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.
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.
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.
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
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
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.
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.
panomaniac said: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.
soundcheck said:I replaced the Charlize Air Cores with the Mundorf Coils 6 month
ago!
Resolution clearly increased in the upper range.
The only problem with the Mundorfs: They are bigger than the
air cores of DIY-paradise.
That's why I mounted them underneath the board!
Cheers
So what size do these foils end up at Soundcheck?
Did you order from Mundorf direct?
Lostcause said:
25mm in diameter and 40mm tall.
I ordered directly from Mundorf.
Just tell them that you'll use them as output filter for a digital
amp. They'll know what you're talking about.
The coil comes with a wooden core. The foil sits extremely tight
on a wooden body.
I think that is one reason why it's better then the other air-cores around. It is much less sensitive to vibrations.
Cheers
OK,
what i understand is :
- An air inductor is linear because the core itself is linear (the air) vs a solid core (hysteresis).
- The air coils is working quite well for low power amplifier (2-10W) but need to be shielded in a faraday enclosure to avoid EMI troubles in the case of 50W amplifiers.
- The chip itself needs to be shielded too (reduction of distorsion and background noise) in high power applications.
The output coils are then the critical part of the Class D amplifier and there are no immediate answer to all applications. I read that some of you don't have any troubles with 50W amplifiers and air coils : the way to go is maybe to enclose the entire board and connect the coil in another enclosure as close as possible of the first one.
am I right ?
what i understand is :
- An air inductor is linear because the core itself is linear (the air) vs a solid core (hysteresis).
- The air coils is working quite well for low power amplifier (2-10W) but need to be shielded in a faraday enclosure to avoid EMI troubles in the case of 50W amplifiers.
- The chip itself needs to be shielded too (reduction of distorsion and background noise) in high power applications.
The output coils are then the critical part of the Class D amplifier and there are no immediate answer to all applications. I read that some of you don't have any troubles with 50W amplifiers and air coils : the way to go is maybe to enclose the entire board and connect the coil in another enclosure as close as possible of the first one.
am I right ?
Commercial Tripath amps with 300W per channel somehow get away with using air coils, so I don't know how serious the problem is. Not a problem in my case, though. Hysterisis isn't really a problem with the officially specified iron-core inductor, but for some unknown reason it sounds bad. I haven't read any good explanations as to why using better inductors can make the sound better, but it does. Maybe the extremely high frequencies involved have effects that are not easy to predict. The difference is massive, bigger than changing capacitors.
The Jantzen copper foils and Mundorfs look to be about the same. They have similar designs and both use a wood center core. So take your pick, and go with the cheapest. The 14GA Jantzen is $6.88 each from parts express.
The Jantzen copper foils and Mundorfs look to be about the same. They have similar designs and both use a wood center core. So take your pick, and go with the cheapest. The 14GA Jantzen is $6.88 each from parts express.
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