Hehe, I was all ready to order four of these toroids and then I saw this power transformer. 120/240 volt primary and 9 volt at 2 amp secondary in a cute little package. Does cute count? 
From the spec sheet:
The twin primary and secondary windings are wound on separate bobbins giving maximum isolation for enhanced safety and low capacitive coupling. The near circular shape of the transformer core results in low magnetic flux leakage.
All transformers are subjected to 4.4kV ac insulation tests and manufactured to VDE 0550 Class 2, BS415 Class 2 and Insulation classification E 120 degrees C.
Does the 'low capacitive coupling' and 'low magnetic flux leakage' give any clue that these would suffer from the same drooping high end that Calvin has seen with audio transformers?
Edit: Grammar
From the spec sheet:
The twin primary and secondary windings are wound on separate bobbins giving maximum isolation for enhanced safety and low capacitive coupling. The near circular shape of the transformer core results in low magnetic flux leakage.
All transformers are subjected to 4.4kV ac insulation tests and manufactured to VDE 0550 Class 2, BS415 Class 2 and Insulation classification E 120 degrees C.
Does the 'low capacitive coupling' and 'low magnetic flux leakage' give any clue that these would suffer from the same drooping high end that Calvin has seen with audio transformers?
Edit: Grammar
great info! something more?
Hey Calvin: great to have the benefit of your transformer experience. Wonder if you could comment on possible step up transformers for the super tweeter project I discribed? Would it be possible to obtain response to up to 100K with ultra thin diaphragm (2 micron) and the right transformer (not custom made)? Figure 1/2 to 3/4 inch wide diaphragm and 6-8 inches tall (rough numbers) with the diaphragm split into two vertical sections and a vein (vertical) to keep one side from interacting with the other. Spacers at about 1/32 inch thick. Thanks for the assistance regards Moray James.
Hey Calvin: great to have the benefit of your transformer experience. Wonder if you could comment on possible step up transformers for the super tweeter project I discribed? Would it be possible to obtain response to up to 100K with ultra thin diaphragm (2 micron) and the right transformer (not custom made)? Figure 1/2 to 3/4 inch wide diaphragm and 6-8 inches tall (rough numbers) with the diaphragm split into two vertical sections and a vein (vertical) to keep one side from interacting with the other. Spacers at about 1/32 inch thick. Thanks for the assistance regards Moray James.
I have been following this thread for awhile, but I am a bit confused by a few things, and I hope someone can help me.
If there is a 8000 ohm to 4 ohm transformer what is the transformer ratio? Surely it's not 2000:1
What is a good source for the 220v to 9v toroid transformers I have heard of here?
And finally, if someone can answer this I'd be most grateful:
Can someone recommend a pair of transformers for a single ended amplifier that have atleast a 1:100 ratio, have decent phase and freq response, I don't need more than 15 watts of power handling (it's for headphones). Price for the pair must be less than 100 dollars, but preferably much less?
If there is a 8000 ohm to 4 ohm transformer what is the transformer ratio? Surely it's not 2000:1
What is a good source for the 220v to 9v toroid transformers I have heard of here?
And finally, if someone can answer this I'd be most grateful:
Can someone recommend a pair of transformers for a single ended amplifier that have atleast a 1:100 ratio, have decent phase and freq response, I don't need more than 15 watts of power handling (it's for headphones). Price for the pair must be less than 100 dollars, but preferably much less?
bjackson said:
I think there is some confusion here. The high voltage sides of the transformers should be wired in series. The low voltage sides should be wired in parallel for maximum step-up ratio. Alternatively, the low voltage sides can be wired in series, giving a lower step-up ratio, but maybe better load for your amplifier, depending on its stability.
Using two transformers with HV sides wired in series raises the output voltage and speaker sensitivity and splits the total power across the two cores (thereby raising power handling), and should give reduced distortion, among other benefits.
I_F
I was looking at Rod Elliot's ESL project. Page 3 has a wiring diagram for using four 100 volt PA transformers per channel for step up from the amplifier. He's getting 100:1 voltage ratio using the .5 watt taps.
A note from his website:
These transformers are universally available and have proved satisfactory for driving ESP1 panels, although potential users are warned that the transformers are being used beyond their rated voltage and there is a risk of breakdown. The risk has been reduced by using the series parallel arrangement shown in Fig.1 below. This limits the voltage across each transformer to about 600V RMS, which is still above the rated 100V, but samples used to date seem to be able to cope with this. However, there is room for a more satisfactory solution.
A note from his website:
These transformers are universally available and have proved satisfactory for driving ESP1 panels, although potential users are warned that the transformers are being used beyond their rated voltage and there is a risk of breakdown. The risk has been reduced by using the series parallel arrangement shown in Fig.1 below. This limits the voltage across each transformer to about 600V RMS, which is still above the rated 100V, but samples used to date seem to be able to cope with this. However, there is room for a more satisfactory solution.
Trannies connections
Hi,
different trannie connections and what its worth.
one of the biggest probs with trannies is to get their stray inductance down. Toroids are much better with regard to this point than other cores like EI or UI. The stray inductance and the speakers capacity form a resonating 2nd order low-pass. You can see this clearly in the frequency response curves and (!) the impedance curves. If the minimumm of the impedance curve lies within the audio band we have a prob (have a look at older MLs. They used terribly bad trannies that had the minimum around 10-15kHz). Using two bad trannies with an 1:2n connection doubles the inductance and hence the prob. On the other hand You might just need the higher voltage ratio.
There are five possible solutions.
1. live with it (restricted bandwidth) and built a complex crossover and loose efficiency
2. use better trannies like toroids (30-80VA) or trannies with higher power rating because these have lower leakage
3. parallel trannies (inductance is halved with every doubling of tranny-count)
4. use a specialized but very costly Audio-trannie
5. activate
using a couple of toroids might just work..using a quad of them will do, whilst giving increased power handling capabilities
jauu
Calvin
Hi,
different trannie connections and what its worth.
one of the biggest probs with trannies is to get their stray inductance down. Toroids are much better with regard to this point than other cores like EI or UI. The stray inductance and the speakers capacity form a resonating 2nd order low-pass. You can see this clearly in the frequency response curves and (!) the impedance curves. If the minimumm of the impedance curve lies within the audio band we have a prob (have a look at older MLs. They used terribly bad trannies that had the minimum around 10-15kHz). Using two bad trannies with an 1:2n connection doubles the inductance and hence the prob. On the other hand You might just need the higher voltage ratio.
There are five possible solutions.
1. live with it (restricted bandwidth) and built a complex crossover and loose efficiency
2. use better trannies like toroids (30-80VA) or trannies with higher power rating because these have lower leakage
3. parallel trannies (inductance is halved with every doubling of tranny-count)
4. use a specialized but very costly Audio-trannie
5. activate
using a couple of toroids might just work..using a quad of them will do, whilst giving increased power handling capabilities
jauu
Calvin
So would this do the job. And if so which tap to use. Rod mentions that you use the .5 watt tap on a 5 watt 100 volt transformer, these are 15 watt do to the freq response and the lowest setting is 1 watt. Now the other 70V transformer has a .62 tap, but freq respponse is not as good. Or should I keep this same setup and use two of the toroids.
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