ESS AMT-1 Tower Restoration

[GabeD]

Hi all,

My first post here! I have been lurking for many years though.

I inherited a pair of ESS AMT-1 Towers from my dad. Over the years he had an enormous speaker collection that was constantly in flux. Advent, Altec, JBL, Bozak, ESS, Bose, EPI, Ohm, AR, Sansui, Pioneer, Tannoy, Empire, Cerwin-Vega, Klipsch, EV, you name it, he probably had a pair at one point. He had a friend in the late 70's that worked at an audio shop that sold him many wonderful toys, some of which I have now.

I know that he had a set of the AMT-1 pyramids from 1978, purchased new from his friend, and as a kid in the 90's I remember he had more than one pair, I'm guessing different B,C,D versions as at least one set had poly woofers.

Anyway, I'm pretty sure he got the Tower version some time in the late 80's early 90's. He moved a couple to times and over the years they got a little banged up and neglected. Our cat growing up was not kind to the grille cloth either. The mounting holes for the woofers were trashed with the particle board crumbling from the original over zealous sealant. Since bringing them home I have been in the process of restoring them by rebuilding the crossovers, repairing and refinishing the cabinets, sorting out the Heil's with new diaphragms, and putting in new woofers.

He had so many parts over the years and I think he may have experimented with the Towers a bit. When I got a hold of them they had 8 ohm Advent woofers (he re foamed countless sets of woofers so I doubt he took the originals out just because of rotted foam, maybe he was playing with different drivers and how they sounded or had a bad voice coil), the Heil AMT's did not match in style or impedance and the brightness selection switches were not working at all. I ended up with 3 AMT's. One is the older box style, one is a box style with no side caps and one is the hourglass style. I have a feeling one of them was in a set of bookshelf's (he had a pair of those too) as it has the angle brackets for mounting. One had no diaphragm, the hourglass style has an 8 ohm diaphragm and the last one has a 4 ohm diaphragm.

What was very odd to me though was that the cabinets are slightly different. One set has a larger opening around the top surrounding the Heil and the other has the cutouts right up next to them. The location of the hole for the crossover is at different heights and the spacing inside the cabinet between the top of the transmission line and the hole for the woofer is about an inch different. The cabinets are about 700 apart in serial number. Does anyone have any information as to if ESS had an update or manufacturing change? I don't remember him having two pair of these at any point so I'm assuming he bought them on the used market like this.

Notice the spacing at the top where the tweeter mounts:



And the height difference of the binding posts:




A huge thanks to Porkloin and his many posts throughout the various ESS threads. This one was particularly helpful. The nut plates, though a bit of a pain to install, are such an elegant solution to mounting the woofers. The recommendations for parts for crossovers and the willingness to share ESS knowledge is greatly appreciated.

I have them re assembled and am very much enjoying how they sound. The Heil is just so open and airy and the transmission line style cabinet really sounds great in the bottom end. It's quite surprising what the pair of 10" woofers can do. I have a matching pair of new 4 ohm diaphragms that sound great and went with the heavy duty 4 ohm Goldwood poly woofers.

On my to-do list is to clean up the veneer and to restore the grilles with new cloth and badges. I like the idea of using magnets to hold them on. I'll see if I can get some "after" pictures uploaded.

If anyone has any info on the Towers and if there were different versions of them I'd be very curious to know. Thanks!

 

[GabeD]

Below are the photos of the crossovers in their original state. Some of the electrolytic capacitors were paralleled to create a specific value and they must have been tested at the factory as some had values written in black marker on the case. When I restored the crossovers I used the values in the schematics that are available from the current version of what is ESS here. Page 10 is what I was working off of.





















The brightness selector switches were corroded and the wipers were loose so it made sense to go ahead and just replace them. One of the PCB's was loose as the plastic stud on the mounting plate was broken off. The 40 year old capacitors needed replacement and the fuse holder and binding posts were looking corroded as well. Definitely time for a rebuild!

 

[GabeD]

The cutouts for the woofers were in very rough shape. There were chunks missing and some of the original sealing putty was still holding on in places. I scraped all of that away and removed the loose wood chips to prep for the Bondo. I used wood Bondo to build the lip the woofer sits on back up and once cured sanded everything flat. I tried a Dremel but even that was difficult to get into the groove so a lot of hand sanding was used to get the lip even.







For the cabinets I used wood filler on the small holes and then sanded things smooth. I did an initial coat of satin black from a rattle can to see how things looked. The spray method turned out to be streaky and the paint soaked into the wood so quickly it was very difficult to get an even finish. I ended up sanding things down lightly again and used a roller to put on Rust-oleum enamel in satin black from a regular can. It was much easier to apply and the coat was very even.

