Rehab of ESS AMT 1 speakers

[klamsoss]

Hey all you AKers out there. Hope you are being safe, staying home if you can, and being smart when yo do have to go out.

I'm starting my next audio restoration/rehab project. This time it's a pair of ESS AMT1 speakers that I am hoping to bring back to their original sound as a wedding gift for one of my best friends. He picked them up a few years ago with the intention of having them rebuilt, and I figured I would just do it for him. I've looked over a bunch of rehab threads for ESS speakers, and there's a lot of good info but none that cover my specific questions.
What I know so far:
1. Serial numbers are A1398 (I think it's a 9, but the tail isn't imprinted) and B8721. Pics 1 and 2. So I'm thinking they are from different production runs, and likely different years.
2. They have totally different woofers(see pic 3) . No idea when or if either was replaced. Both are completely missing foam and one has a slightly pushed in dust cap.
3. The AMT units look like they may not match, either, as one has a slightly taller gap between the main cabinet and the body of the AMT unit itself.
4. They appear to have the same value components in the crossovers but one is obviously newer.
5. The wiring for the tweeters has been messed with on both of them, and one is missing the side caps on both sides of the AMT unit(see pic 4). The wiring pattern doesn't match, one has a fuse wired in, and the other looks like it was just bodged together.
6. One of the AMT diaphragms has been messed with. The sticker was removed, and there was no sign of any putty. It also looks like the pleats are stuck together on the right side(pic 5). I tried to gently separate the pleats but they're stuck good.
7. I'm rebuilding the grills, which were in rough shape, but I think I understand what I'm doing there. I don't plan to refinish the cabinets. They are in decent enough shape as-is.

Sooooooo...
The easy:
4. Replace the caps in the crossovers with quality polypropylene films from Dayton Audio. I don't plan to do anything else with the x-over, but if there is a quick, cheap, easy, and widely recommended change/upgrade, I'd be willing to give it a try.
6. Replace the diaphragm that seems to have sticky pleats on the side.

The less easy stuff:
2. Not sure if I should try re-foaming the mismatched woofers, or just get replacements from ESS/Simply Speakers. These are clearly different magnet structures, though, so I'm thinking just re-foaming might lead to different sounding speakers.
3. Don't know if the missing side caps on the AMT unit makes a difference. If so, I'm not sure if replacement side caps are readily available.
5. I have no idea what the wiring for the AMT units is suppose to look like, if adding a fuse is actually a good idea, or if it's best to take them off for the rehab.

What do you guys all think? I'm trying not to get too deep in terms of money, but I'll spend what I need to. Thanks in advance, all!

 

[VanArn]

The early coated polyethylene pleated diaphragms in the AMT were capable of working with a crossover frequency around 800 Hz. Unfortunately they do not hold their shape forever especially when subjected to high power and there is a danger that the flat wire conductors can short together in spots. Replacement with new diaphragms, Part No.689-1107 is advised and remember to ask for resistance matched pairs when ordering. The crossover frequency will need to be raised to 1200Hz, which involves designing a new xover which will need an impedance correction network for the bass speaker and a correction network to flatten the rising response of the AMT at the higher frequencies. It might be better to convert the cabinets to use 8'' speakers ( 4 ohm ) with a sensitivities of around 92 dB SPL for one watt input.

 

[Guest159]

Those woofers should work and sound about the same. The one is an alnico magnet and the other is a ferrite magnet version designed to drop into the same applications as the alnico drivers. ESS doesn't sell replacements for those 10's. I wouldn't replace them or modify them for a different or smaller driver. ESS used those exact same drivers in speakers that crossed over as high as 1500Hz and I owned a pair that did just that so I know they do it just fine.

As for the crossover, I'd go through that thing and reflow all the solder joints with flux and a little fresh solder. I had a bitch of a time with brittle joints breaking after I had the crossovers in mine out to recap them. After the third time a joint broke I ripped them out and reflowed every joint and never had another problem. I used Solen PP caps in mine. Film caps are going to brighten those AMTs up a little so putting some slightly higher value resistors in the ladder might help.

Appearance-wise, filling, sanding, sealing, and shooting those top halves in matte gloss black made them exactly match the color and texture of the housings of the AMTs, and that looked really nice.

