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Driving ESL transformer more efficient on SS-amp
Driving ESL transformer more efficient on SS-amp
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Old 29th October 2017, 11:56 PM   #1
Joshcpct is offline Joshcpct  Germany
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Default Driving ESL transformer more efficient on SS-amp

Hi guys

Problem: My ESL is unefficient and eats amps for breakfast.
Each amp makes huuuuge difference in soundquality and quickly clips.
They also roll off in the highs, and when I EQ it, the amps hate that even more It quickly sounds stressed above 90dB, and the 10dB boost in the highs >10k definately make it a lot worse.

The least stressed so far were Fostex Laboratory amps. But dont sound not perfect in general (clearity, stagesize, dynamics) - 300 Watts.
Best sound was a Parasound 806 but suffers lot from stress when louder (80 Watts).
Just for fun an old cheap Technics SEA1000 clips already on lowest volume

So finally I drive it on 2 Parasound HCA 2200 MKII.
It is a good balance between previous favorites, though not perfect.


Now, the ESL comes with a serial resistor of 6.7R (10%) MOX 10 Watt.
The efficiency is pretty low, as usual.
Thats what i just measured:
Click the image to open in full size.

the DC meter sais 0 ohm without the serial R, connected to the transformer.
Lowering the resistor from 6.7 to 4.7 doesnt really increase much the audible loudness but clearly the highs, sounds much brighter. Which sounds logical considering the impedance in the highs.

So, id love to skip that resistor but the Parasound wont like that
I guess 2-2.5 R they should survive. That should boost the highs many dB and I could skip the EQing.
But... I can climb from 380 to 1000 Watts if i bridge the amps (got 2).
In that case Id need to increase the serial resistor to double, which leaves me with no big benefit other than heating the resistor

Do you think I could instead use bridging, plug a 4.7 R and parallel a 10uF cap + 1-2 Ohm R. ??
That would limit the DC-R to amp friendly level, but lower the highs AC-R to a mean minimum, enabling the juice to flow....

What do you think?

cheers
Josh
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Old 30th October 2017, 08:18 AM   #2
Joshcpct is offline Joshcpct  Germany
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If u got confused by all the blabla ...
What i meant was this
Click the image to open in full size.

Asking if that wouldn’t blow the bridged amp and benefits higher spl in highs?
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Old 30th October 2017, 09:11 AM   #3
tyu is offline tyu  United States
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Hi....for years I have read this..ESLs need BIG power to work an give full output!..only ESL that I have seen like this were Sound labs...I had one pr of older SL A3 ...sold them after hearing my First Acoustat Xs....
To day in my room 18'x25'x13' I have a pr of Acoustat 2+2 Martin logan CLS an Acoustat Spectra 11....all can be ran off 60 tube watts, with out any stress...great top end well in to the upper 90dbs...
On my CLS I have only a 1ohm 20 watts on the pos input with a 1ohm-10mf cap in a zobel on the 1ohm...like the zobel you have on your 4,7...sounds great an vary ezey to drive...

What ESL do you have?
What bias volt do you have on your pr ESL?....sounds like it maybe vary low...ck it!

Last edited by tyu; 30th October 2017 at 09:13 AM.
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Old 30th October 2017, 09:56 AM   #4
Joshcpct is offline Joshcpct  Germany
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Hi tyu
Well its not exactly a zobel or. But similar effect though.
I heard some use a normal zobel to eliminate the UHF resonance peak of the transformer beyond 30k up. But i cant measure mine higher than 20k. Would be considerable as my amp got xtreme negative feedback (damping >1000).

I got a Capaciti EL160, former german small brand. 20x120cm longthrow foil.
I guess it’s a lil easier to drive for low feedback tube amp with more headroom / soft clipping.
But the total volume wont exceed the 90db spl much.
I prefer SS to get around 100db and also personal preference.

So you also bypass the resistor with a cap to get more HF efficiency??
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Old 30th October 2017, 08:49 PM   #5
Calvin is online now Calvin  Germany
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Hi,

when they are in good working condition Capacitis are quite efficient and not that difficult to drive.
After Your description I assume a faulty condition of the panels.
Could be a major loss of polarization voltage (polarzing supply, membrane contact).
Since You seem to have tried more and more powerful amplifiers it might even be that the audio transformers suffered from internal flashovers.
I'd suggest You measure the polarizing voltage of the supply and membrane and the output voltage of the audio transformers to see if the electronics is still ok or if its faulty.

jauu
Calvin
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Old 30th October 2017, 09:05 PM   #6
Joshcpct is offline Joshcpct  Germany
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Hi Calvin
Can you tell me in a nutshell where, how and desirable-values?
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Old 30th October 2017, 09:17 PM   #7
bentoronto is offline bentoronto  Canada
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Driving ESL transformer more efficient on SS-amp
+1 for Calvin's post.

The first fix may be just raising the bias. I have big spacing and run over 7kV. Do you have a DIY high voltage probe?

ESL panels, as seen through a transformer, are a horrible load. In my recent efforts, I tried great many networks but ended up with just enough resistance to keep my large amps* happy but not enough to screw up the FR signal too badly into the transformer.

So I'd start by more closely examining the signal reaching the panels downstream of the transformer if you can or at least reaching the transformer "primary".

Can't say as I believe any decent amp sounds different than any other, providing they are working with loads they can manage.

B.
* even my big amps sometimes go into over-load protection north of 8kHz if doing loud REW sweeps; 1980's Kenwood Basic class G capable of hundreds of watts into low loads
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Old 30th October 2017, 11:19 PM   #8
Joshcpct is offline Joshcpct  Germany
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Well i hope im just too sensitive being used to horn speakers - not that the ESL are broken.

I dont have the equipment, need to ask a friend & engineer for a visit.
So, anyone knows how much volt they should have?
Think its adjustable?
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Old 31st October 2017, 09:11 PM   #9
Joshcpct is offline Joshcpct  Germany
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K something real to grab. Measured the Capaciti with 2.83volt amp output in 1 meter distance.
Lot of room incl therefor 1/3 oct smoothed.

Click the image to open in full size.

It looks more or less like I expected. But if you say they should be easy to drive, there are def. 5-10dB missing. Or ??
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Old 1st November 2017, 07:42 AM   #10
Calvin is online now Calvin  Germany
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Hi,

don't know the actual values but the polarizing voltage should be >3kV, probabely around 5kVdc.
The ratio of the audio trannies will be somewhere around 1:100 to 1:150
The amplitude response really looks too low in volume by ~5dB.
Could be a serious loss of polarization, as the HF response falls down too much after my taste.
Btw. the 1m measurement isn't used so often with strip like speakers .... gives almost always bad results.
You better measure the panel twice, once in very close proximity ~5-10cm (near-field condition) and at greater distance, say 4m (far-field condition).
Don't be astounded to see higher SPLs with the 4m measurement.

jauu
Calvin

ps. Michael Ehrlinspiel once told me that he gave all mashinery and plans to a former employee to ensure servicing of the speakers.
Unfortunately don't I know who that person is and how to contact him.

Last edited by Calvin; 1st November 2017 at 07:46 AM.
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