Coil values on AR3a crossover ??

[Guest Danlaet]

Hi !

I'm new on this forum, I'm french and I just have purchased a pair of AR3a speakers.

Let me tell you about them : Old Alnico woofers, AR3 crossovers, but AR3a midranges and tweeters. So I want to rebuilt AR3a crossovers for them.

I have the capacitors values, but for the coils value it seem to be more complex : I have seen differents things :

1) 0.75 mH - 0.35 mH - 4.5 mH, here : http://www.humanspeakers.com/o/ar/3a.htm

2) 0.044 mH - 0.35 mH - 2.85 mH or 1.88 mH (for the Alnico woofers ones).

So is there someone here to give me some light please ? I have made a mail to Layne Audio, but no answer till now.

And a last question : what is the value of the bass coil on the AR3 crossover (perhaps I could use them in my new crossovers ?).

Thanks to have read my catastrophic english.

Daniel

[RoyC]

Welcome to the forum, Daniel.

I think Layne Audio keeps the website on the web just to annoy people, and I would disregard the humanspeakers restoration. You have arrived at the best place for AR information.

The correct coil values for the AR-3a are .044mh (in series with mid), .88mh (parallel with mid), and 2.85mh (series with ceramic woofer) or 1.88mh (series with alnico woofer).

Attached are a couple of diagrams for your reference.

Although the notes show the original 50v electrolytic capacitors and 17ga coils, 100v+ caps should be used as replacements, and 18ga coils will work satisfactorily if originals cannot be obtained. Later AR coils of the same values (ie the #9/2.85mh coil used for the ceramic woofer) were changed to 18ga in the early 80's.

Use the "Search" function and the Library for much additional information.

Roy

[Guest hilltroll67]

I agree with Roy (I agree with Roy most of the time). Regarding the Humanspeakers guy, when I read all of his site I realized that he has limited knowledge of AR speakers. I freely admit that I based the physical layout of my AR94Sx crossover on his '6 inches between inductors' dictum, but hey, there's plenty of room in there.

Bob

[Guest Danlaet]

Thanks for your answers, loud and clear !!

I have found a diagram in which this is not a 0.88mH, but a 0.35 one :

http://www.classicspeakerpages.net/dc/user_files/2395.jpg

But perhaps it's another hazardous change.

And a question again : the potentiometers have been replaced by 8 ohms ones.

16 ohms potentiometers seem to be impossible to find. Is it a problem and if it is, do you think I can use a 8 ohms resistance, or two 4 ohms resistances ?

Daniel

PS : I don't understand "17Ga coils".

[RoyC]

Daniel,

>I have found a diagram in which this is not a 0.88mH, but a

>0.35 one :

I have seen that one as well, and it is misleading. AR's #4 coil is .88mh. Of the many 3a's we have compiled data on, not one has ever had anything but the #4/.88mh coil in the midrange circuit.

>And a question again : the potentiometers have been replaced

>by 8 ohms ones.

>16 ohms potentiometers seem to be impossible to find. Is it a

>problem and if it is, do you think I can use a 8 ohms

>resistance, or two 4 ohms resistances ?

I'm guessing your replacement level controls are common 8 ohm l-pads. Potentiometers and l-pads behave differently, so a 16 ohm potentiometer and a 16 ohm l-pad would not have the same effect.

Common 8 ohm l-pads are being used satisfactorily by many folks. Since they are already installed in your speakers, you might as well give them a try. If you want to get closer to the original characteristics of the original potentiometers, you can leave your l-pads installed and put a 25 ohm resistor in parallel with the tweeter and mid.

The old tweeters may actually benefit by a slight boost provided by the l-pads. The mids would probably benefit the most from the 25 ohm parallel resistor, or an original 16 ohm pot.

If you want an "authentic" restoration, there are forum members, including myself, that have refurbished pots you could purchase...but I would try your installed l-pads first.

>PS : I don't understand "17Ga coils".

The "ga" (short for "gauge") refers to the inductor coil magnetic wire thickness, with the associated overall resistance in the circuit being an important factor. The lower the number, the thicker the wire, and lower the resistance. The 17 gauge coil wire originally used in AR coils is pretty scarce these days.

Roy

[dynaco_dan]

>If you want an "authentic" restoration, there are

>forum members, including myself, that have refurbished pots

>you could purchase...but I would try your installed l-pads

>first.

>

>>PS : I don't understand "17Ga coils".

>

>The "ga" (short for "gauge") refers to the

>inductor coil magnetic wire thickness, with the associated

>overall resistance in the circuit being an important factor.

>The lower the number, the thicker the wire, and lower the

>resistance. The 17 gauge coil wire originally used in AR

>coils is pretty scarce these days.

>

>Roy

Hi there;

Roy is absolutely correct.

I am going to give you an example, not an exact example, just a close sample.

You can buy 10, 12, 14, 16, 18 and I believe 20 guage coils.

They each have a specified overall resistance.

