ever built an air core inductor?

Shopping for inductors at Madisound:
http://www.madisound.com/inductors.html
Thinking, "hmmm, these look like wire wound on spools. I can do this myself right?"

Found this calculator:
http://colomar.com/Shavano/inductor_info.html

Is there anything else to it? Anyone tried it and want to talk me out of it?
Is there an easy way to measure henries? To see if I did it right?

Thanks for any insight, Kato

Capacitance will get ya on a spool of wire.
Most air cores are too low in mH for audio.
Unless it's a speak crossover, as per Mr. Foote

Yeah, above a mH or two, air-core becomes impractical.

I used to wind my own air-core solenoids for RF use, with inductances in the 100s of microhenries. I wound them on Mom's discarded thread bobbins :grin:

Here are $183.00 air coil inductors.

http://www.northcreekmusic.com/NorthCreekCoilPrices.PDF

They make them up to 40mH and 8 guage wire. :shock: :?

I don't like passive crossovers anyway lol.

Kiira

Passive crossovers are fine. Audiophiles just have a way of making everything really anal-retentive and stupid, that's all.

Roger, I used to brush my finished inductors with "coil dope." And yes, I liked it mainly because of the name (although it did happen to work very well).

One thing to keep in mind when winding your own coils is to keep the cross section of the winding equal - as an example, if you were to cut a coil down the middle and view the cross section of the winding, it should be as high top to bottom as it is wide. Check this out:
http://colomar.com/Shavano/inductor_info.html
http://sound.westhost.com/lr-passive.htm

I have had the crazy idea of doing an air-core inductor passive EQ someday. :twisted:

The last time I calculated, some of the coild ended up weighing several kilograms - these things would need THICK wire to end up with decent resistance.

I still like the idea. A passive EQ that would probably be at least 6u high, have only few bands and the weight around 20-30 kg. :razz:

air-core inductor passive EQ

Click to expand...

Problem is that you run into destructive parasitic capacitances long before you have anything in a usefull size for 600Ohms work.

workaround:

Run the filter sections at ultra-low impedance, driven from an opamp, possibly with power boosting and step-down transformer. At very-low impedances, you can do with low inductances (think speaker crossovers again) - but you will need large capacitances. Well, these days large capacitors are not nery expensive.. :razz:

(Think of ManleyMP - why do you think they have these opamps driving the filters, instead of making it a real tube eq..?)

Jakob E.

[quote author="Viitalahde"]I have had the crazy idea of doing an air-core inductor passive EQ someday. :twisted:

The last time I calculated, some of the coild ended up weighing several kilograms - these things would need THICK wire to end up with decent resistance.

I still like the idea. A passive EQ that would probably be at least 6u high, have only few bands and the weight around 20-30 kg. :razz:[/quote]

You're really quite mad you know. Oh wait you're from Finland.. never mind. :razz:

That link up there sells huge inductors made out of huge wire, for huge prices. They're over six inches in diameter. Jaakko that would be a huuuuge EQ can't wait to see it! :roll: The thing is it would impress clients like crazy I bet!

I've started on the passive EQ designed by NYDave of the well known New York Daves. Mr. Wilco decided he liked me after all and sent me some BSL inductors... I only asked for seven of them yeesh. Mr. Onsemi has sent me $200 worth of expensive output transisters (I can put in a good word for you if you need some). I wish Onsemi made switches lol.

I'm building the NYD passive on a turret board with solder terminal switches. I have greyhills for the band selection switches because I got a great deal on some but I can't find anything other than Alphas or Lorlins for the 12 pole switches and the Alphas wear out and I don't like the Lorlins. CTS has some nice ones I really like BUT their shorting switches for $8 are 11 pole not 12.... only the BBM have 12 poles. wtf? :sad:

There are lots of good quality surplus switches on ebay from Russia, I have a few but I hardly ever see MBB ones. I'm trying to concoct some scheme to use BBM switches where MMB are needed. The problem is the period when there is no continuity during the "break". I've considered modifying the wiper on the ones where it is accessable. Yech. The only other thing I have thought of is a manual switch to shunt the rotary switch to ground with a suitable resistor during the breaking before making phase. That's relatively nutso as well, but it would work.

Kiira

I'm trying to concoct some scheme to use BBM switches where MMB are needed. The problem is the period when there is no continuity during the "break".

Click to expand...

In the good old days it was common to shunt every switch position with a high-ohmic resistor to get rid of trouble like scratching at intermittent switching. Might work for you..

A passive EQ that would probably be at least 6u high, have only few bands and the weight around 20-30 kg

Click to expand...

K&H UE-100

Jakob E.

[quote author="gyraf"]

I'm trying to concoct some scheme to use BBM switches where MMB are needed. The problem is the period when there is no continuity during the "break".

Click to expand...

In the good old days it was common to shunt every switch position with a high-ohmic resistor to get rid of trouble like scratching at intermittent switching. Might work for you..
[/quote]

Well you would just need one resistor from the wiper to ground I think and that will work on attenuators if you know what impedance you want the stage to see... that's how I understand it anyway. But the values of the series attenuator will vary if the shunt is used - I have a spreadsheet for that. So if I just use like a 1M to ground would that mess up the calculations Dave did for the attenutaor in his desighn... it seems like it would. argh.

Kiira

[quote author="gyraf"](Think of ManleyMP - why do you think they have these opamps driving the filters, instead of making it a real tube eq..?)[/quote]

Now that has nothing to do with the cheap-o high DCR coils. It's about optimizing the sound for the carefully selected inductors. :razz:

Oh yeah, I did have the idea to run it at extremely low impedance.

Yeah. :twisted: Power amp front end!

Kiira, try the BBM switches if you want... The output of the switches is already shunted by the 500-600 ohm load that the EQ needs to work into--so there's no point in adding additional shunt resistors. Both input and output sides of the switch will already be "tied down."

[quote author="NewYorkDave"]Kiira, try the BBM switches if you want... The output of the switches is already shunted by the 500-600 ohm load that the EQ needs to work into--so there's no point in adding additional shunt resistors. Both input and output sides of the switch will already be "tied down."[/quote]

Ok. Rawk. I can start soldering tomorrow then. Yay.

thanks!

Kiira

What mag wire coating is appropriate for speaker crossovers?
The Shavano site says:

Use transformer wire that has a lacquer finish. Do not use wire that has plastic sheathing around it...

Click to expand...

Check out the drop down list of available coatings:
http://www.mwswire.com/awgsearch1.asp

It's kinda mind-boggling, and of course, none of them say "lacquer."

[quote author="RogerFoote"]
Don't know what the coatings are now, but on transformers I have seen in the last 20 years, definately not lacquer.[/quote]

These are their available options:



Which of these says, "laquer, not plastic sheathing" to you?

I'm guessing "polyurethane?"
(or even "plain enamel.")

coatings don't matter at these temps, plus, you want something you can tin without a blow torch.

here is a 1 mH air core speak crossover inductor and
a do-it-yourself rf inductor, you trim off as much henries as you want from 76 uH, and then fire up your viking xtal for 10 M dot dit dot action.

speaker guy is a Grand Transformer
#40-194 Grand Haven, Michigan.

I found several suppliers who don't mention a coating choice.
That way I know my choice is correct.

bulkwire.com
alltronics.com
surplussales.com

all sell just plain old "magnet wire." Makes the job easy...