ESS AMT-1 Tower Restoration

[automojo]

A couple AMT3 crossover variations. The second one is a specifically fine tuned, low inductance, no compromise hardwire version. Over the years I managed to pick up serval extra pairs of AMT3 crossovers to experiment with.
It would be interesting to compare the sealed bass response vs transmission line on how it matched up with the Great Heil.
The back of the hard wire crossover has a multi layer gasket that, along with the thick crossover board, does a amazing job of deadening the fairly lively rear cabinet panel of the 3's.
I also gained 1.5 db in increased output do to the higher efficiency
EDIT:the Heil and mid caps in this crossover have been replaced with a mix of Mundorf Evo Oils and Janzen Superior Z's So a total of 4 caps to replace the stock 31uf mid and Heil caps.
If your considering this-with stock crossover board-the Janzen's are quite large-so you would need to construct a outboard mounting plate to accommodate them.

 

[automojo]

And just thinking on the woofer, and their characteristic sound. It may sound strange, but I think whatever a drivers materials are-well that's what they kind of sound like. Plastic, metal, paper, etc. Same for a speaker cabinet materials, plywood, MDF, plastic, metal, fiberglass, etc. And maybe that's was in part the reasoning on the Bextrine/poly cones ESS used. They thought it would be a better match for the 'plastic' Mylar/Kapton diaphragms.

 

[jcidave]

automojo: That certainly could also be part of the logic for the switch to the Bextrine/poly cones. I also think the prevailing discussions in the 70's centered around the woofer not being fast enough to keep up with the Heil. So the thought was a thinner, lighter plastic cone would be faster. This certainly ties into your thought process. However, the paper cones are much more rigid and a better piston in my opinion. The poly cones have a lot of wall flex. So the current ESS replacement woofer product has a coated paper cone.
I only have 2 speakers in the collection with poly cones. A pair of 1B bookshelves custom ordered from ESS over 20 years ago and this pair of Monitor cabinets I added this year with a second active poly woofer since I had an extra pair of poly woofers laying around.

 

[automojo]

Nice!
Yep I remember those-and the added vents.
What I have leaned over the years messing with my 2 pairs of 3's among other speakers, is it seems the 'fastest' (term used loosely) and most detailed bass seems to be a old school paper cone with poly ether/foam surrounds. Like the poly cones-it seems the traditional rubber surrounds don't provide as clean or fast piston movement. Obviously you have to take foam surround maintenance into account.
Rubber is good at damping the cone movement, but in turn you loose detail.
Seems all of the speakers I have head over the years-the ones that had really remarkable bass has paper/foam woofers, or even paper cones/fabric surrounds. And where usually sealed as well.
A common speaker-the Large Advent-is one of them-once you could get around the sub par tweeter.

 

[jcidave]

GabeD: So after going a bit off on a tangent with your thread (Sorry), I do hope you post some final pictures of the completed project. I think you have documented it very nicely. When the ESS guys start talking about our speakers, its a little hard for us to increase the damping factor.

 

[scoloheros]

There's thread or posts somewhere having to do with placing a wedge in front of the tweeter that blends the tweeter with the woofer a little better but I can't find that anywhere. I do notice a little gap in midrange with mine and I want to try the wedge. They electronically demonstrated the gap in mid-range with and without the wedge.

 

[jcidave]

Yes. It starts off with "Give Oskar a Wedgie" If you search on that you'll find it.

 

[BigElCat]

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:

View attachment 1547740

And the height difference of the binding posts:

View attachment 1547741


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!

Sweet !

If they were mine, I'd enlarge those tweeter cut outs so they matched. But not with a router.

I'd use a hole saw at each corner so the radii (radius's) were the same, maybe 3/4". Then a fine tooth blade in a jig saw.

 

[GabeD]

GabeD: So after going a bit off on a tangent with your thread (Sorry), I do hope you post some final pictures of the completed project. I think you have documented it very nicely. When the ESS guys start talking about our speakers, its a little hard for us to increase the damping factor.

Ha, no worries at all! The main reason I started this thread was to learn more about what I have and try and decipher the mishmash of parts this pair of Towers became over the years, so thanks to everyone for their thoughts!