 

[Porkloin]

Sweet acquisition. I trust that you'll cater to your inner audiophile OCD and make the smaller tweeter cutouts bigger to match? Did the crossovers have the same value?

 

[GabeD]

I'd have to get a router if I were to attempt to get the tweeter cutouts to match. I'm not sure if it would be worth tempting fate with the old brittle particle board. I'd have to chug a lot more audiophile Kool-aid to make that happen.

That is what threw me - everything was the same except for the cabinets. The AMT's being different, I assume, was because of my dad tinkering, but the crossovers were a match. The lettering on the back plate is a match and the original components matched in value and style.

Is there any info on the different versions of the AMT's? Were the boxy ones earlier and the hourglass ones later? The diaphragm size was the same. The hourglass had an 8 ohm diaphragm and I'm pretty sure was not originally with the Towers as they are rated at 4 ohm and call for 4 ohm parts. They looked untouched under the warranty stickers. With all of the ESS stuff my dad had over the years I think I am dealing with AMT's from three different models.

 

[GabeD]

This is how the crossovers came out. Pretty much everything was replaced except the inductors and PCB. I used Mils resistors, Parts Express Dayton Audio polypropylene capacitors, NKK rotary switch for the brightness selection, Screw Cap fuse holder and correct fuses. New binding posts replaced the corroded old style originals and were a perfect fit.

















I put a line of speaker gasket on the back of the crossover where it meets the cabinet to seal things up. The screw cap fuse holders are much better than the T wing style. I had to enlarge the hole a tiny bit to get the new one to fit but you can't tell at all from the outside. The correct fuses were installed replacing the paper clips that were being used.

I also upgraded the wire to 16ga to feed the drivers and connect to the terminals. 20ga connects the caps on the daughter board. New bolts, washers and standoffs secure the boards to the back panel replacing the broken plastic posts.

 

[RxDx]

Welcome, and very nice work! Tested the sound yet?

 

[GabeD]

Oh, yes, they sound wonderful. So open and airy sounding. I grew up listening to JBL L-80's and 4410's with their titanium tweeters so I am used to "bright" sounding speakers. While I find the JBL's to be infinity listenable and still use them in my living room and office, the ESS just have an enormous sound to them. The tweeters in the JBL's have a very tight easily locate-able sound source but the ESS sound open yet coherent.

I understand why some people hear a "hole" in the midrange of the AMT-1 series of speakers but it is not something that has bothered me. I suppose it is what you may be used to and, as with all of this audio craziness, it is completely subjective. James Taylor sounds fantastic in both his vocals and guitar. In his more recent albums such as New Moonshine and Hourglass there are some extremely low bass notes that really let the T-Line cabinets shine. The Edie Brickell album Stranger Things has some very interesting raw electric guitar which is very accurately reproduced. And my absolute favorite band Steely Dan, well, it sounds exactly like it is supposed to, layered, rich and complex.

I'm driving these with a Carver M-400t I recapped and fixed up so there is plenty of power at 4 ohms. I have dreams of finding a second one and run them as monoblocks.

 

[GabeD]

I read a lot about woofer replacements in the ESS. A lot of the recommendations were to go with the originals. I wanted to get these up and running without waiting for something to pop up on the 'bay so I went with the Goldwood GW-10PC-4. The highly recommended Eminence 10" driver is no longer available new. I read that it was a bass cabinet driver and that the thinking was that because it is an instrument driver it could produce more midrange than a hi-fi driver. The new ESS drivers that are out there are the "squircle" used in the pyramids and did not apply to the Towers as they are standard 10" circles. I may have been able to shoehorn them in but wanted things to look nice. I do like the little ESS logo printed on them though.



I choose the Goldwood because it was a good mix of availability, price, build quality and sensitivity at 92.7db to try to keep up with the Heil AMT's. It is also rated up to 2,500hz and my hope was that being poly would help with the midrange response.



They are well built as well with cast frames and a larger magnet structure than the originals.





They are held in with hex head screws and nut plates inside the cabinet. It was extra effort to install the nut plates but was completely worth it. It is so easy to pop out the woofer if necessary and I don't have any fears of damaging the particle board cabinet.

 

[automojo]

Hifi- not pro woofer....

 

[GabeD]

Indeed. That is the driver I came across in researching. I think the issue I had was trying to find a 4 ohm version of it. Also, the page you show appears to be sold out. Just their stock perhaps?

 

[homebrew]

Nice rebuild of the ESS, up to the woofers. Can't endorse using just any woofer with the right impedance that fits in the hole. Correct replacements (assuming they're available) mean they would be tuned for the cabinet to get the best response. Those are nice speakers, deserving original woofers. Nice refurb of the crossovers though. Good thing you kept the original inductors.

