Yet another AR-4x refurb

[JKent]

A fellow New Jerseyan bought some reproduction speaker badges from me for his AR-4x's. Those speakers are special to me because they were my first (in 1969). They were also my first refurb project, with plenty of help from CSP members (John O'Hanlon in particular). I asked to see photos and noticed one non-AR tweet so I asked if he'd like me to work on them.

These were in relatively good condition but had one Rat Shack tweeter. The owner bought a pair of what he thought were 4x tweets from an ebay seller in Canada but they turned out to be 4xa tweets (with front wires). Our options were;

1. buy another 4x tweet
2. use the 4xa tweets with an adapter plate and xo mods
3. buy the phenolic ring tweets on Parts Express

The owner chose the 3rd option so I sold his one good 4x tweeter (will also be selling the xa tweets) and ordered parts from PE.

There were a couple of cabinet dings, a chunk out of the hole where the RS tweeter had been mounted, the pots were very corroded and the protective cloth on one woofer magnet had a hole in it.

One pot had been bypassed with a paper clip!

More to follow.....

[JKent]

Here are some shots of the work and after photos. I hope the owner brings the grilles so I can get a picture with the speakers "fully clothed"

• The dings were filled with a mixture of epoxy and fine sawdust.
• The open seam was filled with the same mix, then clamped to close it.
• The missing chunk was repaired with J. B. Weld's "Quick Wood" (epoxy stick).
• The front baffle was painted with some leftover semi-gloss Rustoleum.
• Cabinets were LIGHTLY sanded then wiped down with Howard Restor-a-Finish (Mahogany) followed by 3 coats of Watco Danish Oil (Dark Walnut).
• Pots were replaced with L-pads from PE plus 25 ohm resistors.
• Knobs were installed on the L-pads. They're cheap Chinese knock-offs but they look just like the original DakaWare knobs used on this era speakers.
• A hole in the cloth cover on a woofer magnet was patched with some sheer black cloth and Alene's Tacky Glue.
• Original wax capacitor was disconnected but left in place. New 10uF surplus caps from Madisound were wired in parallel to make the 20uF (more on this to follow).
• Cabinets were re-stuffed with the original fiberglass (about 20 oz. per).
• Phenolic Ring tweeters were installed. The screw holes line up but I used a Dremel to make room for the terminals. I used PE's foam gasket tape on all drivers. The original machine screws were missing from one speaker so I used three #10-24 machine screws, painted the heads black. The 4th screw is a coarse thread wood screw from PE, driven into the epoxy patch.
• Woofer surrounds were treated with Roy's cloth surround sealant.
• Roy's sealant was also applied to the tweeters. This is a trick he discovered as a means of "taming" the PR tweets (if you look at the Vintage AR versions you'll see they've been treated with Roy's goo).

Next....listening tests.
-Kent

[JKent]

Listening test:

When I first fired these up I thought my ears would bleed . Then I realized the L-pads were turned all the way up. Turning them below the 1/2-way point improved the sound immensely.

I'd had MANY discussions with Roy about this project (Thank you, Roy!) and he suggested I try changing the xo cap values to 10uF. Makes sense--the 4-xa had a 10uF cap.

I experimented by pulling a tweeter and wiring a 20uF cap in series (thus lowering the capacitance to 10uF) and it sounded pretty good. Roy had commented that it is safer to use the 10uF (vs the 20) because it will reduce the amount of power to the tweeter at lower frequencies, thus offering more protection.

So I went back into the cabinets and snipped the leads on one of the 10uF caps. A waste of $1.20 but I wasn't going to pull them out and re-do the crossovers!

So here they are. Even on spackle bucket stands and less-than-optimally placed, they sound good!

-Kent

[owlsplace]

Looks good.

I probably would have opted for the 4xa tweeters though, but that's just me.

Roger

[JKent]

I probably would have opted for the 4xa tweeters though, but that's just me.

Well, maybe I would too except the xa tweets were front-wired. So besides making an adapter plate I would have had to fashion some sort of baffle-mounted terminals (probably brass machine screws) and fiddled with those fragile tinsel leads. I was doing this as a favor (i.e. freebie) and didn't want to mess with those.

Many people have reported success with the PR tweeters and to me the speakers sound good. And now they have brand-new tweeters (in addition to new caps and L-pads) so I think they'll last a long time. But I hear what you're saying.

-Kent

[DavidDru]

Good stuff Dr. J! Look perty now.

[stupidhead]

I like the red 2. They sure look better than before, your friend got a nice set of speakers in the end.

Personally I would have sourced a 4x tweet or two and kept it OEM.

[ra.ra]

Very nice job as always, Kent - - looks like you've probably assembled a very good speaker for this owner with a minimum of financial investment. Like yourself, I try to achieve at least a slight red tint when I refinish walnut veneer, and that dash of mahogany really gives those cabinets a wonderful warm glow.

