Please rec. step-up transformers for ESL

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I'm in the process of rebuilding a pair of Electrostatic Research ESL speakers and discovered that one of the step-up transformers is internally shorted. These are a 2 way design with a crossover point of 200hz. The transromers do not appear to have a usable part number. I really do not wish to use old opt's from some discarded tube amp. From the limited info Ive been able to get , the original trans have approx. a 75 to 1 step-up ratio. I'm looking for recomendations to aid my search for a pair of these . I am also willing to purchase a pair from someones past or unfinished project, provided they have been tested(used in system) and are of good quality. I only want to do this once. Help is greatly appreciated.
 
ok

Ok cheap, $10.00 70 volt line matching transformers can sound very good and only cost $20.00/pr. so start there run them backwards. They are leaky so expect a rising top end but that's ok with a heavier diaphragm. Probably a help.
People have posted impressive results with european 230 volt to 9volt step down torroid transformers, your second cheapest shot. Used Acoustat interfaces can also be had for very cheap find a pair of those. After all that you will have more experience than most and be ready to modify. Hope this has been of some assistance. Best regards Moray James.
 
Toroids

Hi,

Toroids work fine indeed. A pair of simple 230V/12V (for halogene lighting, giving 1:40) gave exactly the same results with regard to frequency- and phase- response as a 1:75 Amplimo.
Two 230/9V toroids give a step-up-ratio of 1:50, two 230/6V one of 1:75. Paralleling the trannie-pairs (e.g. as a quad- or hex-package) reduces strayinductance, hence rising the upper frequency limit if needed. Most of these trannies are tested for 4kV voltage, some even higher. I´ve lost quite some special made audio-trannies because of flash-overs and internal shortings but no standard toroid till now!
For most purposes 30W-80W-types will do fine.

jauu
Calvin
 
Re: Toroids

Calvin said:
Hi,

Toroids work fine indeed. A pair of simple 230V/12V (for halogene lighting, giving 1:40) gave exactly the same results with regard to frequency- and phase- response as a 1:75 Amplimo.
jauu
Calvin

Are you saying that a power supply transformer works well for the audio step-up?

Has you (anyone?) tried EI core power transformers?

I_F
 
IV

HI,

impedance measurements of my panel with an Amplimo, simple toroids and Somkbetzki-EI-types (1.Amplimo 2. toroids 3. EI-types).

The absolute value of the impedance maximums are indicators for the transformer´s stepup-ratio. The lower the imp-max the higher the stepup-ratio.
The impedance minimum at the upper frequency range is another indicator for the ´quality´ of the tranny (hence little stray inductance).
While both toroids´s minimum lies above 20kHz, the EI-types settle at about 14kHz (even though alrady 4 trannies are connected in series/parallel mode to get the stray-inductance down! It´s even worse using just a pair of EI´s!)).
The same can be seen in the phase response. With the toroids the phase response is more linear and closer to 90° than with the EI´s.
By paralleling the trannie-pairs the upper frequency range can be improved. But that only makes sense with standard toroids because of the high price of Amplimos or the still unsufficient result with EI´s.
Standard toroids often use the same core- and insulation material as good audio trannies, so there is no reason not to try them in first place. ;)

jauu
Calvin
 

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Calvin,

I may be repeating I_forgot here, but just trying to get this straight. Are you saying that you can substitute the audio transformer using for example two 230/12v toroidal power trannies in paralell to get a step-up of about 1:40?

If this is the case this seems like a much cheaper substitute especially for a first time builder. Is there anything else I should know about this?

furly
 
Calvin,

Do you think I could also use one of these in my DC power supply, or do you think the step up would be too large. Keep in mind i will have a 120VAC input. I guess i could always drop the voltage down a little if it is.

Or maybe i could use 3 in parallel for a ratio of about 1:60 for my audio signal to increase the voltage going into the stators . I'm thinking of these scenarios bc these transformers are cheap which is what i'm looking for right now!!

Any thoughts?

Thanks for all your help!

furly
 
Scroll down this page for five 70 volt transformers, and here's a page explaining 70 volt audio systems.

Allelectronics has a toroid transformer that looks like the right voltages, but low power handling. 115/220 volt primary, 8.5 volt at 1.1 amp secondary.

