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Old 24th June 2014, 10:26 PM   #1
diyAudio Member
Join Date: Jun 2003
Location: Hamilton, was Ottawa (Canada)
Default ESS AMT Monitors (Heil Air-Motion-Transformers), refurb

Hey all,

I inherited a pair of ESS AMT Monitors with "the great" Heil Air Motion Transformers! Wow, I'm just blown away by the quality and workmanship. Oh and they're a bit flimsy ... Nearly busted my hump carrying them to my car and 2 story walk-up appt. by myself!

AMT Mon w grill.jpg

ESS AMT logo.jpg

AMT Mon dusty.jpg
Oh you poor thing, all dusty ... and that's dust that came through the grill cloth! Nasty, ... and smells like Old Man.

Having trouble finding specs, manual, xover schematic, etc ...

Here's good ol' HiFi Engine - Owners and Service Manuals

ESS Monitor Manual - Loudspeaker System - HiFi Engine

Powerful in it's sonic delivery, tall and stately in appearance, the AMT Monitor represents the utmost perfection in ESS's superlative AMT series.
The AMT monitor effortlessly unleashes thundering crescendos with great force, yet deftly reveals the most subtly detailed musical tapestries.

Type: 2 way, 3 driver loudspeaker system
Frequency Response: 30Hz to 23kHz
Power Handling: 375W
Crossover Frequency: 1000Hz
Impedance: 5Ω
Bass Radiator: 305mm cone passive
Bass: 305mm bextrene cone
Tweeter: heil air motion transformer
Grille: black, brown
Finish: walnut veneer
Dimensions: 997 x 397 x 403mm
Weight: 47kg

Wait ... 997mm x 397mm x 403mm is ... 39"x15"x16" and 47 kg is ... 104 lbs. No wonder I almost busted my hump!!!

It was sooooo worth it!

So here's the Great Heil (all cleaned up)

the Great Heil.jpg

ESS AMT Monitor.jpg

ESS AMT Monitor PR.jpg

The 12" passive radiator just ... dissolved! All that's left is the Styrofoam disk!

So, it seems like there were a few versions of the Monitor:

from "L7" at ESS AMT Monitors - Page 4 - Home Audio Stereo Discussion Forums

I guess it goes without saying that when the crossover says AMT MONITOR that one would surmise they are AMT MONITORS.
Not trying to be the fly in the ointment but hey...
Four unpublished revisions took place on those AMT MONITORS. None of these four were labeled anything other than, AMT MONITOR.
Early versions were with silver AMT units, metalized capacitor films, bextrene woofer cones w/ open cell foam surrounds, and .75in styrene disc radiators on the aluminum rings w/ the same suspension.
1st mid-build revisions came with flat black AMT units, bextrene woofer cones w/ rolled-edge treated surrounds, and .5in styrene discs w/ open cell foam suspension.
2nd mid-build revisions incorporate a huge change to the radiator, they were made to reflect the same outer rolled-edge suspension of the bextrene woofer and updated to a conical bextrene passive. When this radiator was introduced, it attached to an entire cast woofer frame (less the magnet and motor structure) obviously. The inner coil area behind the dual dustcaps was sealed up with an inverted pulp disc.
Final build revision on the AMT MONITOR came circa 1979 when they utilized the SBR (styrene butadiene rubber) half-roll suspension on both the bextrene woofer and conical bextrene radiator. This final build was in production during the outphasing of the 1B towers hence the SBR suspension changeover, which the 1C line of towers took on exclusively.
Hope that helps some confusion on the whole "MONITOR" thing ESS did lol... not to be confused with the entirely different builds of the AMT3 and the AMT1AM which were housed in the identical footprint of 15.75x15.75x39.5 inches respectively



Mine is the 1st version with the simple passive radiator: just foam surround and 0.75" Styrofoam circle (or is it the 2nd because it has the flat black Air Motion Transformer--AMT?) I'll need the replacement kit, it's:

PART# ESSPR-12 $28.95 usd (12")
ESS Laboratories USA (Replacement Passive Radiators at bottom)

Also available at

Official Speaker Repair Site - Orange County Speaker - Home of GLS Audio

Simply Speakers - Official Speaker Repair Page - Speaker Parts and Repair Service

Not sure if these are "official" ESS ones but they're the best price:

Official Speaker Repair Site - Orange County Speaker - Home of GLS Audio 12" or 10" Passive Radiators (choose size)

Then maybe later I'll upgrade to the more advanced passive radiator: speaker without voice-coil (cone passive).

ESS Factory Replacement Passive Radiator, 689-12P

I've been listening to them (even with no passive radiator: no deep bass and a bit 'boomy') non-stop for 3 days!

Yesterday, I was walking by and ... the next thing I know 2 hrs had gone by! Like some sort of time warp!

Here's pics of the xover and the back panel:

ESS AMT Monitor back pannel.jpg

xover and passive radiator.jpg


Anyone know where to get official stats, manual, xover schematic?

I've emailed Ricky "Rico" Caudillo at Ess (ESS Laboratories USA) and will post his reply.

Oh and it looks like Nelson used to work on the 10" woofer version at (Electro-Static Sound) ESS in Sacramento way back when he was just getting going in audio!

Thanks and cheers,

Last edited by AudioLapDance; 24th June 2014 at 11:28 PM.
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Old 25th June 2014, 02:10 AM   #2
puppet is offline puppet  United States
diyAudio Member
Join Date: Dec 2011
Location: The Dells, WI
Looks like the same frame as their "rock monitor" ... that's the one NP worked on. Dual 10's w/6" mid.

The configuration you have could use the amt 1b xo. same/same 12" w/12"PR and a 1k xo point. Don't have a schematic for it though.
Attached Images
File Type: jpg ESS_amt_1b+10b+1b_bookshelf+Monitor_(7).jpg (312.5 KB, 140 views)
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Old 28th June 2014, 10:11 PM   #3
diyAudio Member
Join Date: Jun 2003
Location: Hamilton, was Ottawa (Canada)
Default All hail The Great Heil!

Thanks puppet,

You're right, they look similar: Monitor and AMT 1b and ...

Lots of AMT 1b stuff over at audiokarma:
ESS AMT-1b Crossover - Home Audio Stereo Discussion Forums

Repost here SVP!

All Hail the Great AMT Heil!

All Hail the Great Heil.jpg

Last edited by AudioLapDance; 28th June 2014 at 10:30 PM.
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