esl transformer.

Trannies from old tube amp

There are two types of high voltage transformers associated with ESLs, the high voltage bias supply for the diaphragm, and the step-up transformer that interfaces your amp and the ESL's stators. The cheap trick for both of these is to use transformers salvaged from an old tube amp (push-pull type). For the bias supply, use the power transformer’s B+ winding. You would make a voltage multiplier (stacked diodes and caps) to multiply the high voltage to even high voltages for the ESL bias, which can be anywhere from about 1000 to over 5000 volts.

For the step-up transformer, you use the tube amp’s output transformer “backwards”. You drive the 4 or 8 ohm secondary (now a primary) and connect the former plate taps to the stators. The bias supply goes between the center tap and the diaphragm. Usually you want a step up ratio of better than 50:1, so try to find a high primary Z tube amp. A smaller amp using, say, EL84s might have 8K primaries. If you drive the 4 ohm tap, you’d get a step up of about 45, barely enough, but maybe good enough for getting started.

There are a thousand factors to consider to really do all this right: leakage inductance, winding capacitances, voltage ratings, ratios versus panel designs, etc. I’d suggest you buy books on ESLs by Roger Sanders and Ronald Wagner. You’ll see references in this forum to those two books, which are especially good for beginners.

IT HAS TO BE SAID: THE VOLTAGES USED IN ESLS ARE DEADLY. IF YOU AREN’T EXPERIENCED WITH WORKING WITH HIGH VOLTAGES, CONSIDER FINDING AN EXPERIENCED FRIEND TO HELP YOU. Hate to be preachy, but we’d hate to hear of you getting hurt. We need all the ESL DIYers we can get!
 

SY

diyAudio Moderator Emeritus
2002-10-24 10:19 pm
Chicagoland
www.SYclotron.com
Since you're in the US, you should keep your eyes open for old Dynaco SCA35 or ST35 amps. The output transformers work very well in this application used backwards as Brian described. The bias supply needs almost zero current, so a tube amp transformer is overkill (though it will work fine). A high-voltage supply from an old copying machine can easily be pressed into service.
 
tade said:
I emplore you of the internet!
i am a pooor college student interested in ESLs. i need someone more competent than i to recommend a high voltage transformer to me! i would like for it to be cheap and readily available.


There are no cheap, readily available audio transformers. You must either pay a fairly hefty price, or be very good at scrounging them from an old tube amp (this is getting harder and harder to do these days).

You can buy new audio transformers from any of several sites that advertise on the web. Get output transformers with about a 10k Ohm primary winding and 4 or 8 Ohm secondary winding. The primary must be center tapped or you need to get four transformers. 4 transformers will usually make for more sensitive speakers, so if you can get four, do so. 15-20W transformers will be just fine, even if you drive the speakers with a 200W amp.

The high voltage bias supply should be made using the smallest possible transformer if it is to be line powered. It needs to supply very nearly zero current, so to stay safe, you want a really small transformer. Better yet would be a dc-dc converter that converts a low voltage DC input from a wall-wart up to the required bias voltage (3-5 kVDC). There is a plan for such a supply here:
http://www.rehorst.com/esl

I expect for my panels to be four feet square and with 1/4 inch spacing.

If you mean stator to stator spacing, that should be OK. If you are talking about stator to diaphragm spacing, it is too large and you will not get much sound from your speakers, especially if you use only one audio transformer per speaker.

If your panels will be flat, you will need to break them into smaller pieces. If you try to build a driver that is 4' x 4', the weight of the stators, suspended only from their edges, will behave like a drum with a very low resonance frequency. If you bump the speaker frame with your hand the stators will wobble back and forth for quite a while. This may never be excited by playing music, but it does not give a feeling of confidence about the whole assembly to have parts of it wobbling like that. Also, as it wobbles, it flexes and the diaphragm may wrinkle and make undesirable noises in the process.

I would break a 4' x 4' driver into 4 drivers, 1' x 4', and put some sturdy mechanical support (part of the frame to which they are mounted) between them.

The alternative to breaking the drivers into smaller pieces is to curve the stators. A curved stator is much stiffer than a flat one. This is the reason why Martin Logan curves their stators. Curving the stators creates other problems with tensioning the diaphragm that may be quite difficult to overcome.

I_F
 

wrl

Member
2003-01-07 11:01 pm
USA
Check out www.justrealmusic.com

They aren't really "cheap" but they are definitely less expensive than some other suppliers. They are also very helpful if you have questions about wiring or ESL's in general. I'd recommend calling them.

