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ESS amt 1am Crossover Help

Tonewall

Tonewall

Member
I want to recap a pair of ESS AMT 1AM, but here's the catch. A local audio shop in Kansas (Audio Mart) upgraded them back in the late 70's early 80's. I believe these are called Custom Monitor Elites adding a midrange speaker in place of the passive woofer. Anyway, the crossovers are different than the originals and I was hoping for some advice on one particular piece.

Below is the schematic (sorry about the amateur drawing) and a few pictures. Here's my question, I'm not sure if I need to replace the two 50uf caps in series with the exact same setup or can I do something similar with one cap instead of two? If I understand correctly, caps in series half the capacitance but double the voltage. So could I use a 25uf cap as long as the voltage was sufficient?

Also, I assume these 50uf capacitors in series and the 100uf capacitor are less important to the audio path and as such the quality of the replacement capacitors are not as important as the other ones, correct?

Thanks!

ESS AMT 1am schematic.jpg
50uf Caps.jpg
Full Crossover.jpg
ESS AMT Monitor.JPG
 
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That is quite possibly the worst crossover design I've ever seen, am I missing something? 2 bandpass filters in parallel shorting across the speaker terminals?
 
It's possible I missed something when tracing out each wire and lead. I can verify again when I get home today. It does seem odd, that's why I'm asking.
 
Son-of-Vere said:
That is quite possibly the worst crossover design I've ever seen, am I missing something? 2 bandpass filters in parallel shorting across the speaker terminals?
Click to expand...

@Son-of-Vere I did verify that this is indeed how the crossover is wired. Two 50uf (50vdc) capacitors in series with an inductor wired between the speaker terminals

I did a little digging online and found the following info:
"it is safe to place a cap across the speaker terminals in this circuit because of the series inductor. The inductor introduces a rising impedance at the approximate frequency where the capacitor has a lowering impedance, so the inductor prevents the short across the amp. The inductor and capacitor interacting with each other gives an effective steeper rolloff to the driver connected to the network, and protects the amp. So in this case it is a great thing. Take the inductor out, or design it incorrectly, and the amp will go boom."

Does this sound correct?
 
Upon further inspection, I think the bottom cap and coil are shown backwards. The 2 50's and coil may be there to quell the woofer resonant peak. We have a few ESS experts around here, I'd be interested in their opinion.
 
Yeah that's who I was thinking of as well. I may have worded my statement incorrectly. I'm think the notch filter across the terminals would allow flow when the woofer is at it's resonate peak, keeping a steady load on the amp. Usually, the notch filter should be after LC on the woofer. I do not find myself an expert on this type of crossover strangeness, I'm always willing to learn more.
 
I would replace them with the same values-as the circuit was designed
50uf's EL, or Jantzen MKT's are readily available.
Swap out the Sand Cast for Mills or Jatzen Supres.
A .1uf Dueand Bypass on the mid and Heil Caps, with Superior Z's and main caps.
Money well spent!
FIY these aren't Moniter Elites.
Those used a Gauss woofer.
They also had the crossover in a separate box.
These are ESS coils-and the front mid area is fabricated.
And the mid section is just fabricated from the upper woofer baffle cutout.
Decent enough job-but not the same.
 
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And probably modified the crossover to deal with one woofer-vs 2. Normally it should use 2x51uf caps
SO if everything sounds fine-you should be good!
 
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Thanks, @Automofo, I greatly appreciate the information and suggestions. The speakers are from Audio Mart (according to the label on the back) and do have the Polydax midrange, but you're right not the Gauss woofer so I guess they're not Monitor Elites. As I'm looking into recapping the crossovers would it make sense to swap out to Gauss woofers now? Not sure how much better those are than my stock woofers.

If not, just so I understand, swap out the following:

Replace 100uf & 50uf's (the ones in series) with Jantzen MKT's
Replace resistors with Jantzen Supres resistors(I assume 10w)
(This is the part I'm not clear on) Replace the two 8uf and single 50uf caps in the Heil and Mid signal path with Jantzen Superior Z-Caps. I get the 8uf's, but I can't find a Superior Z-cap in the 50uf range.
 
Sure.
I wonder if this is a earlier version-and they sourced the complete cabs from ESS as well as the crossover.
The Elites-from what I recall just used the walnut sides.
I would use Jantzen Superior Z's for the mid and Heil caps.
The bypass caps for the Mids and Heil is a added suggestion.
They are currently on sale for $28 ea @ Parts Connextion.
The Deulunds give you a jump in smoothness and added realism.
Minimum I would use the Superior Z's for the mids and Heil.
IS the 50uf in for sure in series or parallel with the mid/Heil?
If it is indeed series-I would go with a Solen Fast Cap 47uf +3uf/2.8 Superior Z.
The Solen is $27ea
Be aware the Solens are large.
If you do decide to bypass-I would stick with the Heil here-the 8uf.
 
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And MKT for woofers.
I like the fact the are compact and flat on top so you can stack etc.
 
Thanks for the info

Just to give you an image of the crossover label. Also I'm positive the 50uf is in for sure...as it's directly soldered into the speaker wire going to the mid ‍♂️ (See below)

ESS AMT 1am (3).jpgESS AMT 1am (7).jpg
 
But looking-they don't have that value-just use Crosscaps for the woofers. Compact as well.
 
They should sound excellent!
The Polydax-even today is one of the finest midwoofers out there.
Plus your bass is a sealed box.
A win/win IMHO!:)
 
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