Design of output inductor for class D amplifier

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#42
Chris: I can appreciate your any opinion, but maybe you should seek help with that attitude problem.

For one thing i am surprised you again accuse me of 'marketing babble'. If you look through the whole thread, i have not tried even once to further my product, it's true, i have given my e-mail address to one guy, so i can get in contact with him to send him some ferrite cores to play with. My e-mail address has my brand in it, but i don't think that qualifies as 'marketing babble'.

Give it a rest
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Pink Mouse: Thankyou for showing that link, very interesting. I hadn't seen that thread until now 🙂
 
#43
Pinkmouse, bad joke at best.

Lars, my attitude is no concern to you whatsoever, so give that a rest.

You can try to twist this anyway that you like, but while you're doing so, you could be off doing the mentioned tests .. Mr. "no time".

I get the impression that just about everything surprises you. Here's another shocker.. look at your sig.

Now let's see those test results Eva mentioned, which you have no time for, so we can see if you're just here babbling or not, because trying to provoke me just isn't going to prove your case. :whazzat: In fact it does more to prove mine ...baabububaah babububaaaabler.
 
#44
Lars,

I couldn't stay away, so please humor me, how did you actually design your inductors for newclassd? By listening to several ideas/concepts, or doing it the proper way around, by applying math and measurements? You'll notice than when you hit the sweet spot, ie. the math lines up, and it measures well, it'll automagically sound good too. The only downside is that it requires considerably more effort on the part of the designer, selecting a proper core material and type can be challenging to start with. Hence the topic of this thread, which has been a worthwhile read up till about a few posts ago when we went off-topic with 'how does it sound' comments.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com
 
#46
SSassen said:
Lars,

I couldn't stay away, so please humor me, how did you actually design your inductors for newclassd? By listening to several ideas/concepts, or doing it the proper way around, by applying math and measurements? You'll notice than when you hit the sweet spot, ie. the math lines up, and it measures well, it'll automagically sound good too. The only downside is that it requires considerably more effort on the part of the designer, selecting a proper core material and type can be challenging to start with. Hence the topic of this thread, which has been a worthwhile read up till about a few posts ago when we went off-topic with 'how does it sound' comments.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com
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And so it begins again ...... :dead:

Sorry guys of the esteemed wolfpack / and dutch flaming squad (from other now-shut-down-for-this-exact-reason threads). I can tell you one thing i don't have time for ..... Life is too short 😉

Moderators: Please remove the last 9 posts, keep your forum clean. Thanks! 🙂
 
#47
Dear Lars. Try to be nice, talk a little more respectfully to your fellow DIY'ers. Sander's question is just as decent as anything else written in this thread. In any case i don't think this forum is only for the 'elite' in any particular subject. Anybody should have the right to participate on an equal basis, we are all experts on some subjects, and amateurs on other subjects. Doesn't give some (you) the right to deem other peoples rightful questions in-decent. I hope you agree.


You should have just stayed on topic as requested.. I was playing with matches back in kindergarden. So I'll have some probes in a few weeks 😉

"Moderators: Please remove the last 9 posts, keep your forum clean. Thanks! "

agreed. But I'm still posting those test results if you won't.
 
#49
classd4sure said:
I truly understand your wanting to defend the question, but I just can't bring myself to agree, or sit by while an otherwise very good and possibly educational thread, one of the few in a long time at that, gets dragged down into the obvlivion of subjective marketing babble.
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As a third party observer it does not seem as though Lars has any hidden agenda and further more he offered to send someone some free cores! C'mon he's just adding some value to the conversation. He may eventually get around to doing those measurements but as most of us know, there are more important things in life that can eat up any and all free time that comes along (i.e. women, girlfriend, wife, eating, sleeping, etc.).

SSassen said:
I couldn't stay away, so please humor me, how did you actually design your inductors for newclassd? By listening to several ideas/concepts, or doing it the proper way around, by applying math and measurements?
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Lars stated what kind of cores he's using (I think there he gave some air gap dimensions too) as well as how he wound them. I don't know all the math required to figure out if his inductor design goes by the numbers or not, but I'm sure he at least applied some engineering knowledge when designing the inductor.
 