A couple things you have mentioned caught my attention, and I admit I'm a bit baffled about this phenolic ring tweeter, even though I have one right in front of me on my desk as I write. Not having seen a cross-section drawing of this driver, I'm just not quite sure how the phenolic ring is intended to function, particularly with that sliced section removed to allow passage of the wire leads. On mine at least, it appears that the paper cone is attached to the rear of the inner ring, while the outer portion of the ring is attached to the metal basket frame.

You are correct that the PR tweeters from Vintage AR include this application of sealant at the juncture between the cone and phenolic ring, but why does this tweeter require user-applied "taming" in the first place? Is it, by nature, simply a "squawker" under certain circumstances? I saw your comment about initial ear bleeding, but then the L-pad was able to dial that back to provide a far more acceptable balance, so clearly you have already provided a wide range of HF control with the L-pad/resistor combo.

Not doubting that the experimental cap change (20 to 10uF) produced some noticeable improvement, but there are two things I do not understand. First, why does this brand new, robust, contemporary tweeter require more protection at lower frequencies? Vintage-AR explicitly states that "no modifications are required" when using this tweeter as a drop-in replacement. Also, while I agree that the 4xa indeed did use a 10uF cap for its particular tweeter, I didn't understand your comment about why that cap value would thereby make sense for use with the PR tweeter. Each of the AR "4-series" models used a different tweeter design and accommodating cap value (AR-4 with 6uF; AR-4x with 20uF; AR-4xa with 10uF), but up until this thread, I had always thought that the PR tweeter was an affordable, reasonably acceptable, and very simple drop-in replacement requiring no further modifications.

I like this project , and you always do great work with ample research, but I remain curious about the need for this additional tweeter damping and the rationale behind the change of cap value. Did you ever A-B the 20uF cap version against the 10uF version?

[RoyC]

Very nice job as always, Kent - - looks like you've probably assembled a very good speaker for this owner with a minimum of financial investment. Like yourself, I try to achieve at least a slight red tint when I refinish walnut veneer, and that dash of mahogany really gives those cabinets a wonderful warm glow.

A couple things you have mentioned caught my attention, and I admit I'm a bit baffled about this phenolic ring tweeter, even though I have one right in front of me on my desk as I write. Not having seen a cross-section drawing of this driver, I'm just not quite sure how the phenolic ring is intended to function, particularly with that sliced section removed to allow passage of the wire leads. On mine at least, it appears that the paper cone is attached to the rear of the inner ring, while the outer portion of the ring is attached to the metal basket frame.

You are correct that the PR tweeters from Vintage AR include this application of sealant at the juncture between the cone and phenolic ring, but why does this tweeter require user-applied "taming" in the first place? Is it, by nature, simply a "squawker" under certain circumstances? I saw your comment about initial ear bleeding, but then the L-pad was able to dial that back to provide a far more acceptable balance, so clearly you have already provided a wide range of HF control with the L-pad/resistor combo.

Not doubting that the experimental cap change (20 to 10uF) produced some noticeable improvement, but there are two things I do not understand. First, why does this brand new, robust, contemporary tweeter require more protection at lower frequencies? Vintage-AR explicitly states that "no modifications are required" when using this tweeter as a drop-in replacement. Also, while I agree that the 4xa indeed did use a 10uF cap for its particular tweeter, I didn't understand your comment about why that cap value would thereby make sense for use with the PR tweeter. Each of the AR "4-series" models used a different tweeter design and accommodating cap value (AR-4 with 6uF; AR-4x with 20uF; AR-4xa with 10uF), but up until this thread, I had always thought that the PR tweeter was an affordable, reasonably acceptable, and very simple drop-in replacement requiring no further modifications.

I like this project , and you always do great work with ample research, but I remain curious about the need for this additional tweeter damping and the rationale behind the change of cap value. Did you ever A-B the 20uF cap version against the 10uF version?

Phenolic ring tweeters are a style of cone tweeter. It was/is an inexpensive type of tweeter used in many systems over the years. As with dome tweeters, they vary in electrical and mechanical characteristics from model to model. To use your terminology, ra.ra, the PE tweeter is a bit of a "squawker" with peaks in the upper midrange. The 20uf cap used in the 4x is unusually large for a tweeter in this type of system, which only enhances the PE tweeter's issues. (Carl has posted measurements relative to this tweeter's issues elsewhere, and I agree with him). If it is sounding acceptable to Kent, the 10uf cap simply makes more sense when not using the original tweeter. There is no reason to believe the PE tweeter is as, or more, robust than the original AR tweeter.

To be clear, "Vintage AR's" business is not directed at purists. For example, he sells 8 ohm l-pads without 25 ohm resistors as replacement controls, Boston FF 10 inch surrounds upon request only, lesser grill cloth than the preferred oem-like "Lambswool", and feels the PE tweeter works "well enough" as is (I suggested the cone treatment to him). If he doesn't receive complaints he stays the course (complaints are very rare and never about the stuff we discuss here). His philosophy is to keep it simple and to make enough of a profit to make it worth his while. He is not an "audiophile" in any sense of the word.