 

[swechsler]

Does any sound come out of the sides of the AMT tweeter when you play them? If so, you'd probably be best served by replacing those missing pieces. To my knowledge, the only parts sold for those are the diaphragms. If you have access to a 3D printer, maybe you could print a set of the missing sides.

Regarding the woofers, @ReactiveLoad has already given more info about them than I could. I'll just warn you that the (double) dust caps on my AMT-1C woofers fell off due to poor adhesive. Now, these were some sort of composite cone and dust cap, and yours are paper, so it may not apply to you, but you should double check yours to make sure there is absolutely no separation between the dust caps and the cones. If so, they should be glued back - a thin bead of glue like Aleene's around the circumference should do the job. Even the smallest gap between dust cap and cone can cause buzzing when they're turned up loud.

 

[klamsoss]

@VanArn, appreciate the input, and you clearly know what you're talking about, but I'm not trying to redesign the whole speaker. I'm sure it would result in a superior end product, but I just don't have the time to teach myself everything necessary to design and test all of that. Maybe someday, but not today.
Generally speaking, I know for dome tweeters (especially ferrofluid cooled) it is advised to always replace them in pairs because of the potential difference in sound. Is it advised to always replace AMT diaphragms in pairs as well?

@ReactiveLoad I see that 10" drivers are for sale for these from simply speakers, but if these are similar enough, I am one who generally prefers to stick with original parts if I can. Sounds like a refoam kit is in my future.
*update* just tested the impedance of each... they aren't close. 4.1 ohm on the round magnet, and 3.4 ohm on the square. Not sure if that changes anything.
I definitely plan to resolder all joints in the crossover, and could adjust the resistors a bit, but I'm no expert in crossover design and with only a 10ohm and a pair of 2ohm resistors, I'm not sure what "slightly higher" would mean. I suppose I could just go with 10% tolerance resistors and hand pick the ones that are on the high end of that 10%?
I plan to bypass the poly caps with russian PIO 0.1uF caps, as well, but I don't have experience with how that impacts sound in speakers (or doesn't). I only know I really prefer the PIO for signal path in my tube equipment.

@swechsler , I haven't run signal to these yet because the woofers were foam-less from the start. But that's a good tip on the 3d printer. They have one at the public library here in Cincinnati so if I hear sound out of the sides once I have these back together, I'll definitely look into that(whenever it opens again). As for the dust caps on the cones, they are glued on tight. I tried to see if I could gently peel either of them back at all, but no dice. They're on there good so hopefully no buzzing. BUT, if I fire them up and hear bees, I'll know where to start.

 

[GabeD]

Generally speaking, I know for dome tweeters (especially ferrofluid cooled) it is advised to always replace them in pairs because of the potential difference in sound. Is it advised to always replace AMT diaphragms in pairs as well?

I restored a basket case set of AMT1 Towers recently.

https://audiokarma.org/forums/index.php?threads/ess-amt-1-tower-restoration.874994/

The diaphragms in the AMT's I had did not match in style or impedance. I discovered the impedance miss match after rebuilding the crossovers. I thought I had made an error with them but it turned out that one diaphragm was 8 ohms and the other was 4 ohms. I ordered replacements for both to get them as close as possible as the 4 ohm version I had looked different from what was on the Simply Speakers site. The ones at Simply Speakers were 4 ohm, which was correct for the Towers, and after dropping them in they sound perfectly matched. I'm very very happy with how they sound after being restored.

 

[Guest159]

I don't know how obsessive you want to be with those, but alnico drivers are the correct drivers for those and they do have a sound of their own. They pop up on eBay every now and then. I didn't want to stray from the original formula. I bought mine from a guy who'd taken great care of them and they didn't need much work. I personally feel like those drivers are rare and unique and I wouldn't replace mine unless they were totally destroyed.

If you really want to go hog wild with the crossovers, replace those resistors with good wire wound non-inductive parts. Not sure I'd bypass the caps. PP caps already perform really well.

 

[jcidave]

A couple of thoughts. The very earliest version of the box great Heil did not have end caps. So either this one is an extremely early version or the end caps came off. That was known to happen. I would contact ESS to see if they can sell you a pair before you try to reinvent this wheel. I have a [pair like this. It does not affect the sound.

