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Old 7th February 2010, 09:10 AM   #1
djk is offline djk
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Default Chokes for SE class A

Does this sound like a reasonable idea to try for the constant current choke on a single-ended class A amplifier?

"there is a trick that can actually increase the inductance and mostly cancel core saturation. Take two I-cores, stack them end to end, the closer the better (epoxied together for long term use is best), and run them in reverse magnetic polarity while in series. This can allow you to use a smaller initial value of inductor, and keep core saturation to a minimum. For instance if your goal is 10 mH, you don't need two 5 mH inductors, but more like two 3 to 4 mH inductors, the exact value depends on how closely coupled the cores are.

If you had inductors rated to handle say, 5 amps each, when configured in this manner, they might be able to take 15-25 amps or so, depending on how well matched and positioned the cores are.

Ideal implementation has two bobbins on a single long laminated core, no air gap losses then." (Jon Risch)
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"big thanks Jon , I found two 1mH Madisound steel core inductors and twisted the leads to put them in series. I'm not sure if I got all the permutations available as I didn't change the lead connection - but did change one core's orientation.

Inductance measured ~2.1mH with cores spaced, 1.75mH with in one butted position, and 4.15mH in the other. Did I leave out something as one position was double the inductance? Out of the conditions tested which one is the preferred?" (Fred I)
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Last edited by djk; 7th February 2010 at 09:12 AM.
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Old 7th February 2010, 09:46 AM   #2
Magura is offline Magura  Denmark
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Well, you need much higher inductance. 2 x 80mH is barely enough.

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Old 7th February 2010, 10:01 AM   #3
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This has been talked about before. Nelson even has an example of this in the ZEN 7
article found at Passdiy.com. But as Magura pointed out for good base responce you
will need a large inductor 50mh might do for use in a midrange amp. And large inductors tend to be hard to find and expensive!
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Old 7th February 2010, 10:18 AM   #4
Magura is offline Magura  Denmark
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Here is a little reading to start you out:

Choky Susy F3 for LU1014's

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Old 7th February 2010, 05:34 PM   #5
Zen Mod is offline Zen Mod  Serbia
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that's sissy amp ; it demands 20R NTC to salvage local area power ring , during starting

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Old 7th February 2010, 06:16 PM   #6
Magura is offline Magura  Denmark
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Hey, it's not a real amp, if it doesn't dim the lights a bit at startup


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Old 7th February 2010, 10:14 PM   #7
djk is offline djk
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I guess I should have given more detail, the question was really about the winding technique and core saturation in a DC application.

Do any of you know the answer to that?

"Well, you need much higher inductance. 2 x 80mH is barely enough."

Thanks, I think most people can figure that out.

How much inductance do you think is actually needed for a high frequency amp (400hz and up)? How about for a VHF amplifier (4Khz and up)?
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Old 7th February 2010, 10:57 PM   #8
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I would expect for 400hz up a 20mh choke would work and for 4kup a 2mh choke.
Aswsuming a 8ohm speaker. For these values I would use aircore chokes. 2.5 lbs
of 16 gage magnet wire using a 1/2" core .75" long will give you about 20mh.
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Old 8th February 2010, 05:42 AM   #9
Magura is offline Magura  Denmark
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That is good advice Woody.

I have experimented with cored inductors, and DC seems to cause issues.


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Old 8th February 2010, 07:05 AM   #10
miklos is offline miklos  Canada
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Could you please describe the issues closer?
Thanks.
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