 

[GabeD]

I ordered two diaphragm replacement kits and installed them into the two box style AMT's I have. I have the hourglass version set aside for future use. I pulled the 8 ohm diaphragm from one of the box style and will keep that saved as well.





Oops, I voided the warranty!



The AMT's were mounted on the foam pads that came with the speakers. I found some terminal blocks at Frys and used them in place of the original cracked plastic blocks.



I'm not sure if it was original to the Tower model, but one of the AMT's I have came with an aluminum bracket which went across the top. It was in bad shape so I made up two new ones from 1" flat aluminum bar stock from Home Depot. To these I affixed the warranty stickers that came with the replacement diaphragms. The diaphragms themselves seem to be an exact match for the original that was in the hourglass style AMT I have. The leads both come out of the same side. My only gripe is that there is a misspelling on the warranty sticker provided in the kit - the "disphragm" being removed will void the warranty. Oh well.

 

[automojo]

A poly cone is more self damping then a paper cone.. they lack the sensitivity of paper.. the small details are smoothed over. There is a time delay in their response that is fairly noticeable with the Heil.
The crossover will prevent the woofer from having any response at 2500... i’m sure it’s not the smoothest up there anyhow.
The new ESS paper cone, or this Misco legacy driver would be a much closer to O.E. the a poly cone.
Personally not a big fan of the ESS Bextrine woofers either... they seem to squeeze the life out of the music and gloss things over like poly. Clean, but fairly lifeless.
In the tower, the original woofer works well.
The Heil is about smooth articulate detail.. paper is the only way to go IMHO
Nice rebuild by the way!!

 

[jcidave]

GabeD: Welcome to AK. You did beautiful work on this restoration. Very nice work on the crossovers. You should hang out your shingle. The very earliest Heils were boxes with no end caps. This looked unfinished, so the end caps were developed. They started to cut out the plastic in the housing to improve vertical dispersion. It ended up looking like a figure 8. Unfortunately, this reduced the strength of the plastic holding the halves together so they fracture and come apart easily. The metal strip is used to provide support to help keep the halves together. Wasn't necessary or provided in the original box design.
ESS was always making production run changes to its products. They also used different fabricators. You might have two cabinets from 2 fabricators. With the grills on, the finished speakers would look the same.
The grill frames for the 1 Towers, AMT3s and AMT4's were nailed on with brass brads. Really not designed to come off.
If you really want OEM woofers, there is a guy who sells OEM used ESS parts on Ebay who I have mentioned in previous posts. But with all you have done, I don't know why you would feel compelled to do that.
Enjoy your speakers!

 

[automojo]

Sure-wasn't trying to discount your restoration effort-one of the better I have come across for sure. My point was there is a huge difference in the detail of a paper cone, particularly in ESS/Heil speakers, vs a poly-carbon fiber etc. It's easy to hear. I think you would be surprised...I was for sure..
(I played with a number of woofers, including the Goldwoods-actually too many to count. But I was looking for a totally seamless sound-where it wasn't the Heil, transition driver, or woofer show. One where the speakers just disappear, and you have music, and little to no compromises from bottom to top, and also achieved my goal of extending bass response, with audible output to 25hz (AMT3).
Lot's of work, too much in hindsight-but the results are exactly what I was looking for.
Funny-your dad and I sound like we might have had a few things in common-looking for that perfect speaker...)
Some of the paper vs poly is a matter of taste as well.
The Misco, and 1040SF improve on the O.E. design-along with the new ESS woofers. Stronger magnets, better materials, etc. The issue I have with the original woofers-is not only are they 40 years old-40 year old cones-but particularly the Alnico's-they loose magnetic flux.
As a whole-they were acceptable woofers at best for the design/times.
For the price that seller on Ebay commands for his O.E. (I bought a pair of O.E. AMT3's mids from him a couple years ago)-you better off with a more modern woofer-as long as it's specs are compatible with you enclosure volume, venting-sealed-etc, and crossover points.
Every ESS speaker I have had in the past, with Bextrine, or poly-never came close to the the paper cones models. Sure they had good bass, but lacked a huge amount of 'speed' and detail.
Again, not knocking your choice, just some food for thought.....
As mentioned, Impressive rebuild-much like Will's. I settled with acceptable looks-and I figured most people facing the same challenge would find things easier that way, and geared my threads as such-Will took the cabs to more than several levels above look wise-but I left him in the dust sound-wise!! . The whole part of my early AMT3 threads.
I kind of dig some of the battle scars (minor on both sets) they have-it tells their story…..
It would be interesting to work with the transmission line/different woofers-I settled in the end on a totaled sealed woofer setup, as every configuration of ported/quasi reflex loaded enclosure seemed to lag behind the Heil.
For myself it took at least a month or to of listening to grasp what I was hearing, what was going one-before I made changes.
I will have to look back-but I tied at least 10 different woofer configurations before settling on the 1040's.
As mentioned, the Misco has a similar heritage, so to speak....

