Greetings! First time post and I am happy to have stumbled upon this thread!
I also grew up with Ess in the house and had to have a pair upon buying my first house. My old man has a pair of amt 1b's & I was able to find a pair of 1a's for a reasonable price and in respectable condition with new foam surrounds and radiators, but otherwise original.
Unfortunately, the sound is not quite as sweet as I remember. The Heil seems quite a bit loud compared with the bass. Particularly in the mid range and the mid sounds a bit off. Kind of overly filtered and tinny. Vocals can sound a bit naisaly or raspy depending upon the source. The best sound I can dial up is with the brilliance dial at about 9:00 (far outside the optimum range) and a 3db cut to the mid on my preamp.
Also, one of the brilliance dials crackles and cuts out while adjusting, and if the midrange selector switches are functioning, it's so subtle I can't notice.
Ess will refurbish the xovers, but they only test and replace anything off factory specs. They're maybe 40 years old, so I'm considering replacing them all myself.
It looks like some of the values are hard to find and I would need to place multiple caps in parallel to get proper values. Also, I wasn't sure if I should "upgrade" to polypropylene or stick with electrolytic. Any suggestions?
Welcome!
You've touched on two of the biggest complaints against the AMT, that it runs faster than the low frequency driver, and that it has no mids. I'd recommend leaving the mid cranked up full blast for psychological reasons, but I leave my high frequency knob in the just a little bit more than barely-on on. I also listen to two-channel in Direct mode with no other tone controls.
Something I've noticed a lot in the past few months with my basically new speakers is that they sound like crap for a good 15 minutes if I haven't listened to them in a while. This was apparent to me recently when I plugged them back in after listening to a "crap" brand of speakers that I've been refurbing and which have a completely different style and approach to sound. But after that 15 minutes, there comes a time when I stop thinking about the sound and the music just seems to float in, and when the AMT better blends with the low frequency driver. So, give it a few minutes to warm up.
Next, get some De-Oxit and clean up the L-Pads.
If you've gone through this whole thread, you'll see my rebuilt crossovers. They're basically factory spec with new Dayton caps, but I had to fabricate a new board to make it all fit. And by that point I just went crazy with new terminal barriers and custom-braided wiring. Now that I'm running the AMT Monitor crossover, I'm going to make these 1a crossovers available on the sale site, but hey, this isn't a marketplace thread, so just saying that I think this crossover is worth the effort and cost. If you can solder, you can do it yourself.
You can find 50+ pages of schematics here, though there is some model variance even between speakers with the same name:
http://esslabsusa.com/download/
I'd really like to get a dsp for these. I've tried them in different rooms and was blown away with the huge difference in performance. They worked best in the bedroom along the short wall with carpet, and a mattress. Much tighter bass. I've added a rug and some furniture to the front room where I have them now, but it's not quite as good as the bedroom. I'm hoping the dsp can make even more improvement and possibly bypass the xover and go active in the future.
With a rear-firing passive radiator, you will get bigger, boomier bass closer to the wall. The bass will lean out the further from the wall you get. As one who successfully went active with this speaker and the ESS 2241 Active Electronic Crossover, I can say that that is a fine idea.
If you ever do keep us informed. I've thought an L pad for the tweeter might help.
It has two already.