anonymous ebay AMT tweeters?

[ericj]

I've noticed recently some smallish, cheapish, no-name AMT / Heil type tweeters on ebay, sold by sellers in china.

Has anybody tried these out?

I mean like item 261599865615

 

[Tape Echo]

Two recent threads do touch upon this trend:

http://www.diyaudio.com/forums/planars-exotics/257604-amts-minimal-2-way-test.html

http://www.diyaudio.com/forums/planars-exotics/260537-has-anyone-tried-chinese-amt.html

 

[ericj]

2nd thread there does look like they identified the tweeter, or at least identified what it is trying to look like. 5k sounds about right for a driver that small.

 

[Greebster]

Great little (super) tweeter crossed above 5k. Can be used lower (3.5k) if mated with a waveguide. This would also reduce the low end distortion. Passive filters/ active eq to wring out the flattest response.

 

[ericj]

Yeah, I'm considering getting a couple and making them little supertweeter stands, crossed over good and high, for kicks.

 

[Greebster]

Above 7kHz would be super. They are smaller than you think. If ambitious, have slots cut the same on the back plate and make it full dipole. Reduces distortion by ~20dB 😉

 

[Pravsovet]

Are you sure you can do it from the dipole? There may be a magnet under the back cover. If the magnets on the sides, it is good. I'm looking for a cheap dipole Heil.

 

[Greebster]

I'm assuming the magnets are placed the same as the rt4001. This would place the magnets across the back directly behind the metal parts of the aperature plate between the slots. The rt4001 has 4 magnets. Nothing on the top or bottom. Would be no problem for a machinist.

 

[ericj]

No problem for a guy with a compound table on a drill press either.

Not that i have one.

They might be cheap enough to free-hand it with a dremel tho.

or more likely lay out a pattern in sharpie, drill it out in a press, and clean it up with a dremel.

 

[Greebster]

Skills like a jewler. Can see using a drill press and the filing away the remaining ridges working. Free hand not possible with power tools. But if friction isn't kept in check, degaussing the magnets will. Neo's have a conciderably lower operating temp range. The latest, best are N52's eg 52c, but these are probably made of N45 or a little lower.

Friend built a nice ducted fanjet, little bat out of hell fast (~210kmh) after several flights over two weekends realised it wasn't going as fast, made a few measurements. He was driving that little 1oz 3phase motor rated for ~300w @ 525w. Cooked the magnets causing a massive increase in current consumption. Before new neo's were installed it was drawing around 1kw and 1/3rd the actual torque output.

 

[ericj]

I didn't assume that the magnets would be attached while working it.

But i don't know how they are constructed.

I freehand small objects with cutoff wheels pretty regularly. Granted not all of them turn out perfectly.

it may be sufficient to perforate the back with neatly drilled holes.

 

[Greebster]

Completely disassembled mine today. Between the outer front and back plate is a magnet steel ring that completes the motor circuit. Inside there are two plastic frames, one hold the magnets (4) in alignment to the back plate and the other holds the ribbon. Only the magnet frame is lightely glued and easily lifted away from the backplate with a razor. Between the magnet gaps are felt pads. Again not glued in place and easily lifted out. I used a dental pick. Magnets are not glued, but may require prying them side to side to break free. Easily done.

After this it would be easy to align the registration and either drilled out or machined. Reassemble without felt pads.

It's late so will post pics tomorrow, after coffee 🙂

P.S. wife said, Why did we pay $90 for each when you are just going to change them?! I responded, When have I done any different? 😀