8 Ohms tweeter, Pots or L-Pads, AR-3a Limited

[mluong303]

Carlos at AB tech is telling the Truth. Even way back to 1990, AB Tech had servicing blown AR 8 Ohms tweeters that way. It is a bit strange but this is the only go around way to fix the problem with genuin AR tweeters. The replacement AR-3a tweeter cost $62.50 at the time and not too many people will pay that price to fix their AR-2ax or AR-5 speakers. But for the people who own AR-3a, AR-LST or AR-9 etc., they will more likely to pay for the tweeters and get their AR speakers back to service again. That is why AB Tech have no intension to order the 8 Ohms version. Each batch of order has to be minimum of 2500 units or so.

In 1992 at the time AR was still in MA. The US made 3/4" cloth dome with Ferro fluid cool tweeter were running out of stock and AR started to contract Tonegen in Japan to build the AR-3a drivers. It all started with 500 pairs of custom order AR-3a limited speakers which were ordered by Ming Fat Company of Hong Kong, the exclusive AR importer in the Far East. These AR-3a speakers were distributed mainly to Hong Kong and Taiwan and some ended up in Japan. Very few AR fans in the U.S. really acknowledge about this fact. I had a hard time trying to buy a pair from AR since AR had made an agreement to ship all 500 pairs to the over sea market only. Few unassembled brand new AR-3a limited cabinets and small amount of unused AR-3a Limited crossovers later on were sold in the US market when AR moved to Benicia around 1993. Alex of AB Tech and Ken Kantor are the two people who do know the existence of these AR-3a Limited speakers... The two pots were replaced with two 15W 8 Ohms L-pads. I wish Ken still remember who was in charged at the time and is there any way to locate the crossover schematic for this AR-3a Limited speaker which had slight change in Cap and Coil values to go along with the 8 Ohms L-pads. They still crossover at 575Hz and 5000 Hz. The cabinet was 3/4" MDF covered with walnut vinyl. During this time the Green Planet wave and Environmental protection issues are going on strong. The terminals opening was rounded corner rectangle instead of the round opening we are familiar with.

I strongly recommand disassemble, clean and lubricate the 4 pots rather than bypassing them. The truth of the matter is these 4 pots will allow you to fine tune the output levels of the tweeters and the midranges to a closer match. The fixed resistors will not give you this option. If you are not handy enough or just don't want to bother with the pots then you can certainly use four 8 Ohms 15W L-pads for replacement. They should be dropped in replacements with no need for any openning modification. Don't bother with the 16 Ohms or huge 50W which will be a hassel do deal with.

[Guest loudsubz]

i thought they were 15 ohm potentiometers not L-pads

nice info

thanks

[RoyC]

Well you just solved a mystery for me. Back in early '96 I purchased "factory buyout" AR3a crossovers and midranges from Parts Express. The price was right and I was curious. The crossovers are as you described them with 15 watt 8 ohm l-pads installed. AR3a is clearly stamped on them and they are the same as the original (refer to the schematic on this website) with the following differences:

-The tweeter cap is a 4mfd mylar instead of the original 6mfd electrolytic.

-The tweeter has a .16mh coil across the terminals as opposed to none in the original.

-The midrange cap is a 40mfd electrolytic instead of the original 50mfd

-The coil across the terminals is .7mh instead of the original .88mh.

-The original.5 ohm resistor wire in the mid circuit is replaced with a 22watt .5 ohm sandcast resistor.

-The woofer coil is 2.6mh instead of the original 2.85mh.

-All coils are 18ga with similar resistance values as the originals.

-All other components are the same as the original. The parallel 150mfd woofer cap (now 3 electrolytic 50's in parallel) and the .044 series midrange coil are the same.

-The mid and tweeter are wired in phase with the woofer unlike the original.

-All caps are rated 100watts instead of the original 50watts.

The changes appear to compensate for the lowering of the crossover frequency points the 8 ohm l-pads would have brought about.

The "15 ohm pots" of old actually kept the impedance of the mid and tweeter circuits low (below 4 ohms). It would be interesting to see how a 4 ohm l-pad were to work as a direct replacement for the pots without any of the above changes. 16 ohm l-pads would seem out of the question.

Roy

[mluong303]

The AR-3a Limited is the only model used 8 Ohms L-Pads. All others AR-3a speakers used 15 Ohms Pots and the AR-3a Improved used two position A B switches.

Attached is the AR-3a Limited review from Japanese Stereo Sound quartery in 1994. Very big Chinese community and Asian groups in the South East Asia love AR speakers as much as we do in the United States.

