New ESS AMT Monitor in the house, Newest generation (5th variation?)

[SaturationPt]

I was fortunate enough to find a second set of AMT Monitors, the same but different from the others.

The first set has the black heil, Bextrene woofers and passives with cloth double-roll surrounds, vents in both sides adjacent the Heil (with cloth matching the main grille), and a flat-mounted Heil.

The second set (high-7,000s S/Ns) also has the black heil, Bextrene woofers and passives, but with rubber surrounds, no vents in the upper cabinet sides adjacent the tweeter (solid sides), and the Heil is mounted on a wedge cambering it up slightly. This was original owner and has never been altered. (he also BTW showed me his AMT-1Cs stacked in the closet in their original boxes, got them new also).

So the question is, I am familiar with the first version with the cloth surrounds and vented sides, but what about the later one? Is this particularly rare/unusual? I did see a posting about a special / custom made pair without vents here somewhere, is this version 5?

Thanks for any comments up to and including berating me for being lucky enough to find a second pair without moving to the left coast to do so.

Yes the woofer's outer dust cap fell off, I'll put it back on.

 

[toddalin]

I don't know if this will help at all, but maybe you could get some info from the owner in the C/L ad I came upon the other day.
https://losangeles.craigslist.org/sgv/ele/d/ess-amt-monitor-speakers/6701597587.html

 

[SaturationPt]

Thanks.
I talked with the original owner a bit more, these were new in '82 or '83, and from S/N and other cues these are later than the changes documented here on AK.

Off to call ESS tomorrow and order parts.

 

[SaturationPt]

I can't say enough good about Rick at ESS, very passionate and helpful.

These are a later generation, not mentioned in the many threads here on AK.

Since the original owner bought these after loving the sound from his new AMT-1Cs, Rick feels that they must have been built in the early '90s.

Four versions are mentioned here on AK: early versions having the silver Heil / later black, early versions having the flat foam passive / later bextrene cones, early having foam surrounds, later with cloth.

This version has several changes not documented here:

* No side openings in the cabinet adjacent the Heil
* Heil mounted on a hard rubber wedge, angled up ~7 degrees or so
* Rubber surrounds on Bextrene cones, both woofers and passives
* Silver badges, not gold
* Tweeter protection capacitor added to the crossover network
* Simplified pedestal structure under the main cabinet, now black veneer on pedestal

I think that's pretty much it.

The angled mount on the tweeter is just to give the stage a bit more height, the Heil is only spec'ed at 30degrees vertical.

The tweeter protection, ... well probably a good idea.

The rubber surrounds were just a corporate change, these were manufactured after the AMT-1C and all changes rolled to all products.

The side openings around the Heil were apparently more of a styling than functional feature, and as such the style changed. Interesting that the new 12s have that opening again, ... I wonder if the new Monitors will also?

Rick's production estimate for the AMT Monitor series is around one million speakers through the entire run, compared to the AMT 1x series that was around 4.5 million.

 

[SaturationPt]

Restoration of both sets of AMT Monitors has begun.

First step was to source new surrounds for the bextrene cones. Although Rick states that the new paper cone woofers and new voice-coil design is better, it is also an additional $1,200. I want to try replacing the surrounds first (what do I have to lose?).

Pair 2 has rubber surrounds, just like the current / new drivers from ESS. I wanted to replace with rubber, but no (official) rubber surrounds exist. ESS buys the cones with surrounds attached, so doesn't even stock/handle the rubber surrounds. Simply Speakers lists a foam surround in their Factory ESS Parts however. Midwest Speaker lists some rubber surrounds that should fit, ... but the change to the speaker response is unknown.

The rolled cloth surrounds on Pair 1 are even more difficult to find.

Pair 1's cloth is super hard, both active and passive, so we have chosen to replace. Pair 2 rubber is cracking.

The decision was made to go foam on both. The transient response / speed has been what ESS is chasing to keep up with the Heils, and without extensive testing it would seem that a thin foam will be more compliant than un-known generic rubber or cloth surrounds, and I don't have the time for multiple changes and testing. Beside that, I have been told that the bextrene cones are very fragile and we will likely break most of them during this process.

The fabric surrounds actually came off of the bextrene surprisingly cleanly. I watched as my son removed, pulling and picking carefully by hand and with a razor-knife blade, wetting with isopropyl alcohol. The cone flats are pristine on all four of his cones.

I tackled the rubber surrounds. They were much more stuck, so as I pulled and picked I had little success. The final answer was to trim the rubber with a razor-knife at the edge of the cones. I haven't decided yet whether I will further risk the fragile and irreplaceable cones to try and remove a .5mm x 3mm strip of rubber to reduce mass as much as possible. I will probably try my luck a bit with the alcohol, but mechanical removal by pulling or razor-cutting will be risky. I might just glue over them.

New foam is inbound, as are diaphragms for the heils. We will also probably update Pair 1's crossover to the design in Pair 2. Pair 1 has perfect grille cloth, Pair 2 is getting new cloth.

I'll add pictures when we get the new parts and start reassembling later in the week.

 

[LostInTn]

Any update? New pictures?