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speakerguy79 20th January 2009 11:22 PM

Shielded or Toroidal Inductors for Class D output filter
Does anyone have a good source for inductors for a high power (100W@8R, 200W@4R) class D output filters? I like the looks of the TOKO DASM1620 series but I can't find anywhere to buy them.

thespeakerguy 23rd January 2009 08:40 PM

DC-DC Converter Inductors work well
not as a blanket statement, but if properly selected.

I found the coilcraft DO3340 to be very linear, but they are not high enough power for what you ask. These are not shielded, which helps with their linearity, but they can crosstalk between adjacent channels

If using a DC-DC inductor, its best to have a good margin of current. Make sure the graph of inductance as a function of current is flat across the range you wish to use it.

speakerguy79 23rd January 2009 11:01 PM

Thanks for the reply. Right now I am looking at the JW Miller / Bourns 2300LL (low loss) series. They are rated to 20A for 10uH and slightly less current for 15 or 22uH.

I found searching on this forum that someone used the smaller 2200LL series with success on a Tripath amplifier. What do you think of the 2300LL? I may try to order some and put them on the TAS5518/TAS5261 stereo eval board I have here.

Eva 24th January 2009 01:06 AM

It's not that hard to design and build your own custom inductors. Suitable cores are available at several online shops.

Anthony C Smith 24th January 2009 03:37 PM

Wurth electronics do some great pre made inductors for class D; like the 10u 20A inductor 7447180 data :
low cost and they do a range of values suited to 2,4 and 8 ohm loads- the ferrite bar appears to soft saturate, however carefull design and layout is required as they bleed like pigs!

classdphile 25th January 2009 07:19 AM

Yeah, that's why careful design mandates not using them.

speakerguy79 28th January 2009 02:20 PM

What about Kool Mu cores from Magnetics Inc? That is apparently what J.W. Miller uses in their 2100LL/2200LL/2300LL "Low Loss" series, and those are readily available.

I also contacted a company about getting some 1.3" diameter MPP toroids and they wanted $8.50 for the cores alone.

Anthony C Smith 31st January 2009 02:20 PM


Originally posted by classdphile
Yeah, that's why careful design mandates not using them.

I am becoming increasingly annoyed by your critisism allied to your lack of contribution; these parts are designed for output filters and soft saturate- which is good; the fact they are a ferrite bar requires carefull layout and mechanical design, of interest to the many here who have hobby and commercial reasons to share their common experiences.

I do not know you or your background, I can only read your posts, English may not be your first language, however you are one of the most negative people I have come across, the replies you make do not contribute, rather deride or enflame, and as the old phrase goes if you have nothing to contribute please don't comment (highly edited to prevent offence)

I am a hobbist and a professional designer, my products are independantly tested and carry certificates to prove this, others on this forum also are involved in the professional allied arts, so we are all in this together.

I like this forum as a repository of knowledge, sharing and understanding, and feel loathed when it contains put downs and bad feelings, I appeal to you to consider others before you post, or find some other medium to vent your feelings.

classdphile 31st January 2009 07:03 PM

You're either a hobbyist or you're a professional, not both. Each posts from a certain perspective and for different reasons. As you so often include your credentials, though english may not be my first language there's no doubt as to which you choose to portray.

Invoking hurt feelings when there was nothing personal there, to outright ad hominem such as this, are just fallacies that detract from your professionalism or the sageness that goes with it.

As a professional that wishes to be taken at a higher level as you clearly do per your chorous of credentials, you could better appreciate the scrutiny that can go along with it rather than supposing yourself above it and still expecting to reap whatever benefits. I still await your correction on the NTC soft start for class d. I felt that friendly tip would have gotten you thinking about it, but evidently you can't be wrong.

Rod cores have their uses, this isn't it. I hope this doesn't otherwise take away from our friendship.

Ouroboros 2nd February 2009 07:09 AM

Ordinary gapped RM cores are a very good basis for output filter inductors. They are available in the right sort of AL values (160 or 250 nH/turn), and are available in 3F3 ferrite, which works well at class-D switching frequencies.

Alternatively the range of precision-gapped ferrite toroids from Ferroxcube (designed especially for class-d output filters), have very low losses, although the core sizes available are only really of use for output filters for amps up to 250W or so.

I've had bad results from other toroidal powder cores. They work, but the core losses are too high for me to be happy with them.

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