One ESL completed - disappointed..

[bentl]

Hi,

my first attemt of building an ESL is "completed" and tested..and failed.

The reciepie is as follows:

1000 X 350 X 2mm perforated, powder coated steel plates, 48% open
6my mylar, Elvamide coated
2mm plastic spacers, epoxied to stators and mylar. (Epoxy sucs, will use cyanoacrylate next time)

Power supply: EMCO G60r power module capable of 6kV


Transformer:
Test 1: 50 Va EI-transformer 2 X 115v primary 2 X 6v sec hooked up in reverse with 2x6 in parallell and 2x115 in series.

Test 2: 2 of 50 Va toroid-transformers 1 X 115v primary 2 X 6v sec hooked up in reverse with 2x6 in parallell and 2x115 in series.

Both test gave a faint sound. Measured about 25v between the stators.

Tried with polarizing voltage negative to diaphragm first, then reversed.
Same result, almost no sound.


I have no idea what could be wrong, but the dissapointment is huge!

Regard (regrets?)

bent

[bolserst]

Originally Posted by bentl

Hi,

my first attemt of building an ESL is "completed" and tested..and failed.

The reciepie is as follows:

1000 X 350 X 2mm perforated, powder coated steel plates, 48% open
6my mylar, Elvamide coated
2mm plastic spacers, epoxied to stators and mylar. (Epoxy sucs, will use cyanoacrylate next time)

Power supply: EMCO G60r power module capable of 6kV


Transformer:
Test 1: 50 Va EI-transformer 2 X 115v primary 2 X 6v sec hooked up in reverse with 2x6 in parallell and 2x115 in series.

Test 2: 2 of 50 Va toroid-transformers 1 X 115v primary 2 X 6v sec hooked up in reverse with 2x6 in parallell and 2x115 in series.

Both test gave a faint sound. Measured about 25v between the stators.

Tried with polarizing voltage negative to diaphragm first, then reversed.
Same result, almost no sound.


I have no idea what could be wrong, but the dissapointment is huge!

Regard (regrets?)

bent

With such a low measured output voltage, my guess is that your secondaries are wired out of phase, so the voltages are canceling each other. Try running a test with just one of the transformers applying 6 volt input to the paralleled primaries. Then measure each of the secondaries separately and make sure you are getting ~ 100 Vac. Then hook the two secondaries in series measure the output. If you get 200 Vac or more, you have them hooked up properly, if not swap the ends of one of the secondaries.

Once you have each of the transformer secondaries putting out 200 Vac, then hook up both transformers together, secondaries in series, all the primaries in parallel. You should still be getting ~ 200 Vac from each of the transformer, and ~400Vac across both. If you get 200Vac across each, but almost nothing across both, swap the polarity on one of the set of transformer primaries.

You didn't mention it specifically, so I'll add the comment to hook one end of your HV supply to the diaphragm, and the other end to the center point of your series connected 4 secondaries.

Good Luck!

[chinsettawong]

Hi Bentl,

Don't be too pessimistic. Your amp power might not be enough. What kind of amp do you use to drive the ESL? What is the bias voltage you use?

About glue, I find contact cement to be extremely good for gluing spacers to the stators. I use thin double sided tape for gluing my diaphragm to the spacer. It works very well for me.

If you want to, I can introduce a local transformer maker in Thailand to make a couple of transformers for you. I find their price and quality to be very good.

Wachara C.

[Calvin]

Hi,

I´d think the same direction as bolserst and check if prim and sec. windings are wired correctly. If You drive just 1 primary and volume rises it´s one wrong primary, if not interchange one of the secondaries.
If its nott the tranny, the source of fail should be found around the bias-supply. A failure of the HV-Bias-supply is unlikely, but the diaphragm connection might not work, so it won´t charge up.
Hope You haven´t glued everything together? Because You can test each stator alone before putting everything together.

jauu
Calvin

[bentl]

Hi, I use a 2x 52w class A tube amplifier

the polarizing voltage should be about 4000 volts I have not tested max yet!

Thanks for your replies I will reconfigure the transformers and try again.

Regards

bent

[bentl]

Hi, I have rewired the transformers and get approx 60X voltage rise on the output.

Applying the polarizing voltage does not affect the sound level, so I guess there is a problem with charging.

Either the coating (Elvamide) or the copper foil tape used to electrically connect the diaphragm.

I wil buy a better multimeter tomorrow and see if I can measure electric contact on the diaphragm.

Regards,

Bent

[bentl]

I'll be d@mned!!

After half an hour of faint sound the speaker plays louder and louder....and louder!

Seems like it takes some time to charge the diaphragm!

Great!!

[Kontra]

Originally Posted by bentl

I'll be d@mned!!

After half an hour of faint sound the speaker plays louder and louder....and louder!

Seems like it takes some time to charge the diaphragm!

Great!!

congratulations.
increase the volume takes the same number and volume decline.
your coating 10 * e10
excellent result!
ps: next step - direct drive amplifier

[bolserst]

Originally Posted by bentl

I'll be d@mned!!

After half an hour of faint sound the speaker plays louder and louder....and louder!

Seems like it takes some time to charge the diaphragm!

Great!!

Do you have your copper foil contacting the diaphragm in just a small area?
If so, you might improve the diaphragm charging by running the copper foil the full length(top to bottom) on both left and right sides of the panel.

[alexberg]

Originally Posted by bentl

Hi, I have rewired the transformers and get approx 60X voltage rise on the output.

Applying the polarizing voltage does not affect the sound level, so I guess there is a problem with charging.

Either the coating (Elvamide) or the copper foil tape used to electrically connect the diaphragm.

I wil buy a better multimeter tomorrow and see if I can measure electric contact on the diaphragm.

Regards,

Bent

Dear Bent,
the contact appeared to be of great importance and not only when you measure coating resistance.
Coins or thick (0.05mm) copper strip do not provide reliable contact, IMO.
Sprayed grapfite from aerosol can seems to be much better, just make an appropriate stencil.
Another thing to consider: it appeared that corona discharge easily develops at the edges of the contact strip, rendering your measurements quite inaccurate.

By the way - have you tried to do scotch test i.e. to see if the coating peels away by Scotch tape?

Congratulations,
Alex