Anyone know of a US source for ESL toroids?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Hi everyone,
I've been searching in vain for some reasonably priced toroidal transformers suitable for ESL's. I can't spring for those expensive Piltrons or Aplimos. I did find sources in Europe but all either didn't have an English language website or didn't respond to my emails, or wouldn't sell and ship to the US. Does anyone here know someone here in the US might get hold of some inexpensive 50VA 230V x 6V toroidal transformers?
much obliged, Charlie
 
Few,

Your knowledge of transformers can't be as limited as mine. I recall one of Calvin's threads reported favorable results using pairs of inexpensive 50VA 230v/6v toroids from some German company, which he wired up with the primarys in parallel and the secondaries in series:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=68573

I'm thinking these AN-Tek 50VA 230V/6V's might work out, even though they have dual primaries and secondaries [two 115v windings and two 6v windings). I think the trannys described in Calvin's thread used single 230V and single 6v windings.

If I've got it right, each AN-Tek tranny would need its two 115v windings series connected to form a single 230v winding and only one of the 6v windings would be used. A pair of these would then be wired together with their 6v primaries in parallel and 230v secondaries in series to power each speaker.

Coreyk,
How did you wire yours up?
 
Hi,

I think the trannys described in Calvin's thread used single 230V and single 6v windings.
That is right. While the primary-to-secondary insulation is usually designed to withstand several kVs the insulation between the secondary windings can be as low as 500V. And keep in mind that insulation values fall with rising frequency. Trannies are tested with low-freq signals. For audio bandwidth I suggest to calculate with just half of the datasheet value. So, as long as you don´t know how the individual transformer sections are wound and insulated the use of two equal "1prim-1sec-winding trannies" is the easiest way to get good and safe results. You can profit from the increased flashover treshold. While a single tranny might be safe to 3.5kV -i.e 1.2kVrms- in case the sec-sec-flashover treshold is at least of the same value as the prim-sec value. The double-stacked trannies would be good for 7kV -i.e. 2.4kVrms- under the same conditions.
Unfortunately there doesn´t seem to be a sec-sec-value given in the Antek datasheets, just a prim-sec-value. You might clear up that point before order.
Oh, some last hints.....these trannies are only good for Hybrids. The primary inductance defines the low-freq limit. With standard power toroids the inductance is too small for fullrange usage, but enough for hybrids from ~100Hz on. Higher wattage types feature larger inductance values (and lower losses). So the lower You intend to play the panel the bigger the tranny will be. Because of the low losses, those trannies will transform the capacity of the panel very immediate to the amp. High values of phaseshift will occur that stress the amp more than the lesser phaseshift of a worse and lossier tranny.

jauu
Calvin
 
Last edited:
Hi,

it doesn´t need to be a 300VA-core, because sizing up the core improves some parameters but deteriorates others. The Amplimo-toroids use 100VA-cores and this is sufficient even for driving large panels fullrange.
What counts in first place is the primary inductance value. The higher it is, the lower is the lower bandwidth limit.
It might help to read the papers and patent of Mr. vanderVeen et al.
Patent:
"step-up-Transformator", NL A 9300433 (in dutch)
Papers:
"Toroidal Step Up Transformers for Electrostatic Loudspeakers", Plitron Website.
"Theory and Practise of wide bandwidth toroidal output Transformers", 97th AES convention 1994, San Francisco
You can of course have Your special tranny wound to Your specs and probabely need to if You want a FR-tranny. Standard toroids are a very affordable way to get Your hands on a good quality audio tranny for hybrids.
How much bandwidth you can squeeze out of the tranny-ESL-system depends on individual factors. Just try ;)

jauu
Calvin
 
Power xformers for audio

Please correct me if I am wrong, but whether toroidal or E-core, aren't power transformers designed with high inductance, no regard for minimizing capacitance, high hysteresis core materials, and with an expectation of hundreds rather than thousands of volts?

I would expect the result to be a rather low upper cutoff frequency, not a lot of volts without risk of breakdown, high distortion at low amplitudes, and a major self-resonance in the audio band. Of course, I think it would be great if OTS power transformers would work, but never thought of trying it.
 
Hi,

core material of Audio trannies for ESLs and power trannies is often the same, especially so for toroids. Audio trannies using ´special´ core-material are easily detected by exceptionally high price tags. ;)
The upper bandwidth limit (major self resonance) is defined by the stray inductance and winding capacitance of the tranny and the panels capacitance. Larger panels and smaller stator-stator distances increase the panel´s capacitance and as such the resonance lowers in frequency. You can identify the resonance as the upper minimum in the impedance plot. On the other hand the impedance of the pure panel drops with increasing capacitance and You need smaller values of the transformation factor to match panel and amplifier. Luckily physics are such that smaller transformation factors allow for a raise of the resonance frequency as well as easier construction and an overall improved behaviour of the tranny.
With toroids stray inductance can be very low and as such the resonance frequency high (around 20kHz with a 2nF load possible!). Standard EI-cores are much worse here. But quite often the resonance is used to fudge the frequency response of the panel and to push up the highs a bit. Additionally it easens the stress on the driving amplifier. So You can use the worse transformer to correct for deficiencies in other fields.

Over the years I have tested many different trannies, specialized ones as well as standard types. Typically most of the specialized trannies failed sooner or later because of internal flashovers. The trannies that never failed were the standard toroids with single primary and single secondary winding connected as pair. Besides....most transformer manufacturers are very unwilling to supply even basic parameters of their trannies. So You don´t actually know how much voltage the tranny can withstand in reality.
Standard power trannys are almost always tested on prim-sec-flashover voltages (~4kV in many cases, and double with a pair). Audio trannies are not at all better in this regard.
So what does it cost You?
- You probabely couldn´t use the standard toroids for fullrangers (low prim-inductance). But for Hybrids they are fine.
- A pair would be of bigger size.
- the transformation factor is typically lower than 1:70 because 6V/230V is usually the highest standard value.

jauu
Calvin
 
Hi Calvin,

I was able to find a pair of toroids with only primary windings - 0-110-220. They were very cheap. Using 0-220 for testing, I wound 10 rounds of copper wire in and I got 2.6 V. That's about 1:85 ratio. I'm thinking of winding 3 sets of 10 rounds of copper wire and parallel them all together. What do you think?

Oh, the toroids are about 8 cm in diameter and rated for 200 watts. They're Chinese made and the rated capacity might be overrated. I think.

Wachara C.
 
Hi,

the count of turns defines the primary inductance. The primary inductance defines the lower bandwidth limit in first case. So for a sufficiently low bandwidth limit You need a lot of inductance, hence increased number of turns. Just 3x10 turns won´t lead You far. When You turn the windings try to wind over the ´complete´ toroid core once. Lets say You use 5 paralleled windings, each winding should cover an angle of 72°.
Do You intend to use one tranny in 1:85 mode or two trannies in 1:170 mode?
In the first case it is important to know how the 0-110-220V coil is wound!
Best would be if each winding-half covers half of the core. But probabely the windings are wound on top of each other, which might lead to insulation breakwown. The best insulation is always between prim and sec-winding.
Since You wind Your own sec winding You could even improve the insulation by winding some plastic band on the tranny before winding the sec-windings.
If You want to use a pair of trannies 1:170 would be a very high transformation factor which is only usable for low capacitance panels -->electrically segmented panels.

jauu
Calvin
 
Last edited:
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.