The diaphragm you show is also a very early version. 16 or 17 pleats, no silicone across the pleats, no bridal veil and the leads are separated on either side of the frame. New diaphragms have 12 pleats. These old ones are somewhat more fragile than newer diaphragms. Simply speakers or ESS itself for these parts. These are drop in parts and don't need crossover mods.

There is no reason to change the crossover frequency unless you want to change the fundamental sound of the speaker. Other than recapping if you wish to, I would leave the crossover point alone.

These woofers look like they could both be OEM woofers, but from different eras. Early series woofers would have had ALNICO magnets. Unfortunately, ESS bought from different suppliers and made mid production run changes. If you want to try to match them, I would contact ebay seller 83fj to see if he can help you.
There are threads here on AK about people getting aftermarket woofers for AMT3s and AMT1 Towers. Any of these woofer selections will work in your 1s.
For something to do, I bought a pair of ESS cast frame replacement woofers and just surface mounted them on my second pair of 1s. Its working for me.
Good luck with your project.

 

[klamsoss]

Since the woofers that came out of these are measuring significantly different impedance, aren't from the same era, and use different magnet structures, I think I'm going to replace them. It seems like the best way to ensure they'll sound the same when finished.

So I'm now trying to decide what woofer to use. Looks like there are some very good options available for fair prices. I'm concerned about power handling on some of the popular replacements (Misco) but like the idea of sticking with a paper cone.
These are going to be driven by a Marantz 2325 which puts out a hefty 125wpc (I'm also restoring that for my buddy). So power handling is a consideration. The Misco is rated at only 50w.
Was looking at:
https://www.parts-express.com/visaton-w250s-4-10-woofer-with-treated-paper-cone-4-ohm--292-574
Or
https://www.parts-express.com/peerl...8cp00-04-10-paper-cone-woofer-4-ohm--264-1598
Both seem to be in the right neighborhood in terms of parameters, though they both recommend dual ports. Not as high of power handling as I would prefer, but still better than the Misco. And a bit less coin than the factory 10" drivers from ESS, which would necessitate some reconstruction of the cabinet for secure mounting.
Any thoughts?
What's the power rating on the tweeters, anyway?

Also, while I identified that the crossovers were basically the same, they are actually both modified, and in different ways. I can't really make sense of what the previous owner was trying to do, so, those will need to either go back to stock, or be tailored for whatever woofers I end up with.

I really hadn't intended to redesign the whole speaker, but it seems like that's where I've landed.

 

[jcidave]

Looking at this again, trying to keep it less costly and more simple, I'm first in the camp of re-foaming the woofers you have and trying them. That's also been suggested in a previous post. They may sound more similar than you think. Even if they look different, the company would have tried to maintain the same basic sound. Then you have no cabinet mods.
I don't have the exact power handling of the Heils and I can't say that I've seen it printed anywhere. I have a pair of Heil Elites which is just a Heil and a crossover used as an add on tweeter. This is fused with a 3ag one amp fast blow fuse. At one point in time I think ESS had a separate in line fuse for the Heil in one of the Monitor or AMT3 cabinets. I believe this also was a 1 amp fast blow. So, if you feel compelled to protect the Heil, You can certainly add an infuse behind the Heil with a 1 amp fast blow. But as original from the factory, the Heils were not separately fused in this system. The entire system is fused with a 2amp fast blow fuse. I would say though for your friends benefit, new diaphragms are in order. I have not damaged the Heils in my 2 pair of them, nor have I blown the fuses. But I run tone controls flat. Who knows what your friend is going to do.
I'm not much help on crossovers. There are others here on AK that are. You can down load the Xover schematic for free on the ESS website. There is also a Service Manual you can down load on that site as well. It tells you how to replace diaphragms on the various Heils. The Service Manual has an intro page about amplifier power that is an interesting read. Its one of the reasons why I have always believed you can never have too much power.
Unfortunately, a matched pair of 1 Xovers that had been recapped just sold on Ebay not unreasonable cash.