Also you might want to consider using 1/8 inch spacing rather than 1/4 inch. That way you could use a smaller step up ratio (cheaper transformers) and not sacrifice as much output.

No joke though be careful when working with these.

-Wes
 
Transformer Confusion - First Time Builder

Hi all, firstly, thank you...I have learned so much on these forums.

I am a hesitant first time builder of ESLs. I am several hours into a full-range segmented copper rod build for my first attempt, with (mostly) all parts ordered/delivered. I still can't seem to gain the confidence I'm seeking regarding transformers. I have ordered 20 Antek AN- 0206, 10 per channel.
My amp is a Crown 1002, 215W at 8 Ohm, 350W at 4 ohm, 550W at 2 Ohm.

If 25VA at 50hz = 12.5VA at 25Hz (low freq cutoff for full range esls?) Right? Don't I need to consider power handling (sharing the load amongst transformers)?

My d/s spacing will be about 1/8" + a very little for adhesive

Should I?:

1. Be satisfied with current components and go with 1:100 step up ratio: (120V* 10 (# of transformers in series) / 12V (low voltage windings in series)

2. Go with higher ratio (1:160, or 1:200) with 10 transformers per channel: (120V * 8)/ 6V = 160 ; or (120V * 10) / 6V = 200

3. buy 4 more transformers to make 1:120 step up ratio: 120V* 12 (# of transformers in series) / 12V (low voltage windings )

I really wish I understood what risks one takes with higher step-up ratios.

My goal (of course) is to not limit sound decibel levels, and maintain clarity of sound throughout possible frequency ranges (already aware some sacrifice is made below 40hz with full range esls).

Or maybe I'm overthinking all of this, and none of those details will matter so much?

Thank you very much.
 
Hi Tade, Orchidtheaf
Step up transformers for ESLs are a bit of a trick, and the problems become more difficult as you push to lower frequencies (more turns on the transformer), bigger panels, and higher step-up ratios.

There are four key specifications for ESL transformers
Step-up ratio: A typical 100 W amp produces peak voltages of the order of 40V, perhaps a bit higher. An ESL requires peak audio voltages (stator-to-stator) ranging from 1.6 kV to 8 kV, depending on the membrane-stator spacing (2.5 to 3mm is good for a full-range ESL). This means the transformer step up ratio should be in the range 40 to 200. 40 won’t cause any trouble, but achieving 200 without compromises on bandwidth will require everything to be right, and with some big ESLs it is impossible.

Primary voltage rating: This figure is frequency dependent. For example if you use a 120:12V 60 Hz power transformer backwards, then the voltage rating at 60 Hz is 12V rms only. With a 100W amp the transformer is likely to saturate (loose its input impedance) causing the amplifier current to rocket. If you limit the frequency to 120 Hz and above (twice 60Hz), then the voltage rating increases to 24 Vrms (twice 12 V). The voltage rating increases in direct proportion to the frequency.

Leakage inductance: Any coil of wire has an inductance, and so too do the primary and secondary windings of a transformer. Some of that inductance couples the two windings (mutual inductance) and some does not – the fraction that does not couple the two windings is called leakage inductance (its more complicated than this, but this explanation will do for the moment). The leakage inductance appears as an impedance in series with the ESL.

Winding capacitance:
Any two conductors placed close together have a capacitance between them, and there are little capacitances between turns on the transformer, between layers of turns, between the primary and secondary windings and between the windings and the core. The cumulative effect of all these capacitance is a single large capacitance that appears in parallel with the ESL. In combination with the leakage inductance this causes the transformer to have a second-order low pass frequency response – modified by the ESL.

There are two lesser things to add into the mix:

Primary winding resistance: To which must be added the resistance of the speaker leads. This resistance helps limit the current through the transformer if it saturates (stop the smoke getting out of the amp) and (ii) it helps damp the transformer resonance. Most people like the total resistance to be about 1 ohm.

The amplifier output inductance: typically 1 to 10 uH, to which must be added the inductance of the speaker leads (~0.7 uH/m). This adds to the leakage inductance of the transformer.

And then there is the type of ESL

Non-segmented ESLs behave as a single large capacitor, which adds to the transformer capacitance – may be up to 2 nF.

Segmented ESL: The load capacitance presented by a resistive segmented ESL is about 1/20 of the panel itself – makes it much easier.