How does this look for wiring two transformers together?
 

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BillH said:
Allelectronics has a toroid transformer that looks like the right voltages, but low power handling. 115/220 volt primary, 8.5 volt at 1.1 amp secondary.

How does this look for wiring two transformers together?

That would be the way to do it. You could also wire the primaries in series for lower voltage out -unlikely you'd want that. However, if your amp should prove unstable with the primaries wired in parallel, you might try the series connection and see if the amp behaves itself.

A pair of those ought to have sufficient core area for driving an ESL.

I am still interested in hearing about how using power transformers works for driving speakers. Let us know your results...

I_F
 
Trannies

Hi Folks,

the question arose wether standard trannies are capable of good performance.

First a little History: when I build my first wire-stator-panels -which were a very low capacitance design- I bought trannies from a company that built ESLs their own. I connected 4 of them in series/parallel-connection for a ratio of 1:100. The results were not very pleasing with regard to measurements. Restricted bandwidth and phase-response. With my new metal-sheet-panels results were even worse. You can see it in the diagrams marked "..TR 1-100 EI-Type".
For me the trannies looked like 10VA-Types, so I bought me a bunch of cheap standard 230V/6V EI-Type power trannies and connected 6 of them in series/parallel connection. What should I say? The results were identical sonically as well as measured!! And while 3 out of 8 of the audio-trannies have been killed by internal flashovers the standard power trannies still work fine :mad:
Later I got the fantastic Amplimo Toroids with an ratio of 1:75. As the diagram prooves the measurements show excellent results. So I tried simple halogene-light-trannies (12V/230V) in series connection to give a ratio of 1:40. As can be seen in the diagrams, the results are very close to the Amplimo (differences in amplitude-response result from different measurement distances. Watch out for different scalings in the impedance plots!)
Apart from different SPLs and impedance levels the curves look pretty much the same with regard to upper frequency and phase responses and the apperance of the curves.
The upper bandwidth limit in frequency response results from a resonance of the panel´s capacity and the trannies stray-inductance. The point of minimum in the impedance curve around 10kHz to >20kHz defines the upper frequency limit (clearly obvious in the "EI-Type-diagrams). Too the phase response turns from theoretically 90° back towards 0°. Above that frequency the amplitude falls with 12dB/oct. So the impedance and phase curves are very good indicators for the trannies quality! With the Amplimo toroid as well as the simple halogene-lighting-toroids the phase is closer to 90° and more linear. The impedance minimum lies above 20kHz. The amplitude response is linear to 20kHz.
By using the standard toroids with a higher ratio the upper bandwidth limit will come down, but You may counter it by paralleling more trannies. Each doubling of trannie-count will result in a halfing of stray-inductance --> hence doubling the upper resonance-frequency/bandwidth limit.

Sonically I haven´t heard any differences between trannies with comparable frequency and phase-responses. Which isn´t such a surprise to me, because most trannies, wether they are marked for audio or other uses, feature the same core materials, the same wires and same insulation. The main difference are intersected windings. But with a toroid the coupling of primary and secondary windings is obviously very good and therefore stray-inductance is small. So there is hardly a need for more complicated and complex windings as in EI- or UI-Types. As long as the insulation is sufficient, standard toroids should work even better than most of the audio-trannies -- probably even with higher constancy of parameters and its much cheaper too ;) The insulation of power trannies standardly is specified to 4kV, sometimes even 5kV@50Hz or @400Hz (in Europe) which is more than sufficient for high efficiency-designs like the ML-Panels. Interestingly a ML-Prodigy panel measured originally 1:75 and with an Amplimo 1:75 gave much more linear results for the Amplimos. The positive sideeffect was, that the complex and efficiency-killing corrective networks could be omitted...leading to a drastically higher efficiency of around 96db/2.83V/2m and sonically to a more refined, clearer and more dynamic sound. :D With even bigger panels PA-uses come into mind, where a lightweight Panel with compact dimensions and the specific dipolar-cylindrical sound pattern could be very interesting ;)

I for my part strongly opt for trying standard power toroids in first case, before trying expensive ´audio´-trannies.

jauu
Calvin
 

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