Regarding the diaphragms, it is interesting to see they made changes over the years. I wonder if they were all Dr. Heil approved!

I ended up with three AMT's:

- Box style no side caps - had no diaphragm in it when I found it in my dad's attic
- Box style with side caps - had an 8 ohm diaphragm in it - the one pictured earlier with the silicone lines
- Hourglass style - has an 4 ohm diaphragm in it (looks to be untouched original) has the lace

The first time I got everything back together and gave them a listen one channel was much brighter than the other. I initially thought I had made an error with one of the crossovers but after a bit of troubleshooting I realized that the diaphragms did not match in impedance.

I ended up getting two replacement diaphragms and put them in the box style AMT's to try and match things aesthetically. The hourglass style appears to have a larger gap between the magnet "fingers" sticking out.

What model speakers would have had a box style AMT at 8 ohms?

 

[GabeD]

Nice! Rubber is good at damping the cone movement, but in turn you loose detail.

I have a pair of JBL 4410 Monitors that were re surrounded at one point. They are the correct drivers but have rubber surrounds. I really want to remove them and put the proper JBL surrounds on. The foam is so much more thin and light compared to the rubber. I did a pair of L-80t3's at one point and was sure to get the proper JBL surround instead of a standard 10" surround. The profile and thickness was pretty different.

 

[scoloheros]

Yes. It starts off with "Give Oskar a Wedgie" If you search on that you'll find it.

Finally!, thanks, I've got to save that. I typed all I could think of in the search box, don't know why I couldn't find it, operator error somehow of course. I never blame the computer like so many do. I used to train people at workstations, it was always the computer's fault and not the operator's haha.

 

[jcidave]

Yes. A Wedgie. Attached is my feeble attempt to make a Wedgie diffuser. I only made one pair of these and put them in one of my 2 pairs of AMT 1A cabinets. I did not do any critical listening to these and don't have any measurement gear.
GabeD: If you look closely at these, you will see a cutout only at the top of the Heil box. Another Heil variation I believe first seen in the AMT 1A cabinets. This kept the bottom of the box intact for structural strength. The back of the top also has the cutout.
I have also made rear diffusers out of scrap wood just for something to do. Here is a pic of that on the other pair of 1A's. I believe there are other threads that discuss other forms of diffusers for the Heil.

 

[scoloheros]

What about one of these? I had one when I was a kid. https://www.amazon.com/Triangular-Refactor-Teaching-Spectrum-Photography/dp/B07GNX2W9F I can only find 4 and 6", never found a 5".

 

[jcidave]

Scoloheros: Yeah, that's an idea. Any of those sizes would do something. Doesn't represent a big dollar outlay either.

 

[toddalin]

Very cool!

I found that the wedge works best when it is just within the black base of the Heil. But with those extended bases, I guess you are in about the same place.

The clear wedge in the advertisement is 140 mm = 5.5". Depending on the "parting lines" on the Heil for the two halves, this may or may not fit within the cavity, but probably not. My wedges are 5.4" tall to fit within the cavity and its base it tall enough to get the triangle in there. I cut these on a chop saw with a coarse blade, but a fine blade would be better. The bases were cut on a laser cutter. My third attemp (bottom pic) uses stacked black acrylic pieces of a tear drop shape, also cut with the laser.

If the rod in the ad is lucite (as opposed to glass), it can be trimmed with a sanding disk/belt.

My second attempt used these. (First attempt used brass sheet.) For $10 you get 1 foot and can do both, assuming you can cut it.

This was the source.

https://www.ebay.com/itm/1-Pc-1-x-1...647619?hash=item44205b8fc3:g:WJAAAOSwT-lZmM4f

 

[jcidave]

toddalin: Your deflectors are very nicely made. I think you also did the measurements on them. There was an extensive thread about them earlier this year. A neat project to experiment with.

 

[BigElCat]

Y'all need the whole Transar set up.

https://audiokarma.org/forums/index.php?threads/ess-transar-rebuild-thread.723653/

 

[automojo]

Very cool!