 

[GabeD]

automojo, thank you for your input! Finding the woofer that fits best seemed to be the rub with this model, and it seems other ESS as well. I am open to experimenting with different options as budget and time allow. I think it would be interesting to compare the poly and paper woofers and their different sound characteristics. Thinking about it now, I remember my dad not liking the way the Bextrine version of the AMT-1 pyramids he had sounded.

jcidave, thanks for the historical perspective. I guess things have changed in the way products are manufactured - we are used to seeing millions of an item be made exactly the same way churned out endlessly now. The bracket I ended up with must have come from the hourglass version that I have. I put the box version without the side caps on the cabinet with the smaller cutouts and the one with the side caps on the cabinet with the larger cutouts. I like the way they look and my misspelled warranty stickers are already attached to them so I will leave them in place.

Do you have any clues as to which version is correct for the Towers? More so out of curiosity than anything.

The restoration of the Towers has been a labor of love for sure, not just because they were my dads, but because they are an interesting piece of audio history. And they sound so good!

Veneer and grilles are next on my agenda. I really like the looks of the towers without the grilles so I will likely forego the brass tacks and attempt a set of magnets to hold things together so I can easily remove them.

 

[automojo]

Sure. It seems the Misco woofers is really a bargain IMHO. It's a throw back for sure-but it seems speaker manufactures, in the name of trying to eliminate what they thought where draw backs, distortions, colorations-squeezed the life blood out of speakers. maybe they sounded 'clean', but lifeless.
Once you get the woofers/bass/damping really dialed in-they difference will astound you, over previous incarnations. When the Great Heil, can operate seamlessly-with it's supporting cast-its a joyous, and mind-blowing experience. Probably what your dad was looking for-as the potential is there. Easy to hear.
I think the Goldwood HD is a great woofer-just not on par with the Great Heil. It's all about touch and texture and timing, on level with the Heil. A heavy damped cone just doesn't cut it.
I would imagine the towers, with their internal structure, are fairly solid.
The AMT3's were not-I added bracing between the 2 woofer opening, and upper woofer and mid tube opening. This made a huge difference. I also treated the interiors with a ceramic sealer/sound damper-lines the walls with 1 1/2" foam-and ultimately in their sealed condition-3 lbs of fiberglass per enclosure. They tip the scales now at 140 lbs ea.
I agree the 3's are a good looking speaker too naked. You should post some pictures of your finished product.

 

[jcidave]

GabeD: The AMT1 Tower came with the box type Heil with no cutouts. By the time I was involved selling them, they had added the side caps to the box. That extra diaphragm in your pic is also an original from the 70's. Its one step up from the very first generation. When the diaphragm is overdriven, the conductors heat up and the pleats will eventually stick together and then melt together. This was happening with the early diaphragms, so they put 3 rows of silicone across the pleats to help control this problem. Then they abandoned the silicone fix and put bridal veil lace across the pleat surface to try to do the same thing without the restriction of the silicone. You will also notice that the old one has 17 or 18 pleats. The new ones have 12 or 13 pleats.
I have a wide variation of different diaphragm generations in my group of ESS speakers including several pair using diaphragms with Kapton substrate (yellow in color) which ESS used for a time in the 90's.
All my old diaphragms sound and perform well. There is no compelling reason to change them.

 

[automojo]

I agree on the old diaphragms. Their can be a slight db output difference between old and new-so sometimes if you fry one, you need to replace both.
Back in the 80's I had a pair of 3-way PS1220's I purchased new-Alltronics South Bend Ind-Great speakers, and got me hooked on the Heil.
They got lots of use-usually at high volumes, so I went through a number of diaphragms-a few woofers and passive slabs. ESS had a great exchange program on the woofers, and slabs.
When I bought these, I went digital at the same time-so they where a real eye/ear opener.
Why they don't have the Great Heil (nothing like it for sure) they are the only other ESS Heil speaker besides the AMT3's that doesn't have the slight hole in the crossover region. Some of this depends on your music type/program material, and you ear sensitivity in this region.
I know a lot of the dealers didn't like the stamped frame woofers of the AMT3's, vs the Monitors.
IMHO the stock 3's sound was decent enough, but they should have sealed (and braced) the cabs (some ironically where made this way) and gone with woofers that could dig deep.
The 1040SF's easily go to 25hz with out issue. Not that most music has any content below 40 hz or so, but the effortless sound quality you get with woofers that are basically on cruise control in that region makes a huge difference.
The stock 3 woofers always seemed (and sounded) like they were trying to play catch up.