There is a coil chart that I believe Tom Tyson downloaded to this site.

AR, for whatever reason, used 17 guage wire, for their coils.

The coils each had a specific resistance which is different than 16 or 18 guage.

You may read in here somewhere, if you want to approximate an AR coil, then buy a, 16 or 18 guage, the higher resistance, and remove a few wraps.

This would be done with the higher resistance version only.

[Guest Danlaet]

Ok, I think I understand. Technical english is sometimes hard to understand for me but I have my dictionnary in my left hand. 17Ga correspond at a determined resistance ? (Yes ? / No ?) But which resistance, in ohms ? Surely I'm completely out...

Not sure to have l-pads and no pots, don't know. My electronic knowledges are very poor.

I have good news : perhaps I will have in a few days / weeks a pair of original AR3a crossovers, I learned that just this morning. But nothing is really sure.

When I read what I wrote I'm surprised that you can undestand what I say.

Daniel

[dynaco_dan]

>Ok, I think I understand. Technical english is sometimes hard

>to understand for me but I have my dictionnary in my left

>hand. 17Ga correspond at a determined resistance ? (Yes ? / No

>?) But which resistance, in ohms ? Surely I'm completely

>out...

>

>Not sure to have l-pads and no pots, don't know. My electronic

>knowledges are very poor.

>

>I have good news : perhaps I will have in a few days / weeks a

>pair of original AR3a crossovers, I learned that just this

>morning. But nothing is really sure.

>

>When I read what I wrote I'm surprised that you can undestand

>what I say.

>

>Daniel

>

Hi again, Daniel;

I'm Scottish, Irish, English and born in Vancouver BC.

I grew up with mostly Italians, a few Chinese, and a blend of many other cultures.

This web site is available to anyone worldwide, who make the effort to ask or answer a question.

You may not understand the, 17G, (guage), but, you are not the only person.

The wire used for a coil is bought from their supplier in large rolls of perhaps thousands of feet or metres long.

They would specify the diameter of the wire in 0.001" or Centimeters.

This wire has a shellac or other clear or slightly copper coloured insulation, so that the wire can be wrapped around a form and create a coil.

There is special coil winding machines, similar to a fly-fishing reel that will wind, usually on a plastic spool, a certain calaulated length as it winds.

The more expensive companies will test and identify the value of inductance and resistance to a fine value for each coil.

For the cost's involved, making one or two custom values, we may wish to buy the next value up in size and remove a few turns, by guess, by golly.

The wire, when insulated, only passes current at each end, unless there is a cut or nick in between.

Perhaps when AR used 17 guage wire coils, it may have been a common size wire.

Today it is, I believe, perhaps only available for OEM's in large quantities.

10, 12, 14, 16, 18, 20, up to at least 32 guage wire is readily available at most all electronic shops as, also know as "magnet wire" in the electronics field.

Please remember that 10 guage is closer to 1/8" or .125" in diameter.

32 guage is closer to the diameter of a human hair.

[RoyC]

Daniel,

Converting your existing AR-3 crossover to a 3a crossover will not be a simple job. Everything will need to be replaced, and additional components will need to be added. If you are able to obtain the AR-3a's you mentioned, it will be much easier to understand.

When you decide to get the parts for your project, I recommend simply buying used AR coils. They can still be found here and on Ebay.

Unless you have a meter to measure and adjust new coils, I would not advise buying new. IF you do buy new coils, "18 gauge" and "air core" are all you need to know. They are very easy to find, and not very expensive.

Try exploring speaker building websites, or a website like www.partsexpress.com. You will be able get a better idea of what we are talking about by going to the crossover parts section of the "Speaker Building" section of the website.

Roy

[Guest Danlaet]

Ok, I have found explainations and formula :

Diameter = 0,32" / 2^(-G/6)

So AWG18=diameter 0.045" = 0.1 cm

SO here in France we say, I think, for AWG18, 10/10.

Yeah !!! The things are now clear, thanks !!

I agree whith you, the best is to find original cores. No meter to measure and adjust new coils.

Many things in partexpress.com, thanks.

Today I have to refoam an AR3 woofer.

SO go on...

Daniel

[dynaco_dan]

Hi again Daniel;

I should have looked up Tom Tyson's great AR coil sheet that he downloaded here dated 5/8/74 drawing #102014.

I quickly found a bad copy I had printed out.

Using the search feature of this site, I typed in 934.JPG, in the AR only forum, which was printed on the bottom of my bad sheet, at least.

My bad sheet was printing from the site to my printer.

By downloading to my computer and printing later, I found no problem with my printed copy.

The search pulled up the original and only topic started by, Tom Tyson, Jan 31/06, great going Tom.

Now to the point of my re-writing here, Daniel.

An AR-3A coil, as per sheet, has a #4 coil with 200 1/2 turns +/- 2 turns of 17 guage wire, which equal's 0.880 mH +/- 0.060 mH and has a resistance of 0.35 ohms.

I hope this does not confuse you any more than I have already.