I found that the wedge works best when it is just within the black base of the Heil. But with those extended bases, I guess you are in about the same place.

The clear wedge in the advertisement is 140 mm = 5.5". Depending on the "parting lines" on the Heil for the two halves, this may or may not fit within the cavity, but probably not. My wedges are 5.4" tall to fit within the cavity and its base it tall enough to get the triangle in there. I cut these on a chop saw with a coarse blade, but a fine blade would be better. The bases were cut on a laser cutter. My third attemp (bottom pic) uses stacked black acrylic pieces of a tear drop shape, also cut with the laser.

If the rod in the ad is lucite (as opposed to glass), it can be trimmed with a sanding disk/belt.

My second attempt used these. (First attempt used brass sheet.) For $10 you get 1 foot and can do both, assuming you can cut it.

This was the source.

https://www.ebay.com/itm/1-Pc-1-x-1...647619?hash=item44205b8fc3:g:WJAAAOSwT-lZmM4f

Finally got around to trying this.
Eh...I will pass.
My modded AMT3's-when I finally tuned in the internal damping (4lbs of R-19 fiberglass per speaker-2 added braces-foam lined walls into focus-its pretty amazing!
Especially sealed, but even ported, the AMT3 cabs are fairly resonate-even with bracing. Moving to a new place and wood floors confirmed this. Ess obviously was stuffing them brim full to counter act this.
So adding the deflectors ruined this.
And that's always been the point with the vintage ESS-particularly the AMT3's....the balance of the O.E. woofers-as the stock mid is fine.
Add this to tuning to your room.
Once you have the balance...it good from good to amazing..

 

[GabeD]

I finally got a chance to circle back around to these. It's grill time!

The original grills were falling apart. Our childhood cat had gotten to them in the past. Looking at pictures of other Towers online it seems that the grills that I have were missing the center section that went around the drivers. I don't know if there were variations on these or if they had been removed in the past.



I had removed one of the sides at this point.



The fiber panels were pretty beat up. There were remnants of old nails, staples and decaying glue.



After assessing what was there I decided to use the old grilles as a template and build new grills from scratch. I'll keep the originals tucked away somewhere.

I went to Home Depot and got a couple of sheets of hardboard:

https://www.homedepot.com/p/Hardboa...0-115-in-x-47-7-in-x-95-7-in-832777/202189720

This stuff was a little thicker than the original and is very hard. I roughed out the side and front panels and traced the areas for the holes using the originals as templates. A little (not quite so straight, but this will be hidden) work with a jigsaw and I had my panels ready to assemble. The thicker hardboard will hold staples better as well.



The front panel was not quite thick enough to clear the woofer so I used felt pads to push it out. I used some thinner pads for the sides. To hold the three panels together I used gorilla tape. It's not in the picture but I continued the tape on the entire seam.





Once I had them stuck together straight I laid them down and taped the back side.

For cloth I used Parts Express Mellow Tone black. I wanted to update the look of these and go with something a little more neutral than the red/brown stripes that were there. I like the look of the original cloth but my hope is that the current cat will ignore them and that it will increase the WAF.

https://www.parts-express.com/mellotone-premium-black-speaker-grill-cloth-yard-64-wide--260-332

I contacted them and asked if you ordered more than a yard would it be continuous. They said yes. Since that was the case with 3 yards in length and 64 inches in height I had enough to wrap the two towers.


A little trim and some stretching and a LOT of staples and things are coming together! I didn't want to mess with glue and the staples made it easy to stretch and attach to keep things from wrinkling.



Hopefully this evening I will be able to continue work on them. I can't wait to see how they look! Of course, I have one this far. I get to do it all over again for the second.

 

[jcidave]

All looks good. Just a couple of thoughts. The Gorilla tape is a handy product to use. My experience with it is that it will eventually loose its stick on certain surfaces. You might want to put a few staples through the front on the next grill. Will be interesting to see the effect you get with the stretched cloth. its covering a large area of light colored board and you might get some light color bleed through. You could spray bomb the front of the panels before you mount the cloth on the next frame. I think it will look darker.