"new" ESS amt unpack

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#104
Nelson Pass said:
You would want to talk to my wife. She ended up in QA and R&D
watching over the diaphragms. Back then all sorts of black magic was
being employed to keep the reject rate down to a reasonable level. To
their credit, management did not yield to the temptation to ship sub par
product.

She was the keeper of the golden diaphragms, and thus quite popular,
in addition to her already considerable charm. She also developed a
number of ad hoc fixes to diaphragms that got the yield up.

:cheers:
Click to expand...

I am always in for a good story. Given that the big ESS AMT even today is considered a top end tweeter, it must have been mind boggling to have this kind of technology in the seventies... 😱 😎

Fedde
 
#113
Nelson Pass said:
You would want to talk to my wife. She ended up in QA and R&D
watching over the diaphragms. Back then all sorts of black magic was
being employed to keep the reject rate down to a reasonable level. To
their credit, management did not yield to the temptation to ship sub par
product.

She was the keeper of the golden diaphragms, and thus quite popular,
in addition to her already considerable charm. She also developed a
number of ad hoc fixes to diaphragms that got the yield up.

:cheers:
Click to expand...

I am afraid they certainly could do with some help from her again! 🙂
As much as I like these units - the consistency on the newer builds I have here - based on 4 units and so far 3 membranes isn't particularly good.
Magnet polarity swapped on one unit,
some membranes turned upside down/foil side.
Folds sticking together due to glue, partly shorting out some of the membrane
My new spare membrane had 5.5 Ohm resistance
The protective net on front and back of the units is sticking onto the membrane (glue) on some units and not on others - I expect that the membrane should be able to move freely.

When they work and the polarity is right - they are truly great though 😉
 
#114
A little anecdote OT.
Here in Argentina I worked with the official Ess importer, (1970s) sold hundreds, all the models that were made in those years were brought in. It was a huge listening / exhibition room, Ess had even sent a huge pair of AMT6s ...... with a power amplifier made by them .... which didn't last long, those beasts gulped a lot of watts, and maybe they had a very low impedance curve ...
But what can I say about the sound after so many years? I think the correct description that comes to mind would be "too transparent". For my taste
Perhaps the problem would be the static charge accumulated on the polyester carpet in the huge living room ? 😀
On "those" special (very dry) days customers wandered around the room charging themselves with static electricity and when they touched the metal fronts of the equipment, they jumped back from the discharge!
Yes, maybe we should have put a warning on a sign ......
And the static discharge was directly proportional to the distance traveled, I myself experienced very unpleasant shocks ...
 

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#115
Nelson Pass said:
You would want to talk to my wife. She ended up in QA and R&D
watching over the diaphragms. Back then all sorts of black magic was
being employed to keep the reject rate down to a reasonable level. To
their credit, management did not yield to the temptation to ship sub par
product.

She was the keeper of the golden diaphragms, and thus quite popular,
in addition to her already considerable charm. She also developed a
number of ad hoc fixes to diaphragms that got the yield up.

:cheers:
Click to expand...
Hi Nelson,

I would like to get back on your offer... (though I could not send a PM, hence the public address). I recently found that one side of my (Heil) AMTs sounds quite different from the other side. One side (normally the back side) sounds more dull, the other side more bright & clear. Is there any explanation for this given its construction? One of my diaphragms was mounted wrongly I think, but changing the polarity does not fully fix its response. Only a flip does.

Best regards,

Fedde
 
#116
Fedde,
I think you are already on to the problem.
  • Check and compare the magnetic poles on your units, are the magnets oriented "the other way round" on one of them? (basically one could argue whether it's the magnet or the entire housing with the ESS logo that is turned 180 degrees)
  • Measure the impedance of your units, do they match? if some folds are stuck together then part of the conductor might be shunted out and the impedance will be lower.
  • Measure the acoustic response, and pay attention to the phase response, this must be identical (not just within 45 degrees) on the units or the polarities are wrong.
  • Even if the impedance is roughly the same approximately 3.8ohm +/- Check if any of the folds are stuck together - I have had this on nearly all mine, as the glue used is a type that does not dry out but stays sticky
If I get to it I will upload some pictures...
But there are several webpages diving into the design
https://www.precide.ch/eng/eheil/eheildetails.htm
 
#117
Norgaard said:
Fedde,
I think you are already on to the problem.
  • Check and compare the magnetic poles on your units, are the magnets oriented "the other way round" on one of them? (basically one could argue whether it's the magnet or the entire housing with the ESS logo that is turned 180 degrees)
  • Measure the impedance of your units, do they match? if some folds are stuck together then part of the conductor might be shunted out and the impedance will be lower.
  • Measure the acoustic response, and pay attention to the phase response, this must be identical (not just within 45 degrees) on the units or the polarities are wrong.
  • Even if the impedance is roughly the same approximately 3.8ohm +/- Check if any of the folds are stuck together - I have had this on nearly all mine, as the glue used is a type that does not dry out but stays sticky
If I get to it I will upload some pictures...
But there are several webpages diving into the design
https://www.precide.ch/eng/eheil/eheildetails.htm
Click to expand...

Thanks for the good advice Norgaard. I did not consider the scenario that the magnets are oriented wrongly yet, but it looks they are. I have my left AMT currently flipped and in this configuration the magnetic poles are the same left-right! So you could conclude that the only thing that is wrong now is the location of the logo...

I also made some (somewhat rough) nearfield measurements, including EQ and crossover filter. I repeated them five times front side and back side. Distance is <0.5cm, center of AMT, USB mic Umik1 hold by hand. Take them with some salt, but you can clearly see a different spectral behavior between the sides...
EssAMT.png


Fedde
 
#119
fedde said:
I also made some (somewhat rough) nearfield measurements, including EQ and crossover filter. I repeated them five times front side and back side. Distance is <0.5cm, center of AMT, USB mic Umik1 hold by hand. Take them with some salt, but you can clearly see a different spectral behavior between the sides...

Fedde
Click to expand...
I wanted to do a comparison measurement but I am on a different system so it does require quite some moving around, and I haven't found the time for that yet. - Sorry for the super slow response!
I do however not recall these dips from when I did a manual spinorama measurement on my OB's
Back reflections from the microphone holder ;-) is another thing to take into account. Did you spot any folds stuck together on the one (back)side of the membrane? The white grid in front of the membrane on either side is typically stuck in place also - which must have either a damping effect or potentially generating rubbing noises, not that I have been able to pinpoint any issues - yet....
Looking at the peaks between 7 and 9k the crossover does not work well at all as implemented. As the ESS is ruler flat on the impedance except for a very small curl at Fs, I would not expect to see such a poor stop band performance - only the ESS connected at the measurements?
 
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