 

[puppet]

I'm in the refoam camp as well.
Forget about the DCR mis-match. You've got two different style's of woofer and who knows what the voice coil spec's are for each.
Fix the surrounds and if there is a big difference in sound quality between either then look to replace the woofer style that works best for you (copying the XO if different). Speaking of the XO's, don't know how you can tell if they have been altered from factory. AFAIK, factory XO's were all over the place component wise.

 

[jcidave]

I am also tracking a thread called ESS AMT-3 replacement woofer candidates. That OP just completed his project using the Dayton RS 270P 10 inch woofers.
If you refoam your existing woofers and want to take this further, you may want to consider these.

 

[klamsoss]

@jcidave good tip, but those are 8 ohm woofers. I'm pretty sure I need 4ohm, or to do some crazy action, like completely redesigning the whole shebang and turning these into towers with 15" subs in separately ported enclosures attached to the existing cabinets, which would then employ a 10" full range eminence driver like those found in my Tektons, crossed over around 3kHz, for the woofer in the AMT1s, and developing my own home-brew crossover for the lot of it.

But really, I should probably lay off the stiff manhattans, not spend more than I did on my own system, and stick to the plan. Refurbishing a 2325 with top notch parts and rebuilding a pair of ESS AMT1s is already a pretty good wedding present. Beats the hell out of a blender or some BS cookwear.

I'm actually going to get on a call tomorrow with ESS, see what they say, then call Dayton Audio, see if they have input, and make some contingency plans. Ultimately, step 1 is to refoam the existing woofers and give them a listen. If they sound bad, then the worst case scenario is I replace both woofers with matching units and then I have these two left over with which I can pass on to help out others who are in search of a match for their single drivers. Pay it forward, ya know?

 

[GabeD]

So I'm now trying to decide what woofer to use. Looks like there are some very good options available for fair prices. I'm concerned about power handling on some of the popular replacements (Misco) but like the idea of sticking with a paper cone.

I'd be curious to see what a suitable 10" 4 ohm driver for ESS would be as well. The AMT1 Towers I have had Advent woofers in them when I got them. Currently I have Goldwood GW-10PC-4 woofers in them though I would be curious to roll some different woofers, likely paper cone as the Goldwoods are poly, to see how the sound changes.

The Eminence 1040sf woofer that is highly recommended is no longer made and looked to only be available in 8 ohms. I was looking at the Misco woofer mentioned earlier but have the same reticence about the power handling at 50 watts. The Goldwoods are rated at 150 watts and the Towers at 400 watts at 4 ohms however I have no idea what the original woofer by itself was rated.

The Dayton RS 270P is rated at 90.9db and the Goldwoods are rated at 92.7db. I'd imagine the woofer needs to be as sensitive as possible to try and keep up with the AMT. They look pretty cool though with the bullet in the center.

Like the AMT1, the AMT1 Tower uses a circular frame, not the "squircle" that are available new from ESS now.

 

[jcidave]

Sifting through the Parts Express catalog, I did see some 4 ohm versions of the RS 270 woofer. One with a hybrid paper cone and one with an aluminum cone. Both of these are more pricy, so this takes your project in the wrong price direction.

Back in the 70s, I saw a small classified ad in the back of one of the stereo magazines for this product. I was tempted, but never bought a pair. For someone who is somewhat crafty, I don't think it would be too difficult to duplicate. But this is for another time and another day.

 

[klamsoss]

WOW!!! I honestly had no idea that this existed!
Looks like it's just a very basic, non-ported resonant chamber that the normally-ported AMT1 sits atop?
That would be incredibly easy to construct from materials we have left over from the wet bar we put in the basement.

 

[jcidave]

WOW!!! I honestly had no idea that this existed!
Looks like it's just a very basic, non-ported resonant chamber that the normally-ported AMT1 sits atop?
That would be incredibly easy to construct from materials we have left over from the wet bar we put in the basement.

I agree. That's what I think it is. I would doubt that the improvement, if any, is any more than subtle. If anything, it will get the Heil and woofer higher off the floor and give you a different perspective. I tried to look this business up once, but I think its long since defunct.