Problem 1: Consider a large panel with capacitance = 1 nF, a step up transformer 1:100, and a 1 ohm primary winding resistance. This looks like an RC filter with the series resistance = 1 ohm x 100 x 100 = 10 kohms in series with the 1 nF panel. The cutoff frequency is 1/(2piRC)=16 kHz. A 1:200 transformer would cut off at 4 kHz. So you cannot run a large unsegmented ESL at high-step-up ratios with a useful series resistance.

Problem 2: Consider the same ESL with an amp with 3 uH OP inductance and 3 m of speaker leads – total primary inductance = 5 uH. The equivalent series inductance seen by the ESL 5 uH x 100 X 100 = 50 mH. This forms a LC filter with a second order filter with curoff frequency 1/(2pisqrt(LC)) =22 kHz. Once again, a higher 1:200 step up ratio would result in cutoff at 5.5 kHz. Even 1:100 leaves very little room to run a transformer. So large unsegmented ESLs require (i) amplifiers with a low output inductance, (ii) short low inductance speaker leads, (iii) transformers with a low step-up ratio and a very low leakage inductance (high wattage toroids are good). It is possible to run a moderate sized panel for a hybrid with high step-up ratios but not a full range ESL. Most commercial ESL transformers are made to drive unsegmented panels.

Problem 3: Ideally the 1 ohm resistor should damp the transformer resonance to give a Q near 1. This requires the total leakage inductance (amplifier+ speaker leads+ transformer), referred to the primary, to be about 8 uH. For high step up ratios, this favours transformers with a high leakage inductance and low capacitance – the opposite of what is available commercially.

So what to do?

First, if you want a large full-range ESL, consider segmentation (see other posts on DIY). Without it you will struggle to get a system with a good frequency response and without the tendency to kill amps.

Secondly, don’t buy commercial ESL transformers for a segmented ESL. Transformers suited to segmented ESLs can be constructed from small (15VA) power transformers run with the high voltage windings in series and the low voltage winding in series and parallel as required to get the voltage rating. For ESLs the voltage rating is more important than the power rating. Do not use transformers with the dual high voltage windings – they have a very high capacitance.

Thirdly, don’t be tempted to aim for high step up ratios unless you know how to model and calculate the frequency response of the entire system. Low ratios (100 ish, perhaps a bit higher) are far more forgiving.

Hope this is helpful – its longer than I expected by still not as helpful as I would like.
 
thank you for the thoughtful and detailed response, though I would be lying if I said I understood it all (or even half of it). I am a first time builder, with little to no electronics background. Everything I know of the subject has been learned in the last 6 months of research, reading Roger Sanders' book twice, and conversing with other builders. I am still a novice with a capital "N."

I guess I forgot to mention that I am building segmented ESLs, probably could have saved you some explanation. I will however study all that you have detailed, many times I'm sure, so that I may learn more about all of this. I cannot expect to know everything going into my first build...I really just hope to make something that sounds darn good, without frying expensive electrical parts. I had intentions to make a hybrid for my first build, but budget played a role in keeping things simple (no need to make a TL subwoofer, or secondary amplifiers, or digital crossovers). I am saving all of that for my next build IF, I can successfully accomplish my goals with this first build.

Regarding your comments about specifics of transformers; as aforementioned, I already bought 20 of the Antek AN- 0206 with the intention of making a 1:100 step up ratio. I also bought 4 power resisters to make 1ohm resistance which will be wired to the speaker leads (as you mention).

I used the ESL spreadsheet to determine resistor values for my segments.
My (adjustable) DC bias supply will offer ~4000V to the diaphram.

All in all, I do think you answered my question.

Again, thank you for taking the time.
 
…I already bought 20 of the Antek AN- 0206 with the intention of making a 1:100 step up ratio...
A lot of useful information packed into golfnut’s post.
Since you have already purchased your transformers, the question becomes how best to configure the windings for your application of a full range segmented ESL based on this information. For ESL step-up transformers it is mainly about voltage handling capability rather than power handling. With this in mind, to keep your transformer cores from saturating at bass frequencies you will need to put the 6V windings in series and also put more than one transformer in series. Attached is one option that will provide a step-up ratio of about 75:1 and should handle your Crown amplifier without serious core saturation issues or problems with corona on the bifilar 115V windings. Adding 4 more transformer using the same configuration would give you about 110:1 ratio.

