air core inductors in uk

[lufbramatt]

hi guys
although i have wound the inductors for my xt25/pl18 project myself with some nice thick enamelled copper from wires.co.uk, i am about to embark on a 3 way floorstander for my dad which has a quite complicated crossover (the sp38 from troels gravesen, am waiting for him to finish and fine tune them and report back on his website, they look as if they should be really good) and really dont fancy winding all the inductors myself.
I was wondering where all the UK based diy'ers get their air cored inductors from? the ones i have found seem to have a dc resisitance that is was to high.
cheers,
matt.

[ShinOBIWAN]

Naff all selection in the UK I'm afraid.

Sure you can get air cored from places like Wilmslow, Falcon and a few others but they are merly adequate.

Personally, and when the project calls for it, I import Goertz/Alphacore Copper foil inductors from Speakercity in the US. Or sometimes from Solen. Not cheap but certainly better than the stuff over here.

[lufbramatt]

ok cheers, that was pretty much the conclusion i was coming to.

looks like im gonna be winding my own again, just have to make a better winding jig this time

[lufbramatt]

hi again- looks like the sp38 3 way speaker from troels gravesen may well be going ahead, but still no luck on finding decent inductors over here.

I see so many members with a little union jack under their nick on these boards- surely some of you must have bought inductors from somewhere over here?

cheers again, matt w.

[Puggie]

big coil of wire and a low speed lathe, then dip 'em in polyester resin to prevent buzzing.

[johninCR]

Puggie, thanks for that resin tip. What causes buzzing?

I just roll mine up on an aluminum can, slip the cable ties on after the desired # of turns, then crush the can to get it off. Plastic bottles work the same way for smaller diameters. It may be low tech but it seems to work well without being too time consuming.

[lufbramatt]

yeah i have used a simailar technique to wind the large inductors for my current project, and it absolutely killed my fingers!

i used one of the online calculators to work out the number of turns, but am not 100% sure how accurate they are. Also i found it very hard to keep track of the number of turns on each inductor as i was winding them. mine are both the same size, and weigh the same amount so i assume they are pretty well matched. I cant hear any difference between the 2 speakers, although at the mo i am not in a position to do proper freqency sweeps and record results.

What is the best way of measuring them to make sure they are correct? put them in series with a cap of known value and find the resonant freqency?

are the values particularly critical to get 100% spot on?

comments appreciated.

[richie00boy]

You haven't measured them?!!! Best way is to invest in an LCR meter, or make up a potential divider with a resistor and the inductor fed from an AC source.

[lufbramatt]

no, they havent ben measured yet due to they project being put on hold for a few months while i finish off uni, the amount of coursework i have at the moment is rediculous. But the crossovers are in a separate box at the bottom of my hifi rack so i can get at the components very easily- being my first project i knew they would probably need tweaking. The speakers are nowhere near being finished, and both need painting too.

what is a decent LCR meter and how much £ am i looking at? I have looked on the CPC website, the ones they have dont seem to be very accurate.

the potential divider method seems pretty simple, ill try it when im back at home.

cheers.

[Puggie]

Buzzing is caused because a coil with current passing through it is akin to an electromagnet, with AC you are re magnetizing it alternate ways regularly, the magnetism causes toe coils to attract and not attract eachother which can cause movement and noise (not a lot mind but if you ever notice it, it will annoy the hell out of you!). Fibreglassing resin just holds them all together nicely.