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Old 22nd January 2007, 01:53 PM   #1
ypasco is offline ypasco  Canada
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Default THe conclusion about the output coils

What is the conclusion about the output filtering coils used in the amp5/amp1/amp1b.... I read the whole topic about this and still can't make any conclusions...

any strong hints from thomas, bertus, etc...

Yann
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Old 26th January 2007, 04:36 PM   #2
cotdt is offline cotdt  United States
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I was going to try thomaseliot's technique of using the special exotic material cores, but instead I unwound a 50uH Jantzen air foil inductor to 11mH using my RC meter (they are dirt cheap these days, btw). I wrapped the ends of the foil around wire sticks to mount them onto the PCB, one on each side of the board. I figured why not just go all the way and use air core? Well, I was right! The improvement was dramatic on my AMP5! Another important mod was to get rid of all input and output filter capacitors. Well, although I DC-coupled the input, the onchip opamps in the Tripath chip generates DC current, so that sometimes tripped the protection. In the end, I had to use the input capacitors after all. I don't beleive in exotic capacitors, all that audiophile hype! I decided to use Mundorf M-CAP RXF which is specially designed for this purpose, and quite cheap. If I had the money I would go for liquid Fluorinert caps, though.
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Old 26th January 2007, 08:28 PM   #3
ypasco is offline ypasco  Canada
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Thank you for your reply.

are the inductor the air one from partsexpress ?

as i can't measure the inductance do you remember how much coopen you have unwounded ?

Do you have troubles with EMI radiations ?

and finally : about heat dissipation : are the inductors hot ?


thxs

Yann
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Old 26th January 2007, 09:10 PM   #4
cotdt is offline cotdt  United States
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Yes, I got mine from Parts Express for a speaker project that never came to be. Parts Express also sells the exact 11uH foil inductors, but it's not on their catalog and there is a wait time. Yes, I can tell you how much to unwind, but I don't have a long enough ruler, so it will take some time to measure. If you're still interested, email me and I'll tell you.

No EMI troubles. Commercial Tripath amps and even some DIY designs have already used air core inductors for some time, and I assume they know what they are doing. That's one of the reasons I went this route.

I don't know how much heat it dissipates, since I never touched them. And I am kind of afraid I will break something, even though I made the amp. But I don't think it will get hot.
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Old 27th January 2007, 04:01 AM   #5
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cotdt, can you please post the part number for the 11uH Jantzens. I can't seem to find it on their site.

Thanks
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Old 27th January 2007, 04:15 AM   #6
cotdt is offline cotdt  United States
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I don't know the part number, but they are $6.88 each and come in 14AWG. I think there are other sizes too. You can email them and they will know.
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Old 27th January 2007, 08:14 AM   #7
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Hi.

Good to see that somebody finally confirms my air-foil-coil findings I mentioned in the output inductor thread some time ago.

You might want to have a look at the Mundorf foil coils.
They run at around 10$ each. You just order 11uH values by E-mail. They'll customize them without extra charge.

Cheers
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Old 27th January 2007, 09:01 AM   #8
Pano is online now Pano  United States
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I would be vary careful with aircore, especialy foil types. The make very good radio transmitting antennas! On the higher power amps like the amp 5, you've got a little 750 KHz transmitter going there.

All sorts of things can pick up that signal. Your input wires, pot, input caps, etc.
I does not sound nice. Tends to "sour" the music.

Aircore are nice because they are very linear, but yo have to pay attention notto get the RF back into your input cicuit. And with hihger power, you might be transmitting into your preamp, DAC or CDP if you're not careful.
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Old 27th January 2007, 11:20 AM   #9
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I run them with a 2020 at not more then 5-7W.
All coils are seperately shielded.

On high power outputs, that's a different story of course.
Though it seems that the air coils are used up to 50W applications
these days.

Cheers
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Old 27th January 2007, 01:11 PM   #10
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Quote:
Originally posted by panomaniac
I would be vary careful with aircore, especialy foil types. The make very good radio transmitting antennas! On the higher power amps like the amp 5, you've got a little 750 KHz transmitter going there.

All sorts of things can pick up that signal. Your input wires, pot, input caps, etc.
I does not sound nice. Tends to "sour" the music.

Aircore are nice because they are very linear, but yo have to pay attention notto get the RF back into your input cicuit. And with hihger power, you might be transmitting into your preamp, DAC or CDP if you're not careful.
If I can manage to get a hold of a pair I plan on trying them out on my AMP1-B. I also plan on making little grounded RF cages to fit around them.
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