#50
Hi Lars

I once posted this question:

I see ! so how does this one compare to the 3F3 RM core that you showed some posts ago (the one with the air-gapped central leg) ? How much do they differ in terms of non-linearity (all other things being equal) ?
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So how do they compare ? At what current do they go into saturation ?
I once derived the formulae to calculate the Al-value and Bmax when an airgap is introduced. Their accuracy was heavily dependant on core type since they assumed a constant cross section of the magnetic path which is an idealisation of course.

Did you ever measure the distortion added by the output filter ? and did you compare this for the two cores as well ?

Regards

Charles
 
#51
phase_accurate said:
Hi Lars

I once posted this question:



So how do they compare ? At what current do they go into saturation ?
I once derived the formulae to calculate the Al-value and Bmax when an airgap is introduced. Their accuracy was heavily dependant on core type since they assumed a constant cross section of the magnetic path which is an idealisation of course.

Did you ever measure the distortion added by the output filter ? and did you compare this for the two cores as well ?

Regards

Charles
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Hi Charlies,

I'd be interested in your take on this :

http://www.fairchildsemi.com/an/AB/AB-12.pdf#search="switching inductor core soft saturation"

Particularly their statements on "soft saturation" and the rod core.

Thanks
 
#52
(i.e. women, girlfriend, wife, eating, sleeping, etc.).
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...None of which i have time to enjoy. But Thanks just the same 😀

Charles: Thanks for your very qualified (as always) discussion. You are of course hitting the problem right on, the coil is - as you most probably know - the key to further lowering THD of the amplifier. And therefore will be the target for further design improvements in the future. I would be interested to get any help possible on this matter, as i begin to realize there are a huge number of variables in this equation. (Especially when you start digging into the subject). In no way do i claim to be an expert on Ferrite's. I have very skilled people to ask for help, but they are unfortunately not audio people. One is Mr. Vilceanu, who should be well known in the more knowing circles of Ferrite design.

Saturation of the coil, see below photo. 10 Ampere per div.

sat.jpg
 
#53
classd4sure said:
Particularly their statements on "soft saturation" and the rod core.
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I'm not terribly qualified to respond to that but here's a bit of info from Pulse that makes sense.

http://www.findarticles.com/p/articles/mi_m0EIN/is_2005_May_5/ai_n13672629

"The unshielded drum core has a narrow center rod with a flat disc on each end. The inductor wire is wound on the rod between the discs. The inductor is an energy storage device which stores energy in an air gap in the flux path of the inductor. For the unshielded drum core inductor, this air gap is between the two end discs. The flux path is through the center rod, outwards through one disc, through the air gap around to the outside of the other disc, and inwards through the second disc. The unshielded drum core is a lower cost technology and the larger energy storage air gap allows it to support higher peak currents without saturation effects.

In the shielded drum core inductor, an additional ferrite cylinder is located around the outside of the two discs and guides the flux between the discs through the cylinder. The discrete air gap is the combination of the gaps between each end disc and the ferrite cylinder. Because the additional ferrite cylinder keeps the flux in a controlled path, shielded drum core inductors are better for applications where the stray flux of the unshielded drum core may interfere with nearby noise-sensitive electronics or where electromagnetic interference (EMI) is a concern. The shielded drum core inductor has a higher inductance for the same number of wire turns than the unshielded inductor due to the smaller air gap and higher permeability of the ferrite cylinder."

And this EDN article is an interesting read too.

http://www.edn.com/article/CA6325598.html?ref=nbra
 
#55
The large external air gap means a large external magnetic field (not well contained). That's obviously a bad thing, especially for higher power class d amps where all the circuitry (signal and power) is in such a small area.
 
#59
If you have the airgap on the middle leg only (like on Lars' picture) then the external stray-field is smaller. But now the winding itself is more exposed to the stray-field. So it would be best to upholster the coil former in order to keep the windings as far away from the center leg as possible.

Lars, have you ever compared two coils, one having the airgap on the center leg only and the other one on center and outer leg but with otherwise equal properties ?

Regards

Charles
 
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