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Old 10th August 2013, 06:30 AM   #1
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Default Transformer confusion

I am a bit confused, I have seen where people say to use a Push Pull output transformer for driving an ESL and I have seen where people say it doesn't work. I guess my question is, I have some 8k push pull transformers laying around from el84 push pull amplifiers, will these work for driving ESL speakers? If so, up to what size panels will they drive? Any help is appreciated.
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Old 10th August 2013, 08:36 AM   #2
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CONSTRUCTION Format: Floor standing dipole with 3 fixed tilt black Type Multiple Electrostatic Drive Membranes Membrane Ultra Low Mass (0.5gm) Tensioned Film No. of Panel Elements 6 Time Delay Progressive Concentric Rings Chassis Structure Heavy Duty Composite Aluminium / Steel ACOUSTIC PERFORMANCE Maximum Output 2 N/㎡ at 2m on axis Sensitivity 1.5 mbar per volt referred to 1m (86dB/2.83V RMS equivalent) Impedance 8 Ohms nominal Impedance Variation 4 - 20 Ohms Maximum Input Continuous input voltage (RMS): 10V Programme Peak for undistorted output: 40V Permitted peak input: 55V Frequency Reponse 32Hz - 21kHz (-6dB)
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Can't think why they won't work. The ESL requires voltage to make it work, an amplifier supplies exactly what it needs. Maybe mistakenly the variable impedance is making them think it is not suitable, in which case that is wrong assumption. If that is the case, why did Quad produce valve amplifiers to drive their ESL's?
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Last edited by JonSnell Electronic; 10th August 2013 at 08:37 AM. Reason: Wording error
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Old 10th August 2013, 08:40 AM   #3
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Tube OPT's will work to drive ESL's however you may not get the best performance out of them Depending on several factors.
Having a high self (parasitic) capacitance is one of them for some/most models.

The second and foremost thing to watch out for is that tube OPT's aren't designed for the very high voltages (2-5Kv and higher) required for a good performance system.

My very first ESL transformers were a pair of 6V6 pp OPT's from an old RCA chassis that I had.

They were small but worked well until one day they stared to breakdown form the very high bias voltages of about 2Kv to 6Kv or more that I was applying.
They eventually became useless with internal arcing and shorted turns causing much nasty distortions and finally they quit working all together.

This was in 2003/4 and I had to put my ESL projects on the back burner for a while until I could find or build some suitable transformers.
Here are some pictures of those panels,

Material for ESL

During the next 4 years many other life situations got in the way of progress as well, But in 2008 I had ran across a sweet deal from Parts Express for some 200watt power toroidal transformers for cheap, so I got 10 of them to build some amplifers.

About a year later I was reading the threads and come across one that suggested that they might work well and that a few people have tried it with good results.

In 2010 I got back in with the DIYAudio community and discovered that many were using them so I decide to give my cores a try.....And They worked!!!

The rest is history from there (Febuary of 2010) and I was able to revive my original panels that I had built and enjoyed only for a short time in 2003.

My whole story and the rebuilding and testing of my panels are well documented in several threads.

Mostly I have been documenting the operation and requirements of the mysterious device since then as well.
And that thread starts here,

Material for ESL

Material for ESL

and continues here,

Step-up transformer design

Since then I have been learning more myself and trying to teach other as well as to how and why they do what they do.

My honest suggestion would be to save them for a tube amp build or you can use them to power a set of DIY ESL Headphones.
ES Headphones only require about 500V to 1200V of bias and this should be well within the safe limits of the transformers construction and also give you a Fullrange operation for them.

I used the EL84 OPt that I have to power this micro driver and it sounded incredible!!!
Here are pictures of the driver as I whipped up in two days,

Material for ESL

Material for ESL

Second assuming that they have 8 ohm secondary's with 8k plate windings equate to only a 1:31.6 step-up transformation ratio and if it has a 4 ohm tap then it only increases to a 1:44.72 step-up ratio.

This is not be enough to adequately drive a decent sized panel.
And even less should you decide to build smaller desktop sized ones like I have been designing.

Although it would make sound, You would be hard pressed too not have to turn up the amplifier to get a full filling sound out of them.

This would cause an over voltage situation and the eventual breakdown of the transformer, Thus destroying it.

Typically it takes about a 1:70 to 1:120 ratio, or more if it is a smaller panel as they have less surface area, to properly drive an ESL system.
So you would have to use two of the ones that you have now just to make it work right.
And that still doesn't say what the transformers absolute limits are.

You would be better off getting a pair or two pair of Antek or other suitable 240v/6v toroid transformers for a whole lot cheaper than what it would cost to replace just one of the EL84 OPT's!!!

I hope this helps you.

Cheers!!!
jer

P.S. Another good description I just posted can be found here,

The Valorous Amp - A modest aggregation of pass inspired ideas

Last edited by geraldfryjr; 10th August 2013 at 09:02 AM.
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Old 13th August 2013, 11:13 PM   #4
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Default Transformer Breakdown ...

Typically the Insulation Resistance on an Audio Power Transformer is only 1,500 Volts - the Tube side typically operating at less than 500 volts and the Loudspeaker Side less than 100 volts. So while operating them in reversed fashion and applying Bias Voltages over 1,500 Volts to the Center Tap to polarize the panels seems plausible, the low Insulation Resistance on the windings allows breakdown as jer experienced. One would have to rewind the transformer with wire with a much higher Insulation Resistance to make that work, or use one designed for ESLs in the first place ...
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Old 14th August 2013, 04:08 AM   #5
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Thank you everyone for all of the information, I guess I will be saving those P-P OT's for another amp project.
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Old 14th August 2013, 08:59 AM   #6
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Also a power transformer is not suitable for a full range esl. The step-up is usually to low so only unsegmented high capacitive esl units can be used. For me this is a dead end because i don't like this extreem directive units.

Quote:
Originally Posted by torroid88 View Post
Typically the Insulation Resistance on an Audio Power Transformer is only 1,500 Volts - the Tube side typically operating at less than 500 volts and the Loudspeaker Side less than 100 volts. So while operating them in reversed fashion and applying Bias Voltages over 1,500 Volts to the Center Tap to polarize the panels seems plausible, the low Insulation Resistance on the windings allows breakdown as jer experienced. One would have to rewind the transformer with wire with a much higher Insulation Resistance to make that work, or use one designed for ESLs in the first place ...
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