new Trannies

[Calvin]

Hi Folks,

got me some new toroids 230V/2x6V, 50VA. Wired two of them in series (230V) and parallel (6V). This gives a factor of theoretical ~1:75 (in praxi it measures 1:68)

Here are first measurements of my panel (1.2nF) connected to these toroids in nearfield (10cm) (Spl is recalculated to 2m)

As one can see linearity is very good. The upper bandwidth is well above 20kHz (mic´s not compensated for and starts to roll off beyond 15kHz).

jauu
Calvin

[Calvin]

Hi Folks,

the impedance plot prooves the high bandwidth. Plots are nearly identical to those measured with the 1:75 Amplimo. The resonance of trannies stray inductance with the panels capacity is above 20kHz.

Conclusion: Even with high capacitive panels simple and cheap toroids work and they work better than lot of so called specialized audio-trannies!

jauu
Calvin

[dstockwell]

Is there a link to these toroids.

[Calvin]

Hi,

its a German company named BSAB. They distribute the Amplomos over here too :-))

jauu
Calvin

[goudey]

I measured the Avel Lindberg 50VA 115x2 : 6x2 transformer this morning (part number Y236200, two wired as above).

Effective turns ratio measures and calculates to about 68:1

The leakage inductance looks good, the effective secondary inductance looks not so good.

For leakage inductance (secondary, high impedance side) I get about 28 mH, which is good.

For effective secondary inductance, I get about 5.3 Henries. This is not so good, making to difficult to design a passive crossover, and being problematic for direct coupling to an amplifier due to low impedance at low frequencies.

Effective secondary capacitance is about 1200 pF.

The impedance curve shows a peak impedance at about 1400 Hz when loaded with 1000 pF. This is quite a bit higher (in frequency) than shown in the impedance curve above.

Apparently not all cheap toroids are built the same.

For comparison, the 75:1 Plitron ESL transformer specs are:
22 mH leakage
1600 Henries
800 pF

This transformer provides a very good higher impedance at low frequencies.

Another comparison, the E R Audio ESL transformer (my measurements):
22 mH
64.8 Henries
308 pF

[Bazukaz]

Distortion measurements would be very interesting ...
I doubt the core of cheap toroids is made of wrong steel and plates are badly isolated between each other.

Also , what do you think about taking one of secondary windings and making additional feedback to amp ? Wouldn't it decrease distorition caused by the transformer ?

[Capaciti]

Hi Folks,

first let me introduce myself. Since 15 Years I am an ESL enthusiast and gained some experience by building more than 50 iffernet types of ESL.

regarding toroids it needs to be said that standard transformers suffer from disadvantages as follws:

1. There is no insulation between the layers of the secondary winding. Additionally cheap transformers do not use double insulated copper wire. This means that there is a high potential of electrical short cut of the secondary winding depending on output voltage. The tested voltage handling capability is just true between primary and secondary winding.

2. The missing insulation of the secondary winding increases internal capacity of the secondary winding, which is contra regarding step-up ratio. In addition cheap transformers are wound very lousy,leading to crossing wires (results in additiional capacitance and short cut potential)

3. Typically core material of standard transformers is ferrite and not oriented and heat treated silica. Ferrite has its limitations regarding saturation and more important harmonic disssortion of the signal. Those ferrits are not designed for frequencies up to 20Khz.

In summary, toroids are really a good choice, but need to be specifically designed for ESL as well as EI or M-Types.

Do not expect miracles from cheap standard transformers.

Regards, Capaciti

[Calvin]

Hi,

I don´t claim the standard toroids to be superior to specialized toroids, but since the built is similar it was worth giving them a shot. And the results are very promising even with high capacitive panels in ML-style.

The backdraws Capaciti mentioned are true, but do they count in praxis?

1. Is special insulation on the secondary necessary? If the secondary is the low-voltage-side, than the answer is no. On the high-voltage-side it depends on the needed voltage-levels of the panel. Highly capacitive high-efficiency panels don´t need much voltage, and if the primary is wound in just one turn, the problem doesn´t appear anyway. We do need high dielectric strength between primary and secondary windings and this we have.

2. Is it of interest, when the reached transformation factor is sufficient? It seems that 1:75 could be limiting border for standard toroids. With even higher transformer ratios the demands will probabely too high.

3. Typical core material of nearly each power transformer I found on the net is grain orientated material with 0.3 to 0.35mm thickness. Anyway everybody can look up datasheets


In summary, within certain restrictions I see no reason not to use off-the-shelf standard toroids. The measurements I made with my panel showed an astonishingly close similarity to the excellent Amplimos but to app.1/10 the cost.

Still, I don´t expect wonders from these Trannies, but they are imo much closer to that than specialized and overprized ones

jauu
Calvin

[BillH]

Calvin, can we have some details of your ESL panel? I'm also wondering what crossover point you chose for the ESL.

I've just ordered four of these toroid transformers to try out. They should give about 50:1 step-up when connected in pairs.

[Capaciti]

Hi BillH,

really compelling pricing !

This transformer is small in size and has a limited core area. My guess is, that this transformer will show saturation if you go lower than 200-400 Hz (depending of input level).

It would be interesting to get some feedback from your trials with this size of toroids.

Whats the secondary output voltage required for appropriate sound pressure of your Panels ?

regards, capaciti