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Old 31st August 2004, 10:59 AM   #1
Oil is offline Oil  United Kingdom
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Default sourcing/building chokes

After looking at the chokes available at parts express, the best they have are 14 gauge (~2.08mm) chokes - I was looking at specifically the 2.2mH one - It is extortionate to get this shipped to the UK, and the closest I can find ANYWHERE (and i have searched everywhere..) are these

http://www.1st-4-audio.com/store/product.asp?P_ID=46

which are 1.4mm (~15/16 gauge).

So i thaught of making my own. I checked to find i can only obtain 1.5mm dia. wire easily - and found that it is only rated to 2.74A - In the aleph 5 power supply, this would mean 34 * 2.74 = 93.16W for each rail giving a total of 186w maximum per channel - way under the 300W i anticipate the amp to need.

so my question is, are the 14 gauge chokes just being overworked (i presume they would just run hot) or are they genuinely working within operating requirements. And also, any input on making my own chokes would be appreciated.

Thanks!

EDIT: Update - I have just found some 14 gauge wire, my questions still stand with the ratings etc.. - also, i got the 300w figure from a aleph 5 overview site - i took it as per channel, is it for both channels?
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Old 31st August 2004, 11:26 AM   #2
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look in the yellow pages for firms who refurbish eletric motors, they could provide you the right gauge at a fraction of the cost
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Old 31st August 2004, 12:42 PM   #3
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Oil,

the 300 watts is for two channels. I use four intertechnik 1.4mm/2.2mH aircoils in mine (340 watts/ two channels) for quite a while now without any problem. They weren´t even expensive!

William
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Old 1st September 2004, 03:30 AM   #4
Magura is offline Magura  Denmark
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Look up the shavano music inductor calculator.

Just run 2* 1.5 wire, calculate what cross section it translates to and wind it like if it was a single wire.

Magura
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Old 1st September 2004, 07:12 AM   #5
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If you want a wide range of wire by mail order in the UK, I suggest you have a look at www.wires.co.uk
They stock enamelled copper wire up to 5mm diameter!
(Plus lots of other useful wire)
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Old 1st September 2004, 07:14 PM   #6
Oil is offline Oil  United Kingdom
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thanks! decided on the intertechnik ones for simplicity
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Old 5th September 2004, 06:00 PM   #7
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If you can get your hands on them, large powdered iron chokes will work very well for a 60Hz LC filter, especially at the current levels required for a class A amplifier. They are less expensive and much easier to come by than silicon steel C cores, and easier to work with than laminations. Check micrometals.com to see what is available and for some application notes. I would recommend the larger E cores in 26 material. Micrometals may be nice enough to sample a few, but the parts can also be had from distributors like Lodestone Pacific and Amidon Associates.
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Old 5th September 2004, 08:32 PM   #8
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Subject: RE: Price and availability


I emailed Jim Smolik at ERSE for a price on the 12 guage item


ESQ55-12-2000 2.00 mh 0.061DCR

They advised a minimum order of 25 pieces and $250 dollars.

Perhaps we could arrange a group buy. I understand Passlabs uses these or similar ERSE chokes.

macka
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Old 6th September 2004, 05:39 PM   #9
Bakmeel is offline Bakmeel  Netherlands
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Default Home Wound

Why not wind your own?

This is a link to a very nice inductor calculator: http://www.lalena.com/audio/calculator/inductor/

Then do some yellow-pages work to find a transformer manufacturer and call them if they have some transformer wire for surplus. I was able to buy 300m 12-gauge wire for just 20 euros. They let me have it for just the plain copper price, because its useless for them.

Then make a wooden spool to wind your coil using a battery-powered drill - but don't lose count!

You can make any coil you like!
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Old 6th September 2004, 06:15 PM   #10
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Air core coils require a lot of turns, though they have the advantage that you cannot possibly saturate them. They will tend to spray flux around, so there may be a noise problem unless they are placed away from sensitive circuitry. Any inductor with a permeable core will have a lower DCR and fewer turns, along with a smaller size. As I mentioned in a previous post, powdered iron is a reasonable compromise as core material for inductors up to a few tens of millihenries. Because of its distributed gap. powdered iron is difficult to saturate fully, unlike ferrite and steel, which tend to saturate all at once. Using a toroidal core will help to greatly reduce stray flux.
I am running a bipolar power supply bench setup with a pair of inductors made with stacked powdered iron toroids. They are approximately fist-sized and are 20mH each, wound with 18AWG wire. Temperature rise at 4A load each side is negligable, and with one 68kuF capacitor per side, the ripple is around 100mV p-p at 4A load. This setup will eventually power my first class A amplifier. After this test, I am far more worried about building the case and heat sinks than I am about the power supply....
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