Links to some related postings:
- Antek AN-0506 measurements and corona investigation
Antek Toroidal power transformer for Step-up, Measurements (part 1/2) #1
Antek Toroidal power transformer for Step-up, Measurements (part 1/2) #25

- VTX-146-015-106 measurements, response and distortion
About to take the ESL plunge #284
About to take the ESL plunge #292
About to take the ESL plunge #299

- Bass handling capability of small toroidal power transformers
DIY bass transformer for ESLs ? #6
 

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tyu

Member
2009-07-18 8:16 pm
....from justrealmusic...
Any input on his transformers ..... ..his prices seem vary fair for EI type...looks like more money for toroids...
"
Don't Be Fooled by others that say they have a full range Electrostatic step-up Transformer

One of the most important factor in a SINGLE ESL panel design is the esl step-up transformer which - at best - can only produce SEVEN usable octaves of flat frequency response. The transformer designer may choose which of the seven octaves he wants to build for.
Our Model 2.1 and 3.1 ESL have a usable frequency response of 175 Hz to 20 kHz with the M299B step-up transformer and crossover. Both models could be used down to 50hz with a higher turns step-up transformer say about 200:1 ratio but this step-up transformer would then only be able to produce up to 6khz in frequency response. I have personally bought both EI and Toroidal ESL transformers that cost up to $300 each, and have machine wound many a transformer. I have also measured and used over a hundred step-up transformers and NONE with a single output winding will produce seven or more octaves of flat response. Their only one way I know of (if you have another let me know) to build a full range ESL you must use two step-up transformers or one transformer with two secondary winding one for bass (about 200:1 ratio) and the other for midrange and treble panels (at least 50:1 ratio) for a full range ESL. Next the ESL and or speaker baffle have to be wide due to dipole cancellation (24 inches or wider or the sides folded back) to go below 100hz the laws of physics just can't be cheated.
There are many more factors that that goes into each ESL design but the two mentioned above are most important ones to start with.


Electrostatic Transformers-Esthetics
We have also paid close attention to our ESL transformer. Our units are manufactured with high grade M6 laminations and machine wound with high quality pure copper wire. The core is varnished and oven baked to ensure quiet operation-even at high ambient temperatures.

We have our ESL step-up transformers custom wound to our specs, we are constantly improving and tweaking their performance. The ESL transformer is one of the most critical components in an electrostatic loudspeaker. Our transformers are of EI the best M6 laminated design. We can offer custom Toroidal designs and are about three times the cost.
Most importantly, our designs are "ear tested". After a new design has passed extensive testing, it's got to sound good too, before we will put it on the market! From Bach to rock, our ESL step-up transformer maybe for you.

Our Interleaved Windings
The reason for our sparkling high frequency performance is the use of interleaved windings between the primary and secondary. All windings are machine wound with high quality pure copper wire. All models include multiple interleaved windings to maximize high frequency response.

Turns Ratio
Our ESL step-up transformers will improve the output efficiency of your ESL. The M299b transformer with a 100:1 ratio will have 6-dB more output then the M99 with a 50:1 ratio and 9 more dB for the M399 transformer. Based on a flat frequency response from 100 Hz to around 10 kHz and 1000 pf load (Model 2.1 12"x48" ESL panel) above that range they will have about the same output efficiency."


Transformers
thanks
 

tyu

Member
2009-07-18 8:16 pm
Well I guess any Audio speakers biger than a cell phone is out today.
I got out of the Audio bizz in 1995...the hand writing was on the wall then, for the small Audio shop. To bad about Justrealmusic...his price were to fair..i guess that's a death wish.....after time it gets not to be fun any more...
But wate its... "Make America Great Again"...right....I gess it has not trickled-down yet.
thanks of your info
 
I agree that the prices were really fair and I was really excited to grab a couple of transformers. I had a feeling before I called because of the last date the website was updated, I thought maybe the price was going to be increased since then but the news was worse. He was a really nice gentlemen and we had a good chat.

So I am back to square one, either running two Anteks or a Hammond 10k:4 push pull.
 

tyu

Member
2009-07-18 8:16 pm
well Bolserst.....is on top of the trans workings..an most things ESL, planer type setups....I trust him...he puts his hands on this stuff......an knows what well work best with what we have to use.....but you may know this...justsaying
I have tried the Hammond type...worket... but did not sound good..to me anyway
never used the Anteks...Toroidal....But ML use them in there speakers..sale for over $10k.....so thay must work well for 250-450hz an up....Jazzman gets good sound out of the Toroidal...this maybe your best bet....good luck
 
