The perennial 3a tweeter question - AB Tech?

[Guest winters860]

I've read and re-read the threads concerning replacements for the AR-3a tweeter. I think the following conclusions have been reached:

1) The AB Tech replacement tweeter ($125/pr) is the best replacement currently on the market.

2) The AB Tech replacement tweeter needs some crossover modification to blend well with the AR-3a.

3) There are CSP members, including Ken Kantor, working on perfecting said modifications.

I'm thinking of buying a pair of AB Tech tweeters. Would anyone mind popping out of the woodwork and give me their thoughts on the replacements' proper implementation?

[soundminded]

As soon as you begin re-engineering the system it is no longer an AR3a. Personally, I think you'd come closer to the original performance by cannibalizing a pair of AR2ax or AR5 tweeters and re-engineering the crossover network for any differences in sensitivity and of course impedence. I think those are the same tweeters as AR3a used except they have 8 ohm voice coils instead of 4 ohms.

[johnieo]

Greetings:

Again, it has taken some time to pursue this project, as the folks doing the work have jobs and families. Patience please!

The main issue with the original AR-3a tweeter is its slowly deteriorating urethane damping foam. The degree of degredation seems to vary; perhaps it dependends on conditions of storage and or use? At some point the used ones will not perform well and a replacement will be needed.

Ken Kantor and James have done extensive measurements on the new AB Tech tweeter as well as some good samples of the original tweeter. They are completing a report as we write. The preliminary value of x-o change is given in the thread "It's tuf to love a box;" however Roy C has done much careful listening and may suggest a small change in inductor value. He has put in as many hours listening as Ken and James have in measurement and analysis!

Selection of a replacement for this tweeter is being done on the basis of careful analytical measurements, the use of design software, and finally-- comparative listening. Personally, I feel that this is a much more substantive route than simply hypothesizing a replacement.

[RoyC]

Soundminded, I tried the 2ax/5 tweeter awhile ago...

The AR-2ax/5 tweeter simply does not have enough output. As it is, the more sensitive old 3a tweeter is having trouble keeping up with the other drivers these days. Most folks have the tweeter level control maxed. On the other hand I have installed 3a tweeters in 2ax's and 5's (with a slightly larger cap) and found it provided a very pleasant boost.

John and I agree. Many of the old 3/4" domes of the 3a/2ax/5 construction have deteriorating foam suspensions which is affecting output and response, especially at lower frequencies. The excursion is not what it was 35-40 years ago (kinda like many of the bodies in this forum...myself included :-)!). Anyway, the foam under the dome is also deteriorating causing possible response issues as well. I have dissected a number of these tweeters with the same unfortunate findings. The pics are posted somewhere in the forum.

Some folks find the old tweeter capacitor sounds "better" because the old deteriorated caps actually may be allowing a lower crossover point for the "handicapped" tweeter. The new cap raises the crossover point to the original point, and sometimes results in tweeter response that is grainy or harsh, and, at the same time, LESS detailed. This would be due to its inability to extend satisfactorily into the midrange. It is sometimes reported as sounding "different" or worse than the original, and among other things, debates over cap types and brands ensue unnecessarily.

Ken has provided some very helpful measurements and graphs, and I have been experimenting with the AB tech tweeter based on his info, and sharing it with co-conspirators. As I type this post, I'm listening to a pair of "AB Teched 3a's" and I am convinced they can be made to sound as good or better than any 3a *in current use*. The details are still being worked out, but a parallel inductor of .05mh to .07mh with the tweeter, and some well placed resistors should do it.

The AB Tech tweeter is not the most refined tweeter available and it is pricey, and if the AR-11 era tweeter was still available we would be having an easier go of it, but it IS sounding quite good to me at the moment...in a very "3a way"!

Roy

[Pete B]

Just wondering Roy, have you tried an AR-11 tweeter in an AR-3a?

As a drop in without mods?

Also, obviously you could copy the AR-11 tweeter crossover,

have you compared to see which provides a closer AR-3a sound?

How does the level match? Do you have to run the 11 tweeter

full up also?

