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Old 6th October 2013, 03:54 AM   #1
X83 is offline X83  United States
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Default Toroidal Transformers for ESL Panels

I'm searching for some toroidal type step up transformers with a 50:1 ratio to use with Martin Logan Monolith-III ESL panels and would like to find something that might be more economical than the Amplimo - Plitron step-up transformers. I noticed some of the people on this site are using the inexpensive standard power toroid's with 230V single primaries with 9V dual secondary's for a 50:1 ratio or the 6V dual secondary's for a 75:1 ratio and would be curious to know what model transformers work the best with the 24" X 48" size panels.

I'm thinking of using dual Multi-Comp VTX-146-050-109 toroidal transformers with a 50V 2.78A power rating or the VTX-146-080-109 with a higher 80V 4.44A power rating wired in 230V series and 9V parallel. http://www.farnell.com/datasheets/85993.pdf
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Last edited by X83; 6th October 2013 at 06:43 AM.
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Old 6th October 2013, 04:58 AM   #2
Calvin is offline Calvin  Germany
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Hi,

Is there a reason like a defect, that You want to replace the originals?
A couple of Years ago a customer asked me to do the same with his Sequel2.
The final result was, that it wasn't worth the effort.
ML's old speakers used vast amounts of equing, up to 15dB of electrical amplitude response. This amount of correction dwarfed any advantage a toroid might have offered. So, I recommended the customer to keep te original transformers and save the money ... which he did.
If You want the toroids to improve matters, it means a whole new design.
It is not the panels that are the pinhole of the old MLs, but the bass systems.
The panels alone would have been capable of seriously better performance with considerably increased efficiency, especially if the whole system would be activated.
But that would of course mean to design a complete new speaker.
So, if You want to keep Your Monolith as is, only tweaking the transformers with toroids will probabely be disappointing. The differences will be very small to nil.
Is there a special reason for a 1:50 ratio here? It is a fine value for panels of capacitance value close to 2nF. 1 nF and 1;75 give a good (impedance) match also. Values in between maybe interploated. 230/7V or 230/8V maybe better choices. Even with large panels I never chose 230/9V.

jauu
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Old 6th October 2013, 06:37 AM   #3
X83 is offline X83  United States
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I like the idea of using toroidal step-up transformers because they have a more efficient design than conventional E or C-core type transformers. The toroid transformers have less leakage flux and therefore they have significantly less leakage inductance. The stock E-core transformers are not as good in my opinion because the cores can get easily saturated and they have a high leakage & magnetic inductance which needs to be compensated for by adding 50W power resistors on the secondary side. Also the stock transformers only use outer part of the coil field on the secondary side because of these limitations. The Plitron's are good toroidal set-up transformers but the output is only rated around 70-watts and there are only three small 22-guage wires for the panels. I'm not certain of the wattage ratting used for the Monolith-III transformers but they have much thicker gauge wire size with a six wire output bridged at the PC board into three sections going to the panels. The ML CLS-II panels are the same size and use two of the same transformers wired in parallel with better results.

I have no problem with increasing the turn's ratio slightly but the panels impedance can dip down below 1-ohm in the 20kHz range which could cause problems with weak amplifier. My present amplifier is rated at 800wpc @ 4-ohms, 1600wpc @ 2-ohms and 2400wpc @ 1-ohm for a limited time basis. I removed the passive crossover boxes and I'm now using an active crossover which has much better results but there's still room for improvement with internal mods.


I also plan to mod the original bias power supply from 2.8kV to around 3.5kV which seems to help improve the sound on the older ML panels. The stock power supply has four 15M resistors for total of 60M-ohms to increase the voltage and lower the amperage to the panels. I plan to drop it down to around 20M and delete the two 1.8K-ohm power resistors which limits the bias power supply transformers voltage output.



If you know of any toroidal transformers that might work well in the 230/7V or 230/8V range please let me know the manufactures part numbers. I have also been considering the Antek brand which has dual 115V secondary windings. Antek - Transformers - Grid View
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Old 8th October 2013, 06:46 AM   #4
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I'm intrigued by the "Music Sense" input on the high voltage supply in the Monolith schematic. Is it used to turn the supply on/off and save energy or is there some other function?
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Old 8th October 2013, 08:36 AM   #5
Calvin is offline Calvin  Germany
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Hi,

it is used either for turning off the bias voltage fully or to reduce it to a lower standby value. Iirc the latter is the case here.
As we probabely all know, a ESL panel needs several minutes up to a couple of hours to sound optimally after switch-on. The longer so, the longer it has been off.
If it idles in standby on a reduced bias it comes up much faster, but the tendency to atract dust is lowered.

jauu
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Old 8th October 2013, 03:16 PM   #6
X83 is offline X83  United States
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Quote:
Originally Posted by phazer99 View Post
I'm intrigued by the "Music Sense" input on the high voltage supply in the Monolith schematic. Is it used to turn the supply on/off and save energy or is there some other function?
A pair of Martin Logan electrostats will draw about 5 watts maximum. There is circuitry to turn off the static charge when not in use; however, actual consumption will remain close to the same. The primary purpose of the sensing circuitry is to prevent dust collection on the electrostatic element.
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Old 8th October 2013, 03:27 PM   #7
X83 is offline X83  United States
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Is there any reason people are using dual primaries & secondary's other than they're easy to find? I was able to find some 230/8V toroids with single primaries & secondary's but they're special order.

What would make the perfect toroid step up transformer for ESL panels? Is there any problem with using the larger size toroids with the 200VA to 500VA rating with the same step up ratio? Also would it help to have a metal core with grain oriented structure and extra shielding with epoxy encapsulation? I'm thinking about having some custom manufactured or make them myself.