[mluong303]

These are Japanese AR-3a restoring project links.

http://www.onomichi.ne.jp/~ishii/ar3a/index2.html

http://www.onomichi.ne.jp/~ishii/ar3a/index3.html

[mluong303]

Thanks, Roy for the info. The numbers as discribed sound just right. Can you translate your discription into schematic drawing for Us, Please.

Here is the link to see the AR-3a Limited speakers in color.

http://www.accuphase.ru/kogerer/ar-3a.html

[RoyC]

Your welcome!

Please note a correction..All the caps are 100v (as compared to 50v in the old speakers) not "watts". It was too late to correct the mistake when I caught it.

I was using old notes and have no schematic drawn. The crossovers are currently buried in a pair of speakers. Take a look at the Ar3a schematics on this website and you will see all the counterparts to the new components. Disregard the pots. The drivers are connected to the l-pads in the modern day conventional way and all series components are on the positive side of the input. All drivers have there own wire leads (no common yellow as in the old version) and no drivers are reversed in phase. If you have questions email me and I'll be happy to answer them if I can.

The crossovers were on printed circuit boards with the 2 larger coils (.7mh and 2.6mh) for each on a separate piece of masonite. The binding posts (4 of them) are gold plated with gold jumper plates to separate the woofer from the mid and tweeter. I do not recall, nor could I easily see, how the woofer circuit was separated on the circuit board.

The irony is that the small l-pads which are soldered directly to the circuit board are now getting scratchy!! They look to be more difficult to replace than the old pots! The level controls are a pain no matter what era AR3a we are dealing with.

Thanks for the insight and pictures! It would be interesting to hear Ken K.'s take on these speakers and the influence, if any, on the AR 303 project.

Roy

[Pete B]

>The crossovers are currently buried in a pair of speakers. Take a

>look at the Ar3a schematics on this website and you will see

>all the counterparts to the new components. Disregard the

>pots. The drivers are connected to the l-pads in the modern

>day conventional way and all series components are on the

>positive side of the input. All drivers have there own wire

>leads (no common yellow as in the old version) and no drivers

>are reversed in phase.

>Roy

Thanks Roy for all this info, the big question is how this version sound? Any major differences?

[RoyC]

>Thanks Roy for all this info, the big question is how this

>version sound? Any major differences?

Unfortunately I have not tried them yet with original AR3a drivers. I used them with Tonegan replacements. I had purchased the "factory buyout" mids at the same time as the crossovers for $20 each and decided to build "modern AR3a's" by puchasing the other drivers' new counterparts. Of course I just found out above that I had actually built "Limiteds". They have a nice sound but do not sound like the original AR3a's. I believe, however, that the difference has more to do with the replacement drivers I used. The Tonegan woofer does not have that low bass growl of the older looser suspension woofers, and the tweeter is completely different as discussed on the 3a tweeter thread. My impression is that the mid response is more detailed and open but the bass is not as satisfying..more mid bass and less low bass when compared to the originals.

According to mluong303 who informed me by email that he had owned a pair of "Limited's", they sound more like AR11's than AR3a's. Maybe he can add to this.

I plan to build this crossover into a 35 year old pair of AR3a's with all original drivers in the not too distant future and will report back..

Roy

[RoyC]

I should add that early on I reversed the mid phase relative to the tweeter and woofer and found it to be preferable...not as forward.

[Pete B]

"They have a nice sound but do not sound like the original AR3a's. I believe, however, that the difference has more to do with the replacement drivers I used. The Tonegan woofer does not have that low bass growl of the older looser suspension woofers, and the tweeter is completely different as discussed on the 3a tweeter thread. My impression is that the mid response is more detailed and open but the bass is not as satisfying..more mid bass and less low bass when compared to the originals. "

I follow and what you say makes sense. We can probably figure out the woofer differences if you have T&S parameters for both. It sounds like they might have a bit too much damping which results in a lower Qtc. You can try adding .5 to 1 ohms in series with the woofer to reduce the electrical damping, and push back or remove some of the acoustical damping in the enclosure. Do you know if they have about the same in box resonance frequency, Fc?

I like to put the two systems side by side and wire it so that the mid and tweeter from one system are always used, then switch just the driver that your trying to duplicate, in this case the woofer. This helps to narrows down the differences to try and pin point the cause.

