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Old 1st May 2004, 10:59 AM   #1
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Default ESL Problems after thier first run

After the first run of my ESL (I have another but only one transformer wound atm) too my delight, I actually got a sound
It was only faint as my transformer was arcing itself into destruction.
The output level is the same with and without the power supply connected. Input to the transformer is approx +- 18v music (not tones).
Just looking at the transformer the secondary winding's were arcing through the teflon tape (plumbers sealing tape) into the rest of the windings.
The transformed is core out of a 8 ohm/100v transformer rated to 20kHz 60w. I unwound it and rewound the primary as the same 8 ohm and wound a 1000 turn, centre tap and another 1000 turns. The primary i think was 13 turns. I just rewound what it originally had. All was wound with normal magnet wire. (just from looking) It was a 1.5mm primary and the secondary is just a bt thicker than human hair, I have no idea of gauge since its to small to measure and was given to me by my boss.
I'm going to have to rewind the whole thing anyway, can anyone tell me how i could improve this?
At work, I've seen a black coated winding wire that is fairly thin and comes in a 33m roll. It looks alot tougher than enamel coated wire.
Thanks for your help
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Old 1st May 2004, 11:07 AM   #2
316a is offline 316a  England
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Default Re: ESL Problems after thier first run

Quote:
Originally posted by fr0st
After the first run of my ESL (I have another but only one transformer wound atm) too my delight, I actually got a sound
It was only faint as my transformer was arcing itself into destruction.
The output level is the same with and without the power supply connected. Input to the transformer is approx +- 18v music (not tones).
Just looking at the transformer the secondary winding's were arcing through the teflon tape (plumbers sealing tape) into the rest of the windings.
The transformed is core out of a 8 ohm/100v transformer rated to 20kHz 60w. I unwound it and rewound the primary as the same 8 ohm and wound a 1000 turn, centre tap and another 1000 turns. The primary i think was 13 turns. I just rewound what it originally had. All was wound with normal magnet wire. (just from looking) It was a 1.5mm primary and the secondary is just a bt thicker than human hair, I have no idea of gauge since its to small to measure and was given to me by my boss.
I'm going to have to rewind the whole thing anyway, can anyone tell me how i could improve this?
At work, I've seen a black coated winding wire that is fairly thin and comes in a 33m roll. It looks alot tougher than enamel coated wire.
Thanks for your help
Hello ,
You could always use a mains toroid with split primaries . These work rather well considering their cost

cheers

316a
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Old 1st May 2004, 01:29 PM   #3
SY is offline SY  United States
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The classic approach is a tube output transformer turned backwards.

Check the actual insulation voltage rating for whatever wire you're considering. If you know someone who can do Hipot testing, it would be worthwhile to do that before dropping the tranny into your system.
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Old 1st May 2004, 02:58 PM   #4
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I was thinking of ordering a proper core from Farnell that I can wind specifically for the task rather than a rewound 100v core.
What type of core (EI, torroid, planar etc.) would be best and which material?

Also a friend surgested that an enamel epoxy (or equivalent if that doesn't exist) to cover any cracks in the enamel when winding. Mica would also be a perfect insulator between layers.
I think a mains torroid wouldn't be well suited to driving the esl's since there originally designed for 50/60hz operation and even a 240v/9v tranfo is only a 1:27 ratio.

Thanks
Matt
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Old 1st May 2004, 05:09 PM   #5
316a is offline 316a  England
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Quote:
Originally posted by fr0st
I was thinking of ordering a proper core from Farnell that I can wind specifically for the task rather than a rewound 100v core.
What type of core (EI, torroid, planar etc.) would be best and which material?

Also a friend surgested that an enamel epoxy (or equivalent if that doesn't exist) to cover any cracks in the enamel when winding. Mica would also be a perfect insulator between layers.
I think a mains torroid wouldn't be well suited to driving the esl's since there originally designed for 50/60hz operation and even a 240v/9v tranfo is only a 1:27 ratio.

Thanks
Matt
Hello ,
50Hz operation ? A got -3dB at 44kHz from a 50VA Talema unit . A 115/115:6/6 mains toroid with the secondaries paralleled should do the trick and get you up and running at least . Currently using a 115/115:55/55 mains toroid as a stepup hanging off my valve amp's output stage anodes via teflon capacitors driving my ESL treble panels . So far nothing has fizzed , crackled , arced or exploded

DISCLAIMER
It's a small breadboard setup driving a small panel , unknown how well toroids will cope swinging the several thousand volts a larger panel will require

cheers

316a
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Old 2nd May 2004, 05:47 AM   #6
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I just ran across another problem.
I connected the esl to a 8 ohm, 100v transformer for comparison to my own and after a bit of playing I discharged the bias supply and the esl kept playing?
Even with the centre tap disconnected the esl's are still able to play music at the same level as before. I've tried reversing the bias polarity but it still made no difference.
The supply is definately working (I've touched it and shorted the output to ground to see a huge spark) I'm unsure of how it's managing to work....
The transformer is getting warm and the amp is turned 3/4 of the way up (distorts above this) on a lm1875 gainclone. The transformer has a 0,2 ohm,4 ohm, 6 ohm and 8 ohm primary and a 0, 10w, 20w, 30w and 60w secondary. I'm currently using the 2 ohm primary and 0, 30w (centre tap) and 60 on the secondary.
Can anyone explain this?
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Old 2nd May 2004, 06:34 AM   #7
1audio is offline 1audio  United States
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Default ESL Panel Charge

If your panels are a decent design the surface resistance is very high. Once the charge is on the panel it will stay there for quite a while.

And an ESL will make sound with no supply, It will be mostly second harmonic however.

Good ESL transformers are very difficult to make. The turns ratio is high, the insulation between turns needs to be large. Also the dielectrics all affect the performance.

The breakdown you had was most likely from adjcent turns having too much voltage between them. Probably layer to layer. The breakdown voltage decreases with frequency so the 50 or 60Hz breakdown will not predict performance at high audio frequencies.
-Demian
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Old 2nd May 2004, 10:37 AM   #8
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Quote:
If your panels are a decent design the surface resistance is very high. Once the charge is on the panel it will stay there for quite a while.

And an ESL will make sound with no supply, It will be mostly second harmonic however.
I got the other panel connected up (same setup) and ran it without the bias connected at all and it didn't run so you were dead on. Thanks

When i wound my transformer I think the problem I had was the insulation between layer. Teflon tape wasn't the best idea I think
I havn't looked to hard about this but the enameled wire farnell sell is rated at 1500v rms insulation breakdown which would definately explain my arcing problems.
The plan sofare is to rewind the primary, insulate with self almagamating or electrical tape, wind half a secondary, insulate again, other half, centre tap, insulate... etc.
Can anyone surgest anything else that would help?
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Old 2nd May 2004, 04:58 PM   #9
1audio is offline 1audio  United States
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Default Transformer Winding

There are two real tricks to making the transformer work I believe. First is the way you wind the layers. There are a number of ways to optimize them. The Tesla coil guys have this down. Second, the interlayer insulation. I believe the paper or special film (Kapton?) is critical. The wizard at Magnequest wrote about this with some tips. Look here: http://home.zonnet.nl/horneman/ml/mklf.htm
He has more on the web as well.
-Demian
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