 

[automojo]

This one should work perfect in the AMT1.
Similar specs to stock. Paper cone, poly ether surround 1 1/2 voice coil.
Power rating is conservative-should drop right in!
Plus USA made-a bargain IMHO!
Looks the part of O.E> as well.
https://store.miscospeakers.com/10-inch-woofer-93053
With a EBP of 77, you could experiment plugging the port.
FIY those use 4ohm woofers.
Using 8 ohm will double your crossover point.
IMHO too much is made on the Great Heil crossover point on the AMT1
IMHO the AMT1 was the best of that pyramid series.
Tight bass, that works with everything except bass heavy techno/etc.
Use a sub at that point-even though I'm not a sub fan.
The AMT1 is a music maker-not a sub shaker.
The Eminence 1040SF would have been ideal-it needs to be run sealed.

 

[automojo]

Since the woofers that came out of these are measuring significantly different impedance, aren't from the same era, and use different magnet structures, I think I'm going to replace them. It seems like the best way to ensure they'll sound the same when finished.

So I'm now trying to decide what woofer to use. Looks like there are some very good options available for fair prices. I'm concerned about power handling on some of the popular replacements (Misco) but like the idea of sticking with a paper cone.
These are going to be driven by a Marantz 2325 which puts out a hefty 125wpc (I'm also restoring that for my buddy). So power handling is a consideration. The Misco is rated at only 50w.
Was looking at:
https://www.parts-express.com/visaton-w250s-4-10-woofer-with-treated-paper-cone-4-ohm--292-574
Or
https://www.parts-express.com/peerl...8cp00-04-10-paper-cone-woofer-4-ohm--264-1598
Both seem to be in the right neighborhood in terms of parameters, though they both recommend dual ports. Not as high of power handling as I would prefer, but still better than the Misco. And a bit less coin than the factory 10" drivers from ESS, which would necessitate some reconstruction of the cabinet for secure mounting.
Any thoughts?
What's the power rating on the tweeters, anyway?

Also, while I identified that the crossovers were basically the same, they are actually both modified, and in different ways. I can't really make sense of what the previous owner was trying to do, so, those will need to either go back to stock, or be tailored for whatever woofers I end up with.

I really hadn't intended to redesign the whole speaker, but it seems like that's where I've landed.

FIY the Misco will handle all the power the Marantz can dish out. As mentioned, with a 1 1/2" voice coil (same as stock) this is a very conservative rating. You have to understand how power is applied to a speaker coil.
Modeling programs look at power being applied evenly at all frequencies-music isn't like this.
Plus the crossover absorbs power as well.
If you still have concerns, contact Misco-a very friendly bunch!

 

[automojo]

Looking at this again, trying to keep it less costly and more simple, I'm first in the camp of re-foaming the woofers you have and trying them. That's also been suggested in a previous post. They may sound more similar than you think. Even if they look different, the company would have tried to maintain the same basic sound. Then you have no cabinet mods.
I don't have the exact power handling of the Heils and I can't say that I've seen it printed anywhere. I have a pair of Heil Elites which is just a Heil and a crossover used as an add on tweeter. This is fused with a 3ag one amp fast blow fuse. At one point in time I think ESS had a separate in line fuse for the Heil in one of the Monitor or AMT3 cabinets. I believe this also was a 1 amp fast blow. So, if you feel compelled to protect the Heil, You can certainly add an infuse behind the Heil with a 1 amp fast blow. But as original from the factory, the Heils were not separately fused in this system. The entire system is fused with a 2amp fast blow fuse. I would say though for your friends benefit, new diaphragms are in order. I have not damaged the Heils in my 2 pair of them, nor have I blown the fuses. But I run tone controls flat. Who knows what your friend is going to do.
I'm not much help on crossovers. There are others here on AK that are. You can down load the Xover schematic for free on the ESS website. There is also a Service Manual you can down load on that site as well. It tells you how to replace diaphragms on the various Heils. The Service Manual has an intro page about amplifier power that is an interesting read. Its one of the reasons why I have always believed you can never have too much power.
Unfortunately, a matched pair of 1 Xovers that had been recapped just sold on Ebay not unreasonable cash.

The early 4 coil AMT 3's had a 2 amp fuse on the mid-and a 1 amp fuse on the Heil (open fuse holder on top).