[mluong303]

Hi, Roy,

I said "Please don't bother to take the crossover out of your speaker for pictures. I did owned a set before and know exactly what they look like." I mean a set of crossovers not the factory made AR-3a Limited speakers. I did encounter the actual AR-3a Limited speakers in Hong Kong used market and almost bought a pair back to the U.S. in 1996 but the Air Freight scared me off and at that time I already had my own pair. I had custom built an mirror imaged pair of AR-3a Limited using brand new AR-Limited crossovers and Tonegen drivers from AB Tech in 1994 after I found out I will not be able to buy a new pair of AR-3a Limited speakers from AR... That is how I know what they sound like. The custom built AR-3a Limited of mine was sold about 2 years ago!

The AR-3a Limited has a closer sound quality to the AR-11 than the original AR-3a due to the more forward tweeters and stiffer suspension spider woofers. The bass still very tight as the AR 12" woofers should be in my custom built pair eventhough they are a bit different compare to the original AR-3a when compare next to each other. Over all the Tonegen tweeter, midrange and woofer combo should work better with the Limited crossover since that was what AR tested the AR-3a Limited crossover to finalized the design and put in production. It certainly won't hurt to try out the possibility and hear for yourself with the original AR-3a foam surround woofer if that is what you prefer. It all comes down to personal peference and believe after all.

If you take a DC resistance reading of the tweeter, midrange and woofer pair and if they are in close matched than you may want to try to bypass the pots or L-Pads altogether simply because your living area sounds like the humidity condition is not very well controled. I said don't bypass them in the post because old drivers are very unmatched in voice coils resistence due to age and sometimes misused which need all the helps of the pots to tune them in balance.

[RoyC]

Thanks for the tips Pete...Unfortunately I have no measurements or woofer specs. I originally plugged the Tonegan woofers into old 3a's. That's when I first found that they are different animals. For one thing, as with all the new 3a "replacement" drivers, they have higher sensitivity...

and I believe you are right, they apparently have different cabinet stuffing requirements. The trial and error got tedious and I finally gave up. I even tried larger cabinets. Thats when I built what I will now refer to as my "Limiteds".

On the other hand I have (2) 6 year old NHT1259's that have never been used..maybe its time for a new project. I took another look at your website!!

Roy

PS Forgot to mention that I did try the series resistance (.5 ohm) at one point but didn't think it made much difference.

[RoyC]

>If you take a DC resistance reading of the tweeter, midrange

>and woofer pair and if they are in close matched than you may

>want to try to bypass the pots or L-Pads altogether simply

>because your living area sounds like the humidity condition is

>not very well controled. I said don't bypass them in the post

>because old drivers are very unmatched in voice coils

>resistence due to age and sometimes misused which need all the

>helps of the pots to tune them in balance.

Hi Minh,

Its just that so many people are wrestling with corroded old pots and replacement drivers, that a couple of alternative ARish solutions would be nice to offer. Certainly any by-passing needs to provide the equivalent resistive effect within the crossover if the goal is to keep them sounding "original". Thanks for your insight and great links! I'll let you know how I make out.

Roy

[mluong303]

Other interesting info on AR-3a speakers:

http://www.arsound.com/public_html/speaker...3a/ar3atest.htm

http://www.decware.com/bbs/messages/470.html

http://murphyblaster.com/content.php?f=AR3a.html

Enjoy and Happy Holiday... )

[Pete B]

Hi Roy,

What you write makes sense. I can help if you want to nail down these diffeneces. It's easy to simulate this, and simulation matches real world very well, if we measure the T&S parameters. It's important that the drivers have approximately the same cone mass so that Fc is the same in both cases. I expected that the new motors would be stronger which is supported by their higher sensitivity. If this is true you want to add series resistance, it might take more than .5 ohms, to bring it back down and raise Qtc. Qtc will come up faster if you push the stuffing away from the driver and even remove say 10 to 25% near the woofer. I wonder how Rdc compares between the two drivers? The next detail is to make sure that the woofer loads the crossover correctly and perhaps make XO adjustments to compensate for differences in the upper range of the woofers, if there are any. It may be counter intuitive to put resistance in series with the woofer but it is the only way to clone the sound of the older woofer. There is one advantage in that for a given power level the new woofer will run cooler since some of the power goes into the resistor.

Are you planning a super AR 3a with those 1259s?

Pete

>Thanks for the tips Pete...Unfortunately I have no

>measurements or woofer specs. I originally plugged the Tonegan

>woofers into old 3a's. That's when I first found that they are

>different animals. For one thing, as with all the new 3a

>"replacement" drivers, they have higher sensitivity...