....from justrealmusic...
Any input on his transformers ..... ..his prices seem vary fair for EI type...looks like more money for toroids...
"
Don't Be Fooled by others that say they have a full range Electrostatic step-up Transformer

One of the most important factor in a SINGLE ESL panel design is the esl step-up transformer which - at best - can only produce SEVEN usable octaves of flat frequency response. The transformer designer may choose which of the seven octaves he wants to build for.
Our Model 2.1 and 3.1 ESL have a usable frequency response of 175 Hz to 20 kHz with the M299B step-up transformer and crossover. Both models could be used down to 50hz with a higher turns step-up transformer say about 200:1 ratio but this step-up transformer would then only be able to produce up to 6khz in frequency response. I have personally bought both EI and Toroidal ESL transformers that cost up to $300 each, and have machine wound many a transformer. I have also measured and used over a hundred step-up transformers and NONE with a single output winding will produce seven or more octaves of flat response. Their only one way I know of (if you have another let me know) to build a full range ESL you must use two step-up transformers or one transformer with two secondary winding one for bass (about 200:1 ratio) and the other for midrange and treble panels (at least 50:1 ratio) for a full range ESL. Next the ESL and or speaker baffle have to be wide due to dipole cancellation (24 inches or wider or the sides folded back) to go below 100hz the laws of physics just can't be cheated.
There are many more factors that that goes into each ESL design but the two mentioned above are most important ones to start with.


Electrostatic Transformers-Esthetics
We have also paid close attention to our ESL transformer. Our units are manufactured with high grade M6 laminations and machine wound with high quality pure copper wire. The core is varnished and oven baked to ensure quiet operation-even at high ambient temperatures.

We have our ESL step-up transformers custom wound to our specs, we are constantly improving and tweaking their performance. The ESL transformer is one of the most critical components in an electrostatic loudspeaker. Our transformers are of EI the best M6 laminated design. We can offer custom Toroidal designs and are about three times the cost.
Most importantly, our designs are "ear tested". After a new design has passed extensive testing, it's got to sound good too, before we will put it on the market! From Bach to rock, our ESL step-up transformer maybe for you.

Our Interleaved Windings
The reason for our sparkling high frequency performance is the use of interleaved windings between the primary and secondary. All windings are machine wound with high quality pure copper wire. All models include multiple interleaved windings to maximize high frequency response.

Turns Ratio
Our ESL step-up transformers will improve the output efficiency of your ESL. The M299b transformer with a 100:1 ratio will have 6-dB more output then the M99 with a 50:1 ratio and 9 more dB for the M399 transformer. Based on a flat frequency response from 100 Hz to around 10 kHz and 1000 pf load (Model 2.1 12"x48" ESL panel) above that range they will have about the same output efficiency."


Transformers
thanks

In my very first ESL built in 2008 (a hybrid with 12 x 48 perf metal stators) I used the Just Real Music M299 transformers. I'm a bit treble deaf so it could be my hearing-- but to me those M299's just sounded anemic on the treble end.

After reading one of Calvin's posts about cheap toroids, I replaced the M299's with a tandem of inexpensive Farnell 50VA 230V/2x6V power toroids and I was amazed at the improvement... the highs were pristine and I drove them with ridiculous power and couldn't hurt them. I've evolved through several ESL panels since then but I'm still using those very same Farnell toroids. Highly recommended for hybrid ESLs!!

I also did a quicky listening test (a few hours) with a tandem of 50VA Antek 2x115V/2x6V power transformers. These sounded just fine too (way better than the M299s) but I believe their dual 115V secondaries have higher capacitance and I don't trust them to be as robust (arc resistant) as the single 230V secondary toroids.
 
Last edited:
well Bolserst.....is on top of the trans workings..an most things ESL, planer type setups....I trust him...he puts his hands on this stuff......an knows what well work best with what we have to use.....but you may know this...justsaying
I have tried the Hammond type...worket... but did not sound good..to me anyway
never used the Anteks...Toroidal....But ML use them in there speakers..sale for over $10k.....so thay must work well for 250-450hz an up....Jazzman gets good sound out of the Toroidal...this maybe your best bet....good luck

ml uses 230-12 volt teroids ?
 
Okeeeej so one thing lets assume some one can theoretically design a rather ok trannie what would one pay for it ? pref C-cores so you can just wind bobines to spec and put it on the metal as you please. i wounded trannies before like 100's or so, but i knbow nothing about designing one. so if someone does we might be of help to each other and finally create some affordable ones ? i think i stated this sort of colab earlier in a thread. but it never came to something