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bobo1on1 27th February 2006 06:08 PM

Transformer for esl without center tap
 
2 Attachment(s)
I was wondering if you could use a transformer without a center tap for an esl by using something like 32 1 megaohm resistors in series connected to the primaries and connecting the HV supply between the 16th and 17th resistor and the membrane.


Also I was wondering how these small 1,5 VA transformers would work when using 10 of them, connecting all the primaries in parallel and all the secondaries in series, their frequency response could be very bad, but at 60 cents a piece it might be worth a shot.

SY 27th February 2006 06:30 PM

You could make a virtual center tap between the 5th and 6th transformer secondary.

I have an opinion on feasibility, but for 15 bucks and a couple hours, you can find out for sure, and that's much better than armchair speculation.

Bazukaz 27th February 2006 06:53 PM

Re: Transformer for esl without center tap
 
Quote:

Originally posted by bobo1on1

Also I was wondering how these small 1,5 VA transformers would work when using 10 of them, connecting all the primaries in parallel and all the secondaries in series, their frequency response could be very bad, but at 60 cents a piece it might be worth a shot.

Absolutely bad.Cheap trannies will have low inductance(will load your amp heavily), poor frequency response, and high levels of distortion.

Mains toroids for 12V lamps are a much better solution.

Do a search for thread "new trannies" , it was discussed here some time ago.

bobo1on1 27th February 2006 07:08 PM

Won't those toroids saturate heavily when driven above their rated voltage?
I can get 50 VA 2x 15 volt toroids for 8 euro a piece, these will be a better solution.

I wil have to make a good amp for driving them though, I dont want to risk blowing up my Onkyo.

Bazukaz 27th February 2006 07:18 PM

Small trannies saturate much quicker than large ones.The larger, the better... It is recommended to put a small value resistor ~0.5 ohm at amp's output. ESL to amp looks like a large cap , so resistor can prevent oscillation , which could destroy output transistors.
A simple amp for driving ESL can be built from LM3886 , as it is easy to build , and is very hard to destruct.

Regards,
Lukas.

bobo1on1 28th February 2006 11:44 PM

I might have a better option, 60 VA 100 volt line transformers from amplimo, I have sent them an email about what turn ratio they have but I have received no reply as of yet.

And another question, would it be ok to use a 5 meter 3 wire cable to carry both the audio signal coming from the transformer as well as the 3500 volt polarizing supply? The isolation is normal pvc.

hilbren 1st March 2006 07:01 AM

I would keep the cable as short as posible!
how thick is the pvc isolation your thinking about?

Calvin 1st March 2006 08:24 AM

toroids
 
Hi,

beeing power trannies, the toroids donīt saturate that easily. As standard trannies they are usable for mid-high-frequencies only -no fullrange mode- which reduces saturation probs further. a pair of 50VA types is sufficient to even drive big high capacitance panels. The voltage rating of the insulation is quite high and can be improved further by vacuum dipping with a varnish.

jauu
Calvin

Bazukaz 1st March 2006 12:09 PM

Quote:

Originally posted by bobo1on1
I might have a better option, 60 VA 100 volt line transformers from amplimo, I have sent them an email about what turn ratio they have but I have received no reply as of yet.

And another question, would it be ok to use a 5 meter 3 wire cable to carry both the audio signal coming from the transformer as well as the 3500 volt polarizing supply? The isolation is normal pvc.

Line transformers may have even lower turns ratio then mains toroids.I don't know about amplimos line trannies.You should ask for more parameters , like frequency response ,etc.
I have tried one 250W 220V/12V main toroid at 20 volts input(Reversed).The output was somewhere near 400V , and THD @ 1 khz was around 0.1% .Interestingly , THD rose with input voltage, probably due to increasing core saturation.
Frequency response went up to 20 kHz and more.Lower limit at this voltage was ~100-150Hz.
The transformer also produced quite much of sound itself :))

bobo1on1 1st March 2006 03:57 PM

Here is a quote from amplimo's website:

Quote:

These quality 100V-line transformers use a toroidal audio core and employ special winding techniques.
This construction results in several advantages:

1. A large frequency range of 20 - 35.000 Hz.
2. High efficiency
3. Sufficient headroom to ensure that core saturation is almost impossible. (Core saturation occurs when the core is too small or the primary winding inductance is too low. This causes severe overload of the amplfier).
4. Compatibility with any type of amplifier and loudspeaker. We have supplied these transformers for many years and no problems have been experienced with connection to any amplifier or loudspeaker.
5. Low internal resistances.
6. Negligible magnetic strayfield, allowing compact assemblies.
7. High reliability. Only first class materials and workmanship are used.
8. A good appearance compared to laminated transformers. Even after many years, no rust will be visible.
9. Convenient mounting using a single bolt.
10. Each type has an isolated 100V - 70V - 50V secondary winding.
11. All are supplied with a special RC-circuit. This protects the amplifier against current pulses, which can be caused by switching or can be picked up when using long 100V-leads.
12. These line transformers can also be used in reverse, from 100V to 4 or 8 ohm

The full 100V winding can be loaded with 100V-loudspeakers rated at the maximum output power rating of the amplifier.
The 70V tap can be loaded with 100V-loudspeakers rated at twice the maximum output power rating of the amplifier.
The 50V tap can be loaded with 100V-loudspeakers rated at four times the maximum output power rating of the amplifier.

The great advantages of a 100V system are:
- Low power losss when using long loudspeaker leads.
- All of the 100V loudspeakers can simply be connected in parallel.
They seem to be rather good quality, I still don't know their turns ratio though.
I am going to call the store that sells them.

Quote:

Originally posted by hilbren
I would keep the cable as short as posible!
how thick is the pvc isolation your thinking about?

I was thinking about the normal the normal power cord used for 230 volt applications, the isolation is 0,5 milimeter I think.
I have a better idea, if I use the wire to transport 24 volt ac I can feed that to the polarizing supply at the esl.


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