Chokes for SE class A

djk · 09:12 AM

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)
---------------------------------------------------------------------
"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)

Magura · 7th February 2010, 09:46 AM

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

Magura

woody · 7th February 2010, 10:01 AM

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!

Magura · 7th February 2010, 10:18 AM

Here is a little reading to start you out:

Choky Susy F3 for LU1014's

Magura

Zen Mod · 7th February 2010, 05:34 PM

that's sissy amp ; it demands 20R NTC to salvage local area power ring , during starting

Magura · 7th February 2010, 06:16 PM

Hey, it's not a real amp, if it doesn't dim the lights a bit at startup

Magura

djk · 7th February 2010, 10:14 PM

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)?

woody · 7th February 2010, 10:57 PM

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.

Magura · 8th February 2010, 05:42 AM

That is good advice Woody.

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

Magura

miklos · 8th February 2010, 07:05 AM

Could you please describe the issues closer?
Thanks.

7th February 2010, 09:10 AM	#1
djk diyAudio Member Join Date: Feb 2001 Location: USA	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) --------------------------------------------------------------------- "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) __________________ Candidates for the Darwin Award should not read this author. Last edited by djk; 7th February 2010 at 09:12 AM.

7th February 2010, 09:46 AM	#2
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	Well, you need much higher inductance. 2 x 80mH is barely enough. Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

7th February 2010, 10:18 AM	#4
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	Here is a little reading to start you out: Choky Susy F3 for LU1014's Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

7th February 2010, 05:34 PM	#5
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	that's sissy amp ; it demands 20R NTC to salvage local area power ring , during starting __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio-EX YU DiyA FORUM

7th February 2010, 06:16 PM	#6
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	Hey, it's not a real amp, if it doesn't dim the lights a bit at startup Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com


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7th February 2010, 10:01 AM	#3
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	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!

7th February 2010, 10:14 PM	#7
djk diyAudio Member Join Date: Feb 2001 Location: USA	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)? __________________ Candidates for the Darwin Award should not read this author.

7th February 2010, 10:57 PM	#8
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	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.

8th February 2010, 05:42 AM	#9
Magura diyAudio Member Join Date: Oct 2003 Location: Denmark, Viborg	That is good advice Woody. I have experimented with cored inductors, and DC seems to cause issues. Magura __________________ Everything is possible....to do the impossible just takes a little while longer. www.class-a-labs.com

8th February 2010, 07:05 AM	#10
miklos diyAudio Member Join Date: Jul 2004 Location: toronto	Could you please describe the issues closer? Thanks. __________________ miklos

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