Please rec. step-up transformers for ESL

[homemade]

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.

[homemade]

WOW!!!Nobody?? I'll even take suggestions from some diyers that use 70v commercial systems. I just want to purchase something tried and true. HELP!!!!!!!

[moray james]

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.

[Calvin]

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

[homemade]

Thanks........I feel much better now!!!!!!!!!

[I_Forgot]

Originally posted by Calvin
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

[Calvin]

Hi Folks,

some measurements.

Comparison of a ML Prodigy-Panel and my own Panel driven by a 1:75 Amplimo tranny. (Both panels pure and via filter. The lower Fs and more pronounced high-frequency-response on my panel is due to a thinner diaphragm.)

jauu
Calvin

[Calvin]

Hi,

my panel with a simple pair of 230/12V halogene lighting trannies
(measured on different positions and distances). Obviously not much difference to the Amplimo (apart from effieciency). 20kHz is easily reached.

jauu
Calvin

[Calvin]

Hi,

the same procedure with a quad of Sombetzki´s standard Audio-Trannies (probabely EI-Type). Bandwidth is clearly restricted to below 20Khz. And of my initially 8 trannies only 5 are still working. 3 are already defected by internal flashovers

jauu
Calvin

[Calvin]

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