Roy

[JKent]

Thanks all for your comments. A couple of things: First, remember these are not my speakers. The owner was not inclined to search for another 4x tweeter, especially not after having purchased the 4xa tweets.

Some of the questions will have to be handled by more technically savvy types. I don't know how the phenolic ring works. As for taming, it's not that the PR is a squawker but it's louder than the original Also, the 4x crosses over at 1200Hz--quite low, so the tweeter is taking over more mid-frequency tasks than usual. The PR tweeter has a frequency response of 2,000 to 15,000 Hz. My reading of that is the PR tweeter will be hard pressed to fill that 1,200 to 1,500Hz range. I think lowering the cap value effectively raises the crossover level.

Carl wrote a thread about taming the PR tweeter that involves putting a 0.1mH inductor parallel with the tweeter. To tell the truth I simply relied on Roy's expertise to employ a simpler solution (i. e. applying his goo to the tweeter). And yes, I did A/B the 10 vs 20uF. To tell the truth I don't think I heard a consistent difference (but my ears are old) . What I did not do (and this would have been an important comparison) is compare the PR to the original tweeter. I just didn't have a 100% original 4x available for comparison.

Maybe my comment about bleeding ears gave the wrong impression. With the tweeter level cranked ALL THE WAY UP they sound harsh. The PR tweets have a sensitivity of 90.3dB and I believe the original tweets are significantly lower. With the level set somewhere below 1/2 the tweeters sound right and the overall sound is very pleasing. I've listened, briefly, to a variety of music: well-recorded jazz (Jazz at the Pawnshop on Proprius), classical (Beethoven's 6th Symphony on Telarc) and some rock (Graceland, Dark Side of the Moon on MFSL). All good.

-Kent

PS: Looks like Roy slipped a reply in while I was typing. He's the "more technically savvy type." Apparently the PR tweeters ARE squawkers when pushed down into the upper mid range.

[xmas111]

Kent, nice job on those. You have a masterful touch with cabinetry work. They look beautiful and your friend should be thrilled with them!

I'm still amazed at how good the 4x's sound for their size.

John

[ra.ra]

Thanks, guys - - helpful responses to my questions. Will get back with small follow-up when I get a chance. Am on-the-run today.

In total agreement with John.

[owlsplace]

Kent, seeing all the variables here, I'd say you did a bang up job on these; especially if there is any chance the user will over-drive these speakers since there are readily available drop-in replacements.

Just wondering if there would have been an advantage taming these tweeters with a pot vs the L-pad or if that is just a moot point?

Roger

[JKent]

Just wondering if there would have been an advantage taming these tweeters with a pot vs the L-pad or if that is just a moot point?

Roger,

I honestly don't know. Maybe Roy will comment. I remember we had some discussion about Carl's mod, which used a 0.1mH inductor. Roy had asked whether Carl used an L-pad or pot (he used the original pot).

-Kent

[stupidhead]

Thanks all for your comments. A couple of things: First, remember these are not my speakers. The owner was not inclined to search for another 4x tweeter, especially not after having purchased the 4xa tweets.

Just to be clear, wasn't suggesting you (or your friend) made the "wrong" choice. Only saying what I probably would have done. As always, in the end if you like the sound then it is all good.

I am curious as to the red 2 lug, was that his/your idea, or was that existing. Keeping the wiring the same on each set is very important as we all know.

Geoff

[JKent]

Geoff,

No problem. I understand. Most of us here like to keep our classic speakers as original as possible. I'll be returning them to the owner tomorrow and I'm sure he'll like the sound. btw--nothing here is irreversible. If anyone wanted to install original 4x tweeters they'll screw right in and the only thing to do would be to install a short jumper where I snipped the lead of one 10uF cap in each box. Easy-peasy.

The red 2 is some red nail polish from the $1 store. I put it on there in case the owner has any question about which wire goes where.

Looking at your interests, you may be interested to know my compensation for this job was a 6-pack of IPA Not craft, sadly.

-Kent

[RoyC]

.Just wondering if there would have been an advantage taming these tweeters with a pot vs the L-pad or if that is just a moot point?

Roger

Using the 25 ohm parallel resistor (as seen in Kent's photos above) is virtually the same as using an original pot. That is the point of using the resistor with an L-pad. So no...no advantage at all.

Roy

[owlsplace]

Using the 25 ohm parallel resistor (as seen in Kent's photos above) is virtually the same as using an original pot. That is the point of using the resistor with an L-pad. So no...no advantage at all.

Roy

Yes, electrically, but would there be finer control over the tweeter output level?

Roger

[RoyC]

Yes, electrically, but would there be finer control over the tweeter output level?

Roger

No...and even if it did it would not do anything about the offensive peaks at certain frequencies.

Roy

[owlsplace]

No...and even if it did it would not do anything about the offensive peaks at certain frequencies.

Roy

Okay, I am looking forward to a decent equalizer sometime next year