>and I believe you are right, they apparently have different

>cabinet stuffing requirements. The trial and error got

>tedious and I finally gave up. I even tried larger cabinets.

>Thats when I built what I will now refer to as my "Limiteds".

>

>

>On the other hand I have (2) 6 year old NHT1259's that have

>never been used..maybe its time for a new project. I took

>another look at your website!!

>

>Roy

>

>PS Forgot to mention that I did try the series resistance (.5

>ohm) at one point but didn't think it made much difference.

[RoyC]

Hey Pete,

I found some old notes with some measurements I made with a simple LCR meter. The Tonegan woofer was about .2ohms higher Dcr and .03mh higher inductance. There is no doubt about the substantially stiffer suspension compared to any old AR3a woofer...and who knows about the cone mass. To my ear the new raw woofer has noticably more output but less extension into the higher frequencies when compared directly to an old one. I guess the bottom line is that it wasn't quite the "drop in" replacement for the AR3a that someone "restoring" these things would have hoped for. It fits the hole....

The 11"/12" woofer was a mainstay of the AR line for many years and it was apparently altered somewhat to fit subsequent designs and handle more power. The Tonegan replacement was supposedly based on the latest incarnation...although I read a post here someplace that a fellow with AR9's didn't like them much either and went back to his re-foamed old ones. I should mention that all the "new" replacements (tweeter, mid and woofer) sound rather good together with the "Limited" crossover. I'm just nitpicking the deep, tangible, bass reponse that so many AR3a fans have come to expect at any volume.

Interestingly, I just had an old mid-60's AR3a apart which used the "original" old style cloth surround AR3 woofer (very "floppy"). The crossover was different...the woofer coil was about 1mh less at 1.9mh(I think its an AR#7 instead of the 2.85mh #9)) and there was more fiberglass stuffing in volume and weight than I've seen in later versions with the foam surround woofers. The pots were nearly 17 ohms compared to the typical 15 ohms. I previously thought those pots were only used in the 8 ohm rated AR speakers. So it appears not all our old AR3a's were created equal either!

Now about those NHT's...You guessed it. I bought them new with the intent to build a modern AR3a using AR mids and tweeters. I got sidetracked with the "limited" crossover/new AR driver project, moved to a smaller residence, didn't feel like dealing with obtaining the required larger cabinets, and forgot about them.

Roy

[Pete B]

Hi Roy,

Sounds like they got the voice coil right with your Rvc and Lvc numbers, but as you say the motor is probably stronger.

I have some idea of the 11/12" woofers that have been used, but could someone go over the evolution from the AR1, AR3a, 9, 10 and 11, what's currently available new, is there a new AB tech 11/12" is it identical to any of the production units? Is the AR 303 a good replacement, is it currently available? It would probably be good to start an AR 11/12" Woofer thread to discuss this.

Pete

[RoyC]

Its always been an odd size, fitting into a 10 1/2" hole. In the Ar1, Ar3 and AR3a, there is no room to spare relative to the cabinet molding (the reason for the 2 flat spots on the outside of the basket).

The current replacement is/was made by Tonegan in Japan, the same company that made the AR303 and NHT1259 woofers. I think I read someplace that Tonegan is no longer in business.

You're right, probably should start a new thread if we keep going...

Roy

[Pete B]

Hi Roy,

A few thoughts for what they're worth, I'd probably go with a 5 to 6.5" mid, and 1" dome with the 1259 to do an up to date 3-way. There happens to be a 1" SEAS 25TAF/DWTV (H968) metal dome on sale for $17

http://madisound.com/sale.html

and a Peerless 5.75" mid 850234 for $13

http://madisound.com/new.html

[RoyC]

Thanks for the links, Pete. I'm still undecided what to do with the NHT's. Time and other limtations may keep them in the closet for awhile. I would probably be more inclined to use them as a sub with various small 2 way speakers at some point. They may even end up on Ebay as they've never been out of their shipping box!

Since it pertains to this thread...I received a few of the pots/rheostats loudsubz discovered. They are virtually a drop in replacement for the old AR3a pots for less than $2.00 each...a steal.

Roy

[RoyC]

I should add, however, that if someone is going to the trouble of removing the pots, and the originals are restorable or available refurbished, it would be wise to stay with them. The old ones are still easier to reinstall and won't diminish the resale value of your original speaker. Like it or not, AR3a's are becoming quite costly to purchase and have considerable value in the collector's market. If restored properly, they will last a long time and have substantial resale value to boot!

