newton  United States
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Quote:
Originally Posted by Trileru View Post
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.
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Old 11th March 2014, 09:19 PM   #140
smms73 is offline smms73  Europe
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Originally Posted by Ken Newton View Post
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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