I'm asking because I have an AR-11 tweeter here, and it could

serve as a reference if I knew how it works best in a 3a.

[Guest winters860]

Don't feel like I'm pushing anybody. Thanks for pointing me toward the relevant (and relevatory) thread. I hadn't updated myself on its' later developments. I guess I'd be best off picking up a pair of those AB Tech tweeters and sitting on them.

Am I on the right track when I say that the current version of "the mod" in that thread consists of adding a .07 mH choke in series and a 15 ohm resistor parallel with the AB Tech tweeter (and maybe some sort of a blanket on the tweeter to tone it down even further)?

[RoyC]

Hi Pete,

No I have not used an AR-11 tweeter. I sent a similar, but higher impedance AR-12 tweeter to Ken, and those measurements are included in his data. The AR-11 tweeter was later used as a replacement tweeter for the 3a and LST, and in general I have heard good things about it. It would seem it would also need a parallel inductor like the #14, .105mh used in the similar AR-11. I've been told that was the tweeter the AR-3a Limited tweeter was based on, with its 4uf cap and .16mh inductor.

Roy

[johnieo]

>Am I on the right track when I say that the current version of

>"the mod" in that thread consists of adding a .07 mH

>choke in series and a 15 ohm resistor parallel with the AB

>Tech tweeter (and maybe some sort of a blanket on the tweeter

>to tone it down even further)?

Not quite! If you read that thread carefully, it states that the 15 Ohm resistor is ONLY for the AR-LST.

Roy has been listening to the AR-3a with some slightly smaller values of L. I think he has abandoned the felt. Give him a couple of days to conclude what he has discovered.

Cheers,

[RoyC]

This is as good a place as any to begin discussing the 3a.

My initial reaction to the .07mh coil was that there seemed to be an un-3a-like edge in the higher frequencies, so I experimented with felt diffraction rings...which resulted in trying a larger AR-11, #14, .105mh coil. The felt did take the edge off, but I believe it was sucking too much life out of the tweeter, and likely hurting dispersion.

I've bagged the felt, having moved on to smaller than .07mh coils. The results are very promising, as I mentioned above. Such things as l-pads vs pots, and adding series resistance to new caps, are also being taken into consideration.

That is really all I'm willing to share in a public forum at the moment. I don't want anyone messing up their speakers on my account. However, if anybody has 3a's with AB Tech tweeters, and are willing to dig into them, email me and I'll get you started. I can promise you that we are WAY past the sound of "dropped-in" AB Tech tweeters, and are now rapidly reaching a point where more ears will be needed. On the other hand, if you love the sound of dropped-in AB Tech tweeters please leave them be, as this outcome will sound quite different.

Roy

[Mexicomike]

Interesting re the AB tech tweeter. Although new to this site, I been an audiophile since I was 16 and had AR products throughout the 60's and part of the 70's. As the current new owner of a set of 3a's, I belong to the school of "Leave 'em alone - if you modify them they aren't AR 3as any more." HOWEVER...

In my self-rightous dogmaticism, I overlooked the fact that when I had my original 3as, I had a set of Microstatic tweeters on top of them to "improve" high freq dispersion. They were specifically made/marketed to match the ARs (and other similar speakers, I guess) with the same walnut veneer case and similar grill cloth. Whether it really "improved" the sound, I'm not so sure now but according to Microstatic, they did!

The point is, that I was "modifying" my AR3as back then to get "better" sound. So my initial feeling that they shouldn't be modified at all is a bit hypocritical from a sound perspective though not, I'm sure, from a "collector" viewpoint. Then again, the microstatics could be viewed (and, by George, I think I'll view them this way) that they were not a MOD of the AR, just an add-on unit that sat on top. Wonder if the same approach could be applied now?

As a final point, what the heck am I doing? Am I having a major mental meltdown? Why am I recreating the stereo system I had in the late 60's - AR 3a, AR TT, AR Amp? Bizarre!!

[roundhome]

call me stupid many have but why if we are going through all this to mod are speakers .WHY are we using a expensive one sorce only tweeter insted of a off the shelve less expensive one.

why ??????????????