Roy

[mluong303]

Here is a properly restored job on the AR Pollak pots.

Picture shown Before and After of a pair Acoustic Research 15 Ohms pots in the classic AR speakers which had been disassembled, cleaned and lubricated to last for many years to come. Even at this level of workmanship, I can only state as minimized death spots.

[mluong303]

This is the original AR-1 Ohmite 25 Ohms pot. Yes, tweenty five Ohms. It was built like a tank and definitely over kill construction to drive the Altec 755A full range driver.

[dynaco_dan]

Hello

The decision not to carry the 8 ohm tweeter version based on purchasing 2,500 unsold units is a wise decision.

The sales may be poor and that is a lot of money to tie up.

However, with a little promotion, there may be sufficient interest to accumulate prepaid orders.

Carlos must have some indication as to how many interested parties have made inquiries over the last few years.

Even a survey on this website might work.

I have written on another thread about a AR 3/4" tweeter that I have which has a sand cast resistor glued to the rear of the magnet housing. I believe it had a sticker on the back about being a replacement unit.

It is still packed, so I can't confirm the resistor value but I believe it was an experimental version of the 8 ohm tweeter with a suitable parallel value (tweeter about 5.75 ohm +/- plus parallel perhaps 3 (un-educated guess) ohm resistor) to bring the value down to the equivalent 2.75 ohm +/- approximate 4 ohm tweeter.

If the one resistor lead is clipped you still have a 8 ohm (5.75 ohm +/-) equivalent tweeter.

It was not mounted for series wiring as I remember.

If this is true, then the 8 ohm tweeter would be the one to stock, not the 4 ohm.

With the added resistor of course.

Adding a 4 ohm +/- resistor in series is not in my mind a very good engineering decision. But what do I know?

Good luck.

Carlos at AB tech is telling the Truth. Even way back to

>1990, AB Tech had servicing blown AR 8 Ohms tweeters that way.

>It is a bit strange but this is the only go around way to fix

>the problem with genuin AR tweeters. The replacement AR-3a

>tweeter cost $62.50 at the time and not too many people will

>pay that price to fix their AR-2ax or AR-5 speakers. But for

>the people who own AR-3a, AR-LST or AR-9 etc., they will more

>likely to pay for the tweeters and get their AR speakers back

>to service again. That is why AB Tech have no intension to

>order the 8 Ohms version. Each batch of order has to be

>minimum of 2500 units or so.

>

>In 1992 at the time AR was still in MA. The US made 3/4" cloth

>dome with Ferro fluid cool tweeter were running out of stock

>and AR started to contract Tonegen in Japan to build the AR-3a

>drivers. It all started with 500 pairs of custom order AR-3a

>limited speakers which were ordered by Ming Fat Company of

>Hong Kong, the exclusive AR importer in the Far East. These

>AR-3a speakers were distributed mainly to Hong Kong and Taiwan

>and some ended up in Japan. Very few AR fans in the U.S.

>really acknowledge about this fact. I had a hard time trying

>to buy a pair from AR since AR had made an agreement to ship

>all 500 pairs to the over sea market only. Few unassembled

>brand new AR-3a limited cabinets and small amount of unused

>AR-3a Limited crossovers later on were sold in the US market

>when AR moved to Benicia around 1993. Alex of AB Tech and Ken

>Kantor are the two people who do know the existence of these

>AR-3a Limited speakers... The two pots were replaced with two

>15W 8 Ohms L-pads. I wish Ken still remember who was in

>charged at the time and is there any way to locate the

>crossover schematic for this AR-3a Limited speaker which had

>slight change in Cap and Coil values to go along with the 8

>Ohms L-pads. They still crossover at 575Hz and 5000 Hz. The

>cabinet was 3/4" MDF covered with walnut vinyl. During this

>time the Green Planet wave and Environmental protection issues

>are going on strong. The terminals opening was rounded corner

>rectangle instead of the round opening we are familiar with.

>

>I strongly recommand disassemble, clean and lubricate the 4

>pots rather than bypassing them. The truth of the matter is

>these 4 pots will allow you to fine tune the output levels of

>the tweeters and the midranges to a closer match. The fixed

>resistors will not give you this option. If you are not handy

>enough or just don't want to bother with the pots then you can

>certainly use four 8 Ohms 15W L-pads for replacement. They

>should be dropped in replacements with no need for any

>openning modification. Don't bother with the 16 Ohms or huge

>50W which will be a hassel do deal with.

>