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Old 8th October 2013, 05:09 PM   #8
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Mostly single winding 230V transformer are hard to obtain on this side of the pond.

You may also have a better (lower) stray capacitance figure having one complete 230v winding rather than having two 115v windings wrapped one on top of the other.

A while back I had put one of Antek's AS-1206 through its paces and it seem to fair well to about 4500V of output.
But, this model has an electrostatic shield in it and in my opinion was the cause of its failure.

Try to stay away form these types if you can!
Hence the "AS" types.

Or unwrap the tape and low voltage winding and remove the shield and then put the LV winding back on.
Else DO NOT connect this shield to anything, not ground, not anything.

For two reasons,

#1 the insulation between the shield and the HV winding is thin and weak and may/will at some point cause a breakdown and arc through from the HV winding to the shield burning a few winding's thus shorting them out.


#2 the shield adds more unneeded stray capacitance to the transformer and therefore creates more load for the amplifier.

This Happened to me and I have it documented here,

Testing Your Transformer and Using the Transformer Test Jig

Here is the thread that shows the saturation tests,

A TEST JIG FOR FINDING ESL STEP-UP TRANSFORMER PARAMETERS

Typically you won't gain any significant performance by using a larger core if the HV winding is designed for 2X115v or 230v.

Except maybe only a very slightly lower THD on the low frequency side of things up to to the saturation point due to it having more iron, But I have not done any more tests lately to verify this.

I use 210 watt cores form a different company and they perform the same under identical conditions as the 100watt Antek AS-1206 that I have tested.

Everything is based upon this part of its parameter, and, unless it is designed for a higher voltage a 50,100 and 200 watt cores will have the similar saturation characteristics when it comes to feeding the LV winding.

Increasing the HV winding turn's is the only way to change this.

I had suggested a while back that maybe using one of Antek's HV trnasformere that has multiple HV windings might be a viable alternative and just add your own primary winding.

But it is a rather costly transformer to begin with.
Here is just one such example and may just work right out of the box,

http://www.antekinc.com/pdf/AN-4TK400.pdf

I have never tested one of these so I can't tell you what its stray capacitance and leakage inductance would be as this would determine what your high frequency performance would be.

By using the two 6.3V winding in series for 12.6v and the all of the HV winding in series would yield you a transformer with 1:81.7 step up ratio with good saturation performance down to 150hz or so with a 150 to 200 watt amplifier all in one nice package.
Or even down to the 50Hz to 100Hz range at lesser power levels with the 12v configuration.
By using it in the 6V mode could yield a 1:163.4 ratio with a low frequency point of 300hz.

This would be the nearly same cost of 4 of the smaller Antek AS-0506, But these are shielded types and they don't list the non shield AN-0506 anymore.

They do Have the AN-0206 core at $11 each and these may work just fine as well providing that you are using a crossover of above 360Hz or so depending on the power range of your amplifier.

Hardly any of these combinations will yield you anything good below 300hz anyhow unless you use 8 cores for just one panel.
Except maybe the above AN-4TK400 or something like it.

This is just a suggestion as it has not been tried before to my knowledge, But it may be a good possibility one wanted to give it a try.

They do have a few other cores that may work as well in a similar configuration but do stay away from the shielded "AS" types.

If you wanted to wind your own then you could start with a very large core from Alpha Core quite affordably.
But it is quite tedious to do.

Silicon Steel Toroidal Cores - In Stock

FWIW

jer

Last edited by geraldfryjr; 8th October 2013 at 05:15 PM.
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Old 8th October 2013, 09:02 PM   #9
X83 is offline X83  United States
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Thanks for the information and all the links above. Do you know if the toroidal O-cores are any more efficiency the standard toroidal cores? It seems if the windings have fewer right angles and shorter spans there would be significantly less inductance.

Has anyone tried using the AnTek AN-1212 - 230/12V or the AN-2215 - 230/15V toroids which are the unshielded AN version that could be interconnected to obtain a higher step up ratio? Theoretically the 12V should produce a ratio of around 75:1 and the 15V should be around 60:1 as in the schematic below.

Source page 128: http://home.kpn.nl/verwa255/esl/ESL_English_2011.pdf
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Old 8th October 2013, 10:57 PM   #10
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All of the 12xx series of transformer will have the same core size and same amount of turns on its HV winding, only the LV winding turns are changed.
Therefore the 12V LV winding will have twice as many turns a 6V Lv winding and all else stays the same!

A 12V/230v transformer gives about a 1:18.25 ratio and two cores wold give you only 1:36.5 not 1:75, it would take 4 core to get there with 12V LV windings.
In practice, With the transformer I tested I found it to actually be 1:38 for the 6V winding's and of course half that at 1:19 if they were wired for 12V.

For a larger core size your overall turns would be less as they are adjusted for the same 230V at 50hz operating magnetic flux level in the core material.

It would be great if we had the same amount of turns found on a much smaller core on a larger core, but that would be a waste of copper for the range of what they are designed for.

Every time you double the excitation voltage on any particular winding designed for a particular voltage without increasing its turns, you must also double its frequency in order to keep the core from going in to saturation.

Therefore if you increase the voltage at rate X then you must also increase the frequency by the same rate of X.

Using the Plitron 1:50 for example is actually a 17.5v/875v transformer designed for a lowest saturation frequency of 50hz.

jer

Last edited by geraldfryjr; 8th October